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varying conditionsr in n-eaous studies (e6. Isaacson? & Wickelgren,

1962; Kimbnle, 1963; Teiteltrum & H!ilner, 1953). Those studies which

have failed to replicate these finding-s have reportedly restricted lesions

involving only the dorsal portionl of th~e hippocenpuis (Eoitiano & Isaacson,

1966; K~vein, Setekcliev & K~anda, 190'4), or have employred a response of

low probability (Kinble, K~i~rby & Stein, 1966; Wiivocur &c Mills, 1969).

It is possible to construlct various cxplcnations of the un-derlyin,

nature of thle observed hippoca r3pectolyi:nducll, deficit; one such sugg~esticn

is thact hippocrcparl lesions in sole way: vitiate th~e aversive effect of"

the punishingp stirulus. Such a position would9 lead to the prediction-

that hip~potampectomisca Ss would be def~icient inl a wide range: of shrock

motiv-atel behav-iors. This does not appearn to be the case, however, for

hippocac~pcto-ized Ss are not necesterily r 1 'e;;le co;;~e to

control Ss ir. their ability to r-ster a variety of active avoidance

task~s.

In the typical onle-:fay active avoidance paradign Ss is required

to m~ove from one8 coSparttent of a ShuttletoX to a second in the presence

of a warnin,- signal to avoid an aversipe stimulus is delivered and 5 must

then perform the response in order to escape fro:: it. FollowringP completion

of the trial S is returned to the original com~partment of the shuttle-

box and the procedure repeated. Although Niiki (1962) reported that

destruction of the hippocampus had no effect on this variation of

avoidance conditioning, more recent invecstigations have indicated that

there is aI lesion-ind~uced deficit which, however, appears to be of a

lesser relative mag-nitude than that found in the passive avoidance

paradign (Ilc~iirew Thnonpson, 1966; 01~ton & Isaacson, 1967).







If the above avoidance paradigm is modified so that S is not
returned to the original compartment of the shuttlebox following each

trial but instead cust return to it as the response in the following
avoidance trial the taskI is retermedl two-:lay active avoidan~ce. Wh~en

compared to neocortically lesionled and sham operated _Ss, hippocampectom-
ized Ss appear to be facilitated in the acquisition of this response

(Isaacson, Douglas & H:ooe, 1961). It ha~s been svagested tha3t facili-
tation is due to the presence of a passive avoidance component involved

in the twro-way active avoidance paradign which interferes with acquisi-
tion in control Ss (S is required to return to the compartment which bas

most recentlyr been associated with aversive stimulation). Eippocarpec-
tonized Ss which have been de30onstrated to be relatively impervious to
the effect of the contingencies necessary for the instate-ent of the

passive avoidance response are not so hanpered and consequently acquire
the two-way active evoidance response more readily (Doug~las, 1967). The

slight deficit seen in the hippocampectomized Ss' acquisition of the one-
vay active avoid~ance taskr can also be related to the deficit hippo-
campectomized Ss manifest in passive avoidance. Here, however, the
hippocampectomized Ss' tendency not to avoid the compartment associated
with aversive stimulation retards acquisition relative to control Ss

(01ton & Isaacson, 1957).
A second formulation of the underlying nature of the hippocampal
contribution to behavior which, like the aversive stimulus position,
relates to the passive avoidance deficit suggests that hippocampal
lesions enhance the reinforcing properties of appetitive stimuli or,









alternatively, holds thiat the hippocaupal lesion in some fashion elevates

drive level relative to non-hippocan~pectonized Ss under equal levels of

deprivation. Jerrard (1Y98) bas briefly reviewed the literature which

supports this position and points out that in addition to the intina~te
connections of the hippoc~amps uith structures irnportant for physiological

homeostasis, behaioral evidence indicates that hippoca-pectonized Ss

are more active in both novel and non-novel situations, increase their

response rate for food and water, and? show slower extinction of a. food-

motivated running response. Although hippocampsctomized Ss have not

been formd to eat more food than control 5, they have been found to

drink; more w~ater. It has been argued th~t the increased drive

hypothesis h--s generally b~ee ab~adoned (DoucGlas, 1967). However, the

arguents r;arshalled against this position havre stressed the findlings
of the avoidance conditioning paradigms and reasoned that because

hippocam~pectonized. s do not appear to be rore sensitive to the drive.,
inducing properties of aversive stimuli than do intact Ss, it is

inappropriate to posit that the reinforcing or drive reducing properties

of appetitive stimuli night differentially affect hippocampectomized and

normal Ss. Such a critique is cogent only if the theorist holds that

a unitary or one-process theory of hippocampal function will explain the

whole spectrum of lesion-induced behavioral anomalies. Whether it is

possible to formulate a one-process theory of hippocampal function has

yet to be demonstrated.

The deficit seen in the passive avoidance performance of hippo-

campectonized Ss has also been vieued as a manifestation of a general

tendency towsards response perseveration or, alternatively, an inability

to inhibit responses. A considerable body of evidence is available in
ernwnnt nC crnah a nneltlan~ Ptroll (10~ICm1 lnrTl +%1+ rite emb~art rl







to bilateral hippocampal stimulation during the acquisition and ex-
tinction of a food-motivated straight alleyway running response showed
no difference in rate or acquisition when compar~ied to control Ss but

did require a greatelr numbr of trials in extinction. This finding has
been reliably replicated in rats following hippocanpal destruction

(Jarrard &c Isaacson, 1965, Rapholson, Isaacson &c Douglas, 1966). A
closer eratination of the phenomenon indica~tes that the interval

between extinction trials is an important variable to be considered,
for while the increased resistance to extinction is deoonstrable when

trials are spaced, the hippocampal lesion deficit disappears in the
massed presentation of the extinction trials (Jarrard & Isaa~cson, 1905;
Jarrard, Islacson &c Wickelgren, 1964). Both Peretz (1965) and Douglas
and Pribrea (1966) have reported that hippocam~pctomized Ss shnow shorter.
response latencies and a greater number of responses to extinction than
do control Ss. Increased resistance to extinction ha~s also been de:;on-

strated in the two-wiay active avoidance paradigm (Isaacson, Douglas &r
Moore, 1961).

However, Schmaltz and Isaacson (1967) have presented slightly
divergent findings concerning the performance of hippocampectomized Ss
in extinction. They ran hippocamplly lesioned and control Ss to complete
extinction in as many 30-minute free operant sessions as were required
for the attainment of their stringent criterion. No difference was found
between the experimental and control Ss in the total number of sessions

required for extinction. In addition, the hippocampectomized Ss showJed
shorter response latencies in only the first extinction session; no
differences between groups were found for any of the subsequent sessions.









Kaplan (1967) has reported that, hippoca-`meCtoiz~ed Ss show faster
extinction of a freezing reaction taken as initiative of a classically

conditioned esotional response.

The general inability of hippocampally lesioned Ss to inhibit

responses has been widely deconrstrated in a number of other situations.

Ellen and Wfilson (1963) found hippocanpactooized rats impaired in their

ability to inhibit one type of bar press and adopt a second following a

change in the response requirements for reinforce-ent. Both Niki

(1965) and Swianso~n and Isaacson! (1967) have demonstrated a hipopocampal

lesion-indluced deficiency in yielding to sticrulus control following

the initiation of SD-S6\ trainingP. How~ever, the latter authors also

demonstratel that hippoemparjctoized 55 could. rsedily acquire the

discrimination provided they were not subjected to a longZ past history

of continuous reinfrorcement for responding prior to the initiation of"

discriminastion training. Clark and Iseacson (1965) foundi that hippo-

campectonized 55 were less efficient than control Ss on DRL schedules

of reinforcement. A follow-up study by Scheltz and Isaacson (1966)

presented findings analogous to those of Clark and Isaacson (1965),

indicating that bippocampally lesioned Ss could perform well on DRL

schedules if not first subjected to prolonged crf training.

The apparently critical role of past learning in the demonstrar-

tion of hippocampal lesion-induced deficits in discrimination and DRL

performance suggested to some that the hippocampus wsas not involved in

the inhibition of behavior in general, but wras more specifically necessary

for the inhibition of well practiced responses. The demonstrations by

Kinble, K~irkby and Stein (1966) and Winocur and Mills (1969) that







hippoc-rmpectomized Ss showed. no deficit in their ability to inhibit an1
unlearn-d escape response from a small, elevated perch when the response

was punished lead to their fonrml statement of that position. H~oucver,
Isaacson, 01ton, Bauer and Swart (1966) and Teitelbaum and Mlilner (1963)

have presented contradictory data, indicating thait hippocanpectomized

Ss are deficient in withholding~ a natuorally occurring- response involving

a step-down from3 a platform to an electrified grid. The foraor authors,

who shooke the platform to increase the probability of response occurrence,

suggested that the escape response elrployed by K~imble, Kilrkby and Stein

(1966) was too weak or improbable in nature to adequaately reveal a

hippocampal lesion-ind!uced deficit.

Inhibitory deficits of hippoclr:Tctomized 55 have also been

widely examined within the context of exploration and spontaneous

alternation paradigns. Roberts, Dentler a';d Brodwick (1962) compared

exploration rates of hippocacpectonized and control Ss in T- and Y~-azes
and found no differences in initial rates, but a more rapid decrease in

exploration rate in control than in lesione-d Ss. An additional analysis
revealed that Ss with small hippocanpal lesions showed a moderately, but

significant, slower exploration rate decrease than controls, and that Ss
with massive hippocaupal destruction showed no rate decrease whatsoever.

Leaton (1965) studied opportunity for exploration as a reinforcer of a

T-maze turning response and found evidence for acquisition in normal and

shamn operated Ss while hippocaspectomized Ss were unable to overcome

perseverative tendencies and consequently showed no acquisition effect.

Forced training was instituted in the second phase of the experiment and

measures of" running speed were takecn. The hippocomp-eomized Ss showed

slower habituation to the reinforcer, indexed by a slower decline in









running speed over trials than control Ss. Kirkxby, Stein, Kinble and

Kimble (1967) examined perseveration of a T-:lae response as a function

of goal-box confinement. With short confinerment periods (50 seconds)

hippocam~pal lesioned S~s showed perseverative behavior while control

Ss spontaneously alternated their responses on successive trials. With

longer cojnfineeent periods (10 anld 50 minutes) both hippocam;~pctactomiz

and control Ss demon~strated spontaneouns alternation. A supplementary~

analysis revealed hippoccpectonionzed Ss( perseverate responses ~Der se

rather than responses to specified locations.

Studies of the effect of hippeDO palI- 1 lesions upon maze learning

have yielded rather` consistent results. In general, the hippocampa

lesion-ind~uced deficit is slightC, if present at all, in very simple

m~azes, but as caze complexity increases the lesion-induced deficit in

acquisition becomes increasinglyr more manifest. These findings have

been attributed to the hippocam~pectomized? Ss' inability to inhibit the

reentry of previously explored blinds and the greater frequency of

blinds in progressively more complex mases (Kaada, Rasnussen & KIita, 1961;

Kimble, 1963; K~imble &c Kinble, 1965). Hosteller and Thomas (1967) have

demonstrated that the hippocampal deficits in maze learning cannot be

attributed to enhanced thigeotax~is. The hippocampal lesion-induced

changes in spontaneous alternation and maze performance suggested to

Kimble and his co-wiorkrers (Kimble, Kirkby & Stein, 1966; K~irby, Stein, Kimble

& Kimble, 1967) that hippocampectostized 5s suffer from a reduced rate

of information acquisition. This position is incomplete, however, for it

fails to account for the uninspired acquisition rates hippocenipectomized

Ss demonstrate in alternative learning paradigns.








Although hippoceapectomized Ss appear deficient in their ability

to withhold responses in successive or go-no go discrimination problems

(Kimble, 1963), nmr~orus studies have demonstrated that they do not
differ from control Ss on a iiide variety ofT simultaneous discrimination

pr-oble-,s (Alleni, 19410, 1941; Brojn, Kaufnan &; MaIrco, 1969; Grastyan &:
Karaos, 1962; Hirano, 1966; Kimble, 1963; Kimble & Zackc, 1967; Swann,

193rr, 1935; Teitenaum~, 1964; webster &- Yoneida, 1964). Wlhen hippo-
caspectomized Ss are required to reverse such a discrimination, a.

pronounced deficit in shif~ting responding from that which was previously
reinforced to that which is nearly reinforced is regularly observed

(Brown, Kaufcan &c Marco, 1969; Kintle & Kintle, 1965; ?abet 1963; Stutz
& Rock~lin, 1968; Suanson & Isaacson, 1967; Teitelbau, 1961j; Thocmpson &:

Langer, 1963).
In an attempt to explain the changes observed in positively

reinforced behavior following hippcom~pectony in terns of the loss of a

single process contributing to such behavior in the intact orgainisl,

Douglas and Pribram (1966) developed a sophisticated neurophyrsiological
theory of "problem solving." Although~ the authors were initially con-

cerned with the hippocampus, they found it necessary to include in their

theory a second limbic system structure, the amygdala, in order to account

for the behavior of which hippocampactomized Ss are capable. Each of
these structures is postulated to be intimately involved in two distinct

processes underlying problem solvinga or discrimination learning: the

hippocampus-centered "error-evaluate" process and the complementary
anygdala-centered "reinforce-register" process. The terms are indicative
of the function of each: the reinforce-register process is depicted as









increasing the future probability of a response rh~ich has been followed

by reinforcement; the error-cvaluate process is postulated as decreasing

the future probuability of a response which has not been followed by

reinforce-.ent. During discsrnimiation learning in the intact organism

both these processes or systems are cooperative as behlavior is brought

under stimulus control.

The proposed neuronal system underlyir= the error-evaluate

process involves hippoc~omplly mediated inhibition in a Renshav-11-lke

mechanism within afferent systems which serves to "gate out" non-

reinforced stimuli. In the absence of the hippoca'pus non-reinforcement

cannot alter behavior and discri'iination learning cust be accomplished

by the remailin~g reinforce-register system. The effect of reinfcorce-

ment termed "inpellence" is incremental over reinforced training,

constant in size, and related to the magnitude of reinforcement and the

effort required for its production. At the primaryJ neuronal level,

impellence is depicted as involving normally occurring collateral

inhibitory processes in afferent syrstens. The work of" Dew~son, Nobel

and Pribrara (1966) and Spinelli and Pribram (1966) is taken as direct

evidence for the czistence of these proposed systems.

To sumarize the Douglas-Pribram theory: It has been suggested

that the hippocampus is a key structure in an error evaluatingr system

which mediates the effect of non-reinforced responses during learning.

Organisms with hippoc~apal disruption are rendered relatively in-

sensitive to the effects of non-reinforcement and are therefore required

to learn appetitively motivJated tasks via the remaining reinforcement







sensitive anyiglaloid system. Although thie theory is a posteriori
in construction, Dougla-s and Pribram (1966) do present some data
confirmi~n predictions made from the theory.

The present experiment focuses upon the hippocam;pus an~d its
proposed involverent in situations involving nonl-reinf~orced responding~.
An experimental pa~radig2 in wihich manipulation of reinforcement and

non-reinforcement contingencies generates differential predictions
concerning the behavior of hippocampectosized rats has been developed
from the theory in question. In both the acquisition and reversal

phases of a position discrimination, equation of" the absolute number
of reinforced responses to each of two to-be-discriminated manipulandla
combined with differentiation between the two in terns of the absolute

number of non-reinforced responses would be predicted from7 the theory
to retard both acquisition eand reversal in hippocarpectomized Ss when

compared to neocortically-lesioned andZ shank operated controls. However,
when the absolute number of non-reinforced responses to the Da~nipulanlda

are equated and the number of reinforced responses differ, any hippo-

camp~al lesion-induced deficit would be predicted to be of a significantly
lesser magnitude if present at all. Positive results would constitute

support of the Douglas-Pribram theory (Douglas, personal communication,
1968).












METHaOD


Lua e L
The Ss were 60 male LonG-Evans- rats approxi.-ntely 125 to 175

days old at the start of training.


bparatus

A total of four experimental chambers were employed. One was

constructed in the laboratory while the relainin= three were commercially

obtained. The chamber conlstructed in the laboratory was a converted ice

chest writh a sheetnstal partition dividing it into tw!o comprtments.

One colpzsrtnent contained a pellet dispenser and related reinforcement

delivery equiprment; the second compcartm~ent, with the inclusion of a

hardj'are cloth floor, mreasulred 28.5 r;. by 28 xa. by 23 an. high and

served as the experimental space. A Bazlph Gerbrands Company rat lever

was situated along the verticle center line of one wall, 2.25 cm. above

the hardvwarcloth floor. Reinforcemlent wias delivered to a food cup

situated 5 13m. above the manipulandun. An exhaust fan provided ventil-

ation, and a 20 VDC bulb located in the center of the ceiling provided

illumination during experimental sessions. The commercially obtained

chambers were all Lehigh. Valley Electronics M~odel 1316 small cubicles.

A metal food cup was located along the verticle center line of one

vall and rested on the grid floor. Two Lehigph Yalley Electronics Model

1352 rat levers were mounted on the same v'all, one on each side of the

food culp. The center point of each manipulcndum was 3 Em. above the







floor and 5 rm. from the nearest side wall. Illumination was provided by

a 20 VI)C bulb located 2 are, above the center of the plexiglass ceiling.

All manipulandla were calibrated so that a weight of approxicately 20

grams would activate the response circuitry. All expericental operations
and contingencies were controlled by automastic electro-sechaniical

progr~aming equipment. Reinf~orcerent consisted of 45 mg. Noyres rat

pellets. A plexiglass cover, measuring 3 na. by 7 me. by 14.5 mm. high,
was available to cover either ma~nipulandum in the two raznipurlanda

chambers, thereby forcing Ss to respond on the uncovered manipulandum

when the conditions of training so required.



The 60 Ss were assigned in equal unumbers to the 6 cells pre-

scribed by the first two factors of a 3 x 2 x 2 experimental design

involving repeated measures as the third factor. Animals subjected to

hippocom~pal, neocortical, or sham lesions (factor A) were assigned to
conditions of differentiation training which insured that for each daily

session either the number of reinforced responses or the number of non-

reinforced responses (factor 3) emitted on each of two mnpipulanda vere

equal, and were then tested in both the acquisition and reversal
(factor C) of a two manipulanda differentiation.

Procedure

Upon receipt from the supplier all Ss were placed on ad lib
food and water. Following recovery from the rigors of shipment a mean

base eight derived from five consecutive days weighing was established









for each S, an~d Ss were reduced to 850 of these values and maintained

at that level for the duration of pretraining-.

The goal of the pretraining phase of the experiment was to

establish in each S a bar press response free of any pr~ocedurally-

induced left or right position preference. To accomplish this pre-

training was coniducted in the single rani~pulandum chamiber. Subjects

were first magazine trained and then shaped to press the ma~nipulandum-

by the delivery of food reinforcement. Special care was taken to

insure that no 5 received a disproportionate amount of training under

crf and low FR reinforcement schnedules. The reinforcement ratio was

gradually escalated and pretraining was terminated upon each S_'s

demonstrations of' stable re3ponding under the requires-nts of an FRi 10

reinforcement sch-edle. Subjects were then returned to ad lib food

maintenance.

Following recovery of lost weight Ss assigned to thle appropriate

cells of the factorial design were subjected to bilateral hippocarjapal

removal, bilateral removal of the neocortex overlying the hippoczmpus,

or bilateral sham operations in which the dura overlying the neocortex

removed in the neocortical lesions was exposed. Following recovery front

surgery a mean base weight derived from five consecutive days weighing

was again established for each S, and Ss were reduced to 85; of these

values and maintained at that level for the duration of the experiment.

Subjects were then returned to the single manipulandun chamber

and retrained to respond under the conditions of the FR 10 reinforcement

schedule. With few exceptions reestablishment of control of responding

by the FR 10 schedule was accomplished during one session of appr~oximately







45 minutes' duration. In no instance did this retraining require more
than three daily sessions. FollowingS completion of' retraining in the

single manipulandumi chant~r Ss were advanced to the two manipulanda
chanters in which the experimental operations were conducted.

During prelimninary training in the two manipulanda chambers the

right manipulandum1 was first covered with the plexiglass cover provided
for forced training. Respondingp on the left rcanip3Rlul'rande first

maintained by a crf schedule of" reinforcement, and then by intermittent

reinf~orcement. The reinforcement ratio was escalated one step follov-

ing every~ tenth reinforcement until 10 reinforc~emets onan FR 10 schedule

were delivered. Subjects were then resoved from the chamber, the plexi-

glass cover maovedl to the left m~anipu~landu-3, and the preliminary training

regimen repeated. Those Ss which failed to earn 10 'R 10 reinforcements

on either manipu~ladu within a 5-ninute period duringP which that

schedule was in effect repeated the preliminary training regimen the

followiingb day. With few exceptions pretraining required no more than

one session approximating one hour in duration; in no case were more than

4 daily sessions required. On the day follorirng the completion of pre-

liminlary training the experimental procedures were initiated.

In discrimination acquisition responses on one manipulandum

vere reinforced onan FR 5 schedule and responses on the second were

reinforced on an PR 9 schedule. Of the 10 Ss in each of the two hippo-

campal and sham lesion groups, 6 vere assigned to one chamber and 4 to

a second. Within each group the relationship between manipulandum and

reinforcement schedule was counterbalanced. The two groups subjected

to neocortical destruction were assigned to the third chamber and the

relationship between manipulandum and reinforcement schedule also counter-










of a 5-ninute free choice pericd during w~hich both can~ipulanta w'ere

exposed for responding and reinforced on the appropriate schedules. At
the conclusion of the test period, which served! to monitor the f~orration

of the discrimination, the nuater of responc~es emitted and the hunter

of reinforceeaents earned on ea-ch r?nipuland8ir! were recorded. The

forced trainingn portion to the expeirilental session was then initiated.

The purpose of forced training differed for each of the two

hippocamp~al, neocortical, an~d shce lesion gr~oups. One each of the

hippocr-!pal, neocortical, and sham lesion groups wans run under the

condition prescribinge the eluztion, for each S, of the absolute nucfoer

of reinforced ressonses e-itted onl each~ Panipulanian during each

daily session. The second hippocamplly, neocortically, and sha;

lesioned groups we-re run under thle conditioning pirescribicg the'

equation, for each S, of the absolute nusber of non-reinforced

responses emitted. onl each manipulandun during each daily session. It

should be noted that as a result of the utilization of an FR 5 and an

FR 9 schedule of reinf~orcement, As which emiitted an equal number of

reinforced responses on each manipulald~ul also emitted twice as many

non-reinforced responses on the FR 9 manzipulanduml as on the FR 5

manipulandum. Conversely, Ss which emitted an equal number of non-reinforced

responses on the two manipoulanda also emitted twice as many reinforced

responses on the FR9 5 manipulandun as on the FB 9 manipulandr.um

Subjects assigned to the reinforced responses equated procedure
fulfilled a dual requirement during each complete experimental session.

These reqluircments were: (La) each S earn an equal number of reinforcements








on the fa 5 and ra 9 nminulanda,, and. (b) a total of at lest 50 rein--

force-ents be earned on each of the tw!o manipulanda. If 5 did not

earn the minious 50 reinforcenants on either manipulandll during the

5-minute free choice period, the forced training portion of the

session inv-olved r-esponding! on both hanipulauda.. At the en~d of the

free choice period the required number of mak:e-up reinforcements to be

eared. on each mainipulandoni was determined, one manipiulenda~ was

covered, and S waes allo-ed to respond on the second until the required

number of nake-up reinforcers3ts for that nmanipu~landum3 had been

delivered. The cover vas then moved to the second 3ianipulendu and

S. was allowed to respond on the first until the requirements for tha~t

manipulanduaJ had been fulfilled. For a i~ple, if _S earned 40 FR 5

reinforcelents and 25 FR 9 reinforcements dur~inga the free choice

period, S would be required to earn an additional 10 FR 5 reinforce-

ments and 25 FR 9 reinforcements during the forced training period.

As a result, 5 would have earned. an equal number of reinforcements (50)

on each manipulanxdum during the course of the experimental session.

The order in which the emaipulanda were covered alternated. across

daily sessions.

If S earned 50 or more reinforcements on either, or both

manipula~nda during the free choice period, the forced training period

involved responding only one manip~ulsadum. At the termination of

the free choice period. the difference between the number of reinforce-

ments earned on the two marnipulanda vas determined, and the manipulandum

on which 5 had earned the greater number of reinforcements was covered.

The S was then alloured to respond on the second manipuland~um until the










required no::M~r ol me'e-up reire~olce-clts as delivered. For cn~nple,
if S earned 65 F3 5 reinforce :inus all 20 FR 9 reinforcezonlts duri-n,

the free choice period, thie FR 5 oniipulendum vould be cosered. during

the forced traiirrel period arnd S would be allc::ed to respond on thre FR

9 manipulnaedrua rtil lj5 reinfrce:;-nts h-.d teen delivered. This ful-

filled the requirelent thast S eait an equenl materp of reinforced

responses, in this instance 65, on each cenipulentum, during: each experi-
muental session.

Subjects easign~ed to the non-reinforced responses equated

procedure fulfilled a different dual requirercnt iuringo each exiperi-

m~ental session. These ree~aire--onts were: (a) ench _5earn trwice as

mn~y reinforcer"i ts on tle TR 5 T2nipulcanU as on the Fr' 9 caniipulaseri,

and (b) a cini~l.= o C0 reiforcerents t ea-rnal on the FR 5 r-nipulman~z

and, consequently, a minimum of 30 reinfor-cerents be earned on the

FR 9 manipulantul. The free choice perio'l and subsequent forced train-

ing proceeded in a rannier aalogous to that described above for the Ss

assigned to the reinforced responses equated regicen. In the present

condition, if S failed to earn the m~inimu3 60 and 30 reinforcements on

both the FR 5 and PR 9 ma~nipulanda, respectively, during the free choice

period, the forced training peric-3 would insure that these minica w~ere

earned. For ex~a-ple, if S earned 1;0 FR 5 reinforcerments arnd 25 FR 9

reinforcements during the free choice period, he would be required to

earn an additional 20 FR 5 reinforcements and 5 FR 9 reinforcements

during the forced training period. The S would have therefore earned

the mlinimu 60 and 30 reinfor~celents on the FR 5 and FR 9 mainip~ulandae

during the course of the experinental session.







If S earned m~ore than: 60 reinforcenants on thle FR 5 oanipulandua7

and/or more than 30 reinforcements on the FR 9 manipulandumj during the
free choice period, the forced! training period involved only one manipu-
landul and served to insure thzt the ratio of reinforcements earned of

the FR 5 nanipulanduai to those earned on the FR, c anipultendum was 2 to 1.
For exaoptle, if S earned 70 PR 5 reainforcemenlts anl Iro PiR 9 reinforce-

ments durign thez free choice period, S was reqiuired to earn an additional

10 FR 5 r~einforcelents du~rin,- the forced training period. As a result,
S earned a total of 80 FR 5 reinforcements and 40 FR 9 reinforcements

during the course of the experimental session, and fulfilled the require-
mient thast the ratio of FR 5 to PR 9 r~einforcerments be 2 to 1. If S learned

90 FR 5 r~einforcements a~nd 10 FR 9 reinforecaents during the free choice
period, S vas required to earn an adlditionsl 35 FR 9 reinforpcelents
during the forced training period. The S therefore learned a total of 90

FRi 5 reinforcements and 45 Fa 9 reinfrorcEements, and the ratio of FR! 5 to
FR 9 reinforcements t'as again the required 2 to 1.
Discrimination training was terminated when S attained a
criterion of at least 90," responding on the FR 5 annipulandua in 9 of 10
consecutive free choice periods. Upon completion of this requirement
S was subjected to one half again as many daily sessions as were req~uired.
for attainment of the criterion and then moved. to the discr-imination

reversal phase of the experiment. If it becsae statistically impossible

for S to satisfy the criterion within 40 days of training~ 5 was con-
sidered to have failed to satisfy the requirements for discrimination
and was then moved to the discrimination reversal phase of the study.










Discrimin~atio~n revercal training wa~s ins~tituted for ea-ch S

on the day following_ termination of thle acquisition portion of the

expericernt. In reversal training, the rehztionshlip bet ea rein~force-

ment schedule and9 ranipuiledul wras reversed for each: S. Trainin~g

in rever~sl pr~oceeded in the srame fashion for the two groups as

described in the acquisitions phse above. Rever~sal training~ vas

termiinated when-o each S cet either the crilterion of acquisition or

failure e~stablishled for the acquisition pha~se of th," stu-ly.


Suroery

All Ss r-ere operated under L'0 c-fg H^Etutal anesthesiai

supple:,ented uith .30 cc. of atropine injected inlt rcLitonealll y. All

operations wiere Per1~Formed while S was held in a Ealtisor~e ste--eotaxic:

insturunent. A diissecting scope va-s E-plcfed t0 assist in the visual

guidingc of" reocortical and hippocarpal removal. In all operations thne

skull wass exp~osed by sans of a midline incision, bilateral trephine

holes were placed lateral to the midline and posterior to bregma. The

boles were enlarg-ed w-ith rougures to expose the neocorter overlyingP

the dorsal and lateral portions of the hippocampus. In the shan operated

Ss surgery was termlinated at this point. For those Ss sustaining neo-

cortical removal the dual was cut and the neocortex overlying the hippo-

campus wias aspirated of f, with care taken not to damage the hippocampus.

For those Ss subjected to hippocam~pectony the operation proceeded until

the thalanus was exp~osed. In addition, hippocazmal removal was expended

anteriorally as far as the hippocompal commais-vure as well as extended

around the posterio-lateral surface of the thalat1us. Care was taken not




23


to ED-age the thalarus. Following completion of surgery Ss Fere

returned to their home cages and maintained on a water and tetracycline

solution for three to five days.




Folloiviy the tern~~sictics of the experiments all 5s were sacri-

ficed. with a lethal dose of Nembu~tnl anesthesia a-nd intracardially

perfusedl with Eliline followed by a 10,$ fornelin solution. All brains

were then rezovedi from the br-ain cavities an~d those of thle Ss in the

neocortical andr hippocanlpal groups were infiltrated with, and embedded

in, celloidin ad section~ed at 15 u. Every tenth section was retained,

nounted on a slide, arnd stiaind with thrionin. In addition, for 5 ss

in eachi lesion group the section follorwing the thionin section was

stained with wile and then sounted.











RISUrLTS


Tracing~ of" representative cross sections through the hippo-

canpal and neocortical lesions are presented in Figares 1 anti 2,

resPectively. Hippocamcpal destraction regularly involved at least 75;;
of that structure anid in all instanlces resulted in the complete

separration of it- dors;al ad lateral aspects of the2 hippocampal forc-

ation. Specific damage to the thelRa~s was ninical and, when evident,

was typically unillatera~l in nature. The neocortical lesions did not

encompass a voles of tissue cocpr;abele to that renoiel in the hippo.-

canpal lesions;, bat did aprox-sir:te the rLeocortical des-trction incur-red

by the hippoca-pactooles. H;ippc1ampal decage resulting frol the neo-
cortical lesicns was minical and, if present, usually unilater'al in

nature. GrPoss exam~ination of the intact tnrains of those Ss subjected

to shea operations~ evneale no discernible neocortical damag~e.

The sepssions required to attain criterion in acquisition and

reversal by those sham, neoczortically, ardl hippcampally lesioned Ss

trained under the rein~forced responses eq~uated regimen are presented in

Table 1. The trials to criterion for Ss assigned to the non-reinforced

responses equated condition are presented in Table 2. Irspection of these
tables suggests there is anJ inverse relationship between performance in

acquisition and reversal. It appears that Ss who readily attain criterion

in acquisition are retarded in reversal and, to a lesser degree, Ss

who are retarded in acquisition appear to perform well in reversal. To

test the possibility of suchi an in-rerse relationship, all Ss were ranked



































Fig. 1.--Tracin s of representative cross sections through the
hipprcampal lesion (Af er Pellegrino and Cusban, 1907).


/'. L ..

~'-~--~-J;ii

















;i ii
p C;:
i-i



i "-,
i




u
d


FiE. 2.P-Trcings of representative cross sections through the
neocortical lesion (After Pelle,"rino and C71 n71, 1907).








TABLE 1

TRIALS TO CRITHION: IN ACQISITION AN!D PUTj~aIEMA EDR SRA~:1, NEOCORTICALLY ,
AN~D HIPPOClaPA~LLY lSIOEIID Ss ADSSIGED:~ TO THaE RESINFORCE
RESPOi:SES EQU~iATD CO:!DITIiOli



Acqluisition Re~versal


Sha Control


Neocortical Lesion


Hippoempal Lesion






28

TABLEL 2

TRIALS TO CR~ITJRIO: Ill ACnJISITIONr K D R":1~T h0 FO :"2-, fi'CORTICATLY,
AND HIPPOCELLL~IY I SIOIID Ss ASSIi:7 40 TO TE S01!-
&2~1870200) RLI:S : 1 :.to CO :DITIO;:


Acquisition Rve~cr:1

Sham~ Control 21 12
10 32
15 13
13 16
9 24
10 40
9 22
10 32
18 16
11 22_

Neocortic 1 Lesicn 10 17
11 19
40 15
13 13
12 12
10 15
10 20
10 16
31 14
9 13

Hippoc 1gn Lesior 11 14
11 25
19 14
16 14
10 12
9 17
9 40
10 17
10 14
10 12








from low to high on the matber of sessions to attain criterion in

acquisition, and from high to lold on, the number of sessions required

to attain criterion in reversal. A Spearcan rank: order correlation

coefficient (rs) was then computed (Siegel, 1956), and found to be

significant (rE; = .47, t = 4.0567, at' = 59t p <.001). sp~eaman rnkl
order correlation coefficients were also co7putEd in the same nsaner

for the shcz, neocortical, anid hippocanpal lesion groups (see Table 3),

and for the three lesion groups when further divided on thle basis of the

reinforced versus non-reinforced responses equated dinension (see

Table 4). The form-er analysis indicates the inverse relationship between

performance in acquisition a~n? re-ve-sal is present in only the shce

control Ss,; the latter analysis reveals that c-hil~e the shat control 5_s

under the non-reinfiorced responses equated condition do show this

relationship, their counterparts under the reinforced responses equated

condition do not. In addition, the finer grain analysis indicates that

the hippoctapectolized 55 murder the reinforced responses equated con-

dition also mnrifest this relationship, albeit to a lesser degree.

The sessions required to attain criterion in acquisition and

reversal for sham, neocortically, and hippocaapclly lesioned S~s under

the reinforced responses equatedl requirement are presented graphically

in Figu~res 3 and 4, respectively. Analogous data for Ss under the

non-reinforced responses equated condition are presented in Figulres 5 and

6. An analysis of variance assessing the effects of the three lesion

conditions, the two response-reinforcement contingencies, and acquisition

and reversal upon performance as indexed by the trials to criterion

measure was performed (Winer, 1962). Since the trials to criterion






30

TABLE 3
SPEA&l! PJOX BORDER CORR"~LATION COTUFICI :3? (r ) FO3R SH1,
NEO3CORTICAL, ANDn HIP;OCA3?A~i L 1C G'J.0PS"



Sham Contr-ol rs = .51
p <.05

Neocortical Lesion rs = .10


Elppcmcpal loseion rs =.3
p >.05


QSee text fOT r&:1:n aP25Eio'





31

TABLE 4

SPEARRAN RLUKf ORDER CORRSITION6 COFFICIN;TS (r ) FOR SKS', N-OCORTICAL~,
ANID EIPPO)C?:PAL ~IDSIO GROUPS UNDER EQULTED REINFJORCED
OR ~OI:-REINFORD.CED ICSPONDING DURI ;G TXINP(ITC~



REinf~orced Response ~ on-Reinfo~r-ced Responses
Equted. Equated

Sham Control rs = .42 rs =.7
p> .05 p <.01

Neocortical Lesion rs =.01 rs = .29
p>.05 p>.o5

H~ippoc 1r~ Lesion rs = .68 rs = *35
p<.05 p>.05

ESee text for rank-in~g procedure.



















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rceasure prod~uced slightly s're::cd data, these va~lues were subjected to a

square-root transformation a~nd a second analysis of variance performed

upon the resultant data. The results of these tco analyses are presented

in sn .?; fashion, in Tables 5 and 6, respeictively. A co-lparison of the

two tables reveals little incoinsistency in the results of the~ two

analyses.

An exam~ination of Figure~.P 7, which depicts thle cumulativii e per-

centage of Ss in each lesion group attaining criterion in successive

five session blocks, suggests that the neocorticslly and hippocnpally

lesioned- Ss are slightly facilitatel with respect to thie s 2 control

Ss in discrioiination performanc". Th~e aalyses of varia-ce indicate

thcat this difference is not lazrge encugh to be statistically reliable.

However, the results of the analys"s do reve7l a siDalfica~nt interaction

between this factor andl the acquisition and reversal phases of training

which rsust be exam~ined before it can be con!cluded that ths various lesion

conditions have no effect on discrimination learning.

A comprison of the effects of equating either reinforced or non-

reinforced responses during discricination training- is depicted in

Figure 8. Neither level of this factor, nor this factor's interaction

with the lesion dimensions, were indicated by the analyses of variance as

differentially- affectingp perfomance in the discrimination taskt.

Inspection of F'igure 9, which represents performance in the

acquisition and reversal phases of the study, suggests that Ss attained

criterion more rapidly in acquisition training than in reversal training,

and this is verified as a significant difference by thn analyses of

variance.








TABLE 5

ANALYSIS OF VARIA"~CE Oil TRIALS TO CRITERLION



Source M;S df" F

Between ss 59

Lesions (A) 117.11 2 2.23

Response--R~einf orcenent Contingency (B) 151.89 1 2.90

Ax B 2.79 2 0.05

S~s lithiu Groups (Error) 52.46 54

Vithin Ss 60

Acq~uisition-Rever~ssl (C) 795.69 1 7.93'
Ax C 4117.62 2 4.16'*

B x C 1.86 1 0.02

AxB xC 83.21 2 0.83

C x _Ss W;ithin Groups (Error) 100.35 5',


'p < .05

**~p <01










TASLE: 6

ANALYSIS OFP VABRIANCT: 0 SQUARF3~-ROOT TR? ISiOE!XTIONj 02 TRIALS TO CRITERION



Source MiS df F


Betwieel ss 59

Lesions (A) 1.23 2 1.7

Respon~se-Reinforc t Cottin ncy ( ) 1.38 1 1.91


0.02 2

0.22 54


Ss Witn Gr~oups (Irror)


60

10.96 1 6.61"

5.42 2 3.2P
2.01 1 1.21

0.04: 2 0.02

1.66 5';


Pithin Ss

Acquisitio-ir-rsevel (C)
Ax C

3 x 0

Ax B xC

CI xs Wvithin G~roups (Error)


Qp <05











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As vindicated previously, a sign~if~c-nt interaction bet::oon thei
lesions factor and the acquisition sand reversal phrases of training was
revealed by the analyses of" varioace. The co-?ponents of the inter-

action are depictedi in Figu~re 10, whnichl presents the per~fornarace of

the three losion groups in acq~uisitiion training,, and in Figure 11,
which presents their perfor::mnrce in reversal trainin,-. The mean trials
to criterion for Ss in eachl of the throc lesion groups is presented
for acquisitions? and reverce.1 in Figure '12. Examination of these

ficares sucgests t'-t the three lesion groupFs did not differ in the

acquisition ph-se of training, hlt that in the reversal ph~se the3
neocortically and hippocragally lesioned Ss, while not differin3 a ong3
the-:selves, did attain the criterion? core r;pidly Reld in greater Lu:terss
than the shanl control Ss. A tosterioril comparisons bat::een the cell

mceanis involved in this interactions wer~e performed utilizing the
Studentized rangeo stiatisic (:inecr, 1962). The results. of the compari^

sons are presented, in surstary fashion, in Table 7. The results support
the above observations a!d. reveal, in addition, that shan control Ss

attained criterion significantly faster in acquisition than in reversal,
but that such a difference is not present in the neocortically and

hippocampally lesioned Ss. Neither the r~e-aining first order inter-
action (lesions by response-reinforcement contingency) nor the single
second order interaction (lesions by response-reinforcenent contingency

by acquisit ion-reverjsl) attained significance.










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TABLE 7

STUDENIZEI RAN1GP STATISTIC A PO"7TI TESTS





Shan vs. Necocrtical Lesion. 3.01

Sham vs. Hippoccanpl Lesionl 0.86

seocortical vs. H~ippocompa;l Lesion 0.83




Shan3 VS. Neocortica~l Lesion 20.29"

Sham~ vs. HipIpoco pa~l Lesionl 13.92:"

Neocortical v;. Hippoc-:?ral Lesion 0.23




Acquisition vs. Rev`erssl 19.77-~


Neocortical Lesion

Acquisition vs. Reversal 0.01




Acquisition vs. Reversal 2.30


i'p<.01










DISCUSSION


This study examined the performance of sham, neocortically, anld

hippocaupally losioned rats in the a~cquisition and reversal of a two

manipuland a ifferentiastion as affected by certain magnipulations of

response-rzinforcem`ent contingencies. For one-half the shes, neo-

cortically, and hippc 11yll lesion~ed Ss, these manipulations insured!

that each S e-itted an equal number of reinforced responses on the

twro manipulanda1 durinQ a complete experimental session. As a result

of this procedure, each S_ also emitted twice as -many non-reinforced

responses on one ma2nipulantumd (the FR 9 manipu~lcaduo as on the secondl

(the FR 5 manipulanudum). For the remaining Ss, the experimental

manipulations insured that each S, saitted an equal number of non?-

reinforced responses on the tw;o man~ipulana during a complete exp~er~i-

mental session. As a result of this procedure, each S emitted twice as

many reinforced responses on the FR 5 nanipulandun as on the FR 9

manipulandum.

The Douglas-Pritram theory of hippocampal function (Dougalas &

Pribraml, 1966; Doug~las, 1967) is a vigorous attcnpt to integrate the

wide variety of behavsioral changes following hippocamal disruption,

and leads to clear-cat predictions of the behavioral effects of the

mninpulations performed in this study. Specifically, the theory

predicts retarded acquisition and reversal in hippocampal Ss wihen

compared to sh-3 and neocortical control Ss under the treatment condition

which specifies eqluation of the number of reinforced responses emitted









on the t"o I -nipulln less or no retardation in hil~? I : Ss

under the condition which served to eqjurte the nuator of non;-reinf~orced!

responses e-itted on the discrimin-nda, and, indirctly, no difference
bet::een sh-1 and neocortical Ss under either; of these two treatr,-nt

conditions. These predictions are contradicted by the results Of this

expericant.

The trials to criterion data12 do ot revell an differences

between the7 three lesion grorps in acquisition performance. This

finding is in geneDral accord with the results of recent studies of the

role of the hippocampus in discrimination learning. However, such

studies have not extn~led the effect of differential densities of

reinforced anrd nson-einforced re: 1 '0a to th~e alternative discrin-

inanda upon discrininstio3: leering in hioptcentactoniized Sj. The

prcsont findings, alth~ough inconsistent with predictions derived froni

the Doug~,las-PrTiibran codel, inticate thant such differences have no sig-

nificant effect on acquisition peri'o ice in either sham, neocortically,

and hippocam-pally lesioned Ss.

The performance of the three lesion groups .in reversal also is

inconsistent with predictions derived from3 the Douglas-Pribran. for,

as in acquisition, the two response-reinforcement contingencies do not

differentially affect in either sham, neocortically, or hippocanpslly

lesioned Ss. In addition, the reversal data appear to be inconsistent

with the bulk of the data on the performance of hipipoca~Dctactoize and

control Ss in discrimination reversal; nanely the hippocamipally lesioned

Ss are typically reported as retarded in discrimination reversal

when compared to neocortically lesioned and shan control Ss wiho usually







do not differ fror: eachn ot::-r. The results of the present study indicate
that it is neecortically a=d hippoc~anpally lesioned. Ss whoe do not

diff"er from each other, and: both appear facilita~t~ed hen compared to

sham~ operated Ss on the trials required to attain criterion in reversal.

A compa-"rison of the ressio-- to criterion d,-ta with alternative p~er-
formance meaasreso, silch as trials to successive criteria and the ab-

solute per cernt of FR( 5 responding for successive days, revealed that

all three meoorres depictel acquisition and reversal pesrformance in a
similar fashion~.

A possible explanation of this disparity is offered by thle
relationships htweern a~cquisition and reversal perfomrmace as revealed

by the Spear~-a rank order correlation coefficient. The she operated

Ss, who require a significattl y greateT ~r atier of trials to attain
criterion in reve-rsal when compared to the neocortically and hippo-

campally lesic::sa9 Ss as indicated by the Studentized range statistic,
are also the 53 w~ho manifest a significant inverse relationship between

trials to crit~erion in acquisition and reversal. In addition, a greater

number of Ss in, the sham control group attained the criterion in 11 or

less sessions (415 of 20 Ss) than in either the neocortical (11 of 20

Ss) or hippocampal (12 of 20Ss) lesion groups. When the three lesion

groups are pa"rttioned in terms of the response-relinforcement con-

ting~encies, si,:ilar phenomm~a are observed. These findings suggest
that some Ss pos~sess an initial position preference which, when in

accord vith thei requirements of the initial differentiation, facilitates

acquisition ami retards r~avrsal. Moreover, it appears that a greater'

proportion of ES in the shes operated group fall into this category









tha~n in either of" the t-o o~t of lesioa Groupt. It r ; be myactli, then,
that the poorer perfortance ol the s!: I control Ss in rev:ersal is an arti-

fact resulting7 fro-. a failure to copletlcelyr control for initial position
preference, and thcrt if this brd been dorne the~ dliferences btsetwoo the

three lesion groups in reversal would be elinii-ted.

The exper~iaental proceaures e ..plok-ed in this study differ in a
num~ber of details froa those in which hippoc 21n~ lesion-irngced deficits

in discrinination reversal. are coclonly obseruel. It is possible that the

lack of a lesion-ind~csci deficit in the presented study may b e ttributable
to one or care of those differences. One s~uch modification involves the

utilization of an oiertreinides procedure f~oll0:irg aettinaent of criterion

in acquisition. IlurestiS ticols of thr cEfecL o. 3:tz ini : u~on r 1~n in

the T-rt-ze indic to thrat Ss subjected: to, o:: the wEpr.e a at least 1.3

(Macintosh, 1962) and 3 (Publes, 1956) ties cs manyr overtraining trials
as were required to p~reac criterion in the acquisition of a discrimination

perfor; better in reversal thar Ss without: oertrairning (the overtraining
reversal effect). An exenination of Rteid's (1953) data indicates that w~hen

overtraining involves less trials than vere required to attain criterion the

overtraining- reversal effect is not seen. It is difficult to compare those

procedures and the present one, for different responses and procedures were

employed. However, since this study coployed only one-half as r-ry over-
traininga sessions as w~ere required to attain the acquisition criterion it is

unlikely that the overtraining reversal effect was operative. Despite this,

an examination of the overtraining reversal phenomenon does add to an under-

standing~ of the results of this study.

Macintosh (19i65) notes that it is presumably justifiable to

regar~d reversal learning as consisting of two parts: (a) extinction







of a tendency to select the for,:er S and (b) acq~uisition of a te-rdoney
to select the newl SD. Stage (a), extinction, is usually regarded as

continuing so long as S scores below chance level, and stage (b),

acquisition, is typically depicted as comencing as soon as S begins
to perform above chance level. It should be noted tha~t icmplicit in
the formulatic= describe-d by Mazcintosh is the generallyr accepted

assumptionthat learning is a conitinurous, rather thann discontinuous,

process. Whethrp this is indeed the case has not yet teen completely
resolved. The present discussion is concerned priczrily with the
effect of atte-ntional factors upon discrimination reversal rather than

with the und-erlying nature of the learning process,

It is ofteni rePorted th~at ovesrtrainir; of a run::aiy response
results in reduced resistance to extinction ('Jagner, 1963). It is

logical to assue, therefore, that this phenomenon is what underlies
the overtra~inir= reversal effect; nac~ely, overtrainin,- facilitates
extinction of responses to the former SD in thie formulation described

by liacintosh. This is not the case, however, for overtraining in the
discrimination paradign regularly increases resistance to extinction

of responses to the former SD (Macintosh, 1962). As M~acintosh (1965)

points out, overtraining facilitates reversal of a simultaneous dis-
crimination not because of, but in spite of its effect on extinction.

This finding vould appear to negate an extension of the frustration

(lawrence &~ Festing~er, 1962) and generalization decrement (Kimble, 1961)

explanations of extinction to the overtraining reversal effect and,

by implication, to reversal training in general.










Harcintosh (1965) reports that existent evidence indicates

overtraining- facilitates reversal by shortenin3 runs of incorrect

responses durite the middle of the reversal. This su~gests that over-

traininG reduces Ss' tendencies to respond to irrelevanlt cues during

reversal. Thier-e are two possible explanation. for this: Either over-

trainin3- effectively enables Ss to "adapt out" cues along irrelevant

dimension~s; or ovr-training allows aaple opp~ortunity for Ss to learn

to attend to the relevant cue dimension. IMacintosh presents evidence

which indicates th-t it is the latter alter~native which underlies the

overtraining- reversal effect, and points out a distinction bstwieeni

research utilizing visual and spaztial cues. Strdies whichl have in-

voilved a, sinuilt,-neou~s visual disciulination (b-rightnes~s, yttern, etc.)

invariably prodiuce the c-;ertraining revr-iSal effect, while those

studies which employ a spatial discrinirationl (left turn versus riCht

turn in TSand Y--azes, etc.) frequentlyr do not. A rcajor reason for

this, Vacintosh contends, is that the~ rat (the commonly used experi-

mental organism) is prlrcarily spatially oriented and, as a consequences,

spatial cues have a high priority even without overtraining. Since the

rat is already attending mainly to spatial or position cues, over-

training would not be expected to have much effect on perforeance in

reversal. Conversely, the lower the relevant cue dimension is on the

Ss "attending hierarchy," the more valuable overtraining vould be ex-

pected to be in firmly establishing the relevant cues in a position of

dominance. The nagnitude of the overtraining reversal effect should be

inversely related to the probability that S vill attend to the relevant

cue at the beginlning of discrlimintion training, and to the number of

irrelevant cues involved in the discrimination.







The preceding dirzussion is carkedcly similar to the Douglas,.
Pribram concepItulization of the role of the asygdaln in discrimination

learning; n~cely, the registraztlio of the effects of rein~forcement or,

alternatively, the direction, of attention to the aspects of the tasl;

(relevant cues) associated wiith reinfoarcemnt. Holwever, the above
form~ulation of the functics of attentional factors in discrimination

learning does not incorporate a process analogous to that attributed to

the hippocrrpass; the eating out of stic~uli associated with non-reinf~orcel

ment. It will be recalledhat ai2* n alternative to thle attentionall

nodel indica~tes that the ovjertrainin~g rcevesal effect can~r be attributed

to the opportu lity for SS to effectively ''ad-pt out" irrelevant cues

(Spence, diescaiibed in M~acintosh, 1965). Perhaps an explanat-ion! of the
overtraining ~-reersal effect involves both these proce~sse. The

Douglas-Pribr;- model sugge-sts that this is so. In a~ddition, the
results of thiis study may +ct be as inconsistent with thle Doublas-

Pribras model as ~a~s first indicated. The differentiation required in

the present stud involves spatial cues, a dimension thought to be highI
on tbe rat's "aittentional hi~erarch~y." If this is the case, the role of

the hippocaiusgh that of ga~tingR out irrelevant stimuli, would be

minimal in thE, intact S, and Ss without the hippocampus should not be

greatly impaired. Perhaps a bippocampacl lesion-induced deficit would

be evident in the present rarad~ig if a ta~sk involving a non-spatial

differentiation, or, more probably, a differentiation between a large

number of eq~ally salient mes was employed. Support for this possi-

bility is provided by Pribra (1969), who reports that haippocanpctonized

mconk-eys shoM retardation in discricmination learning, provided there are









a large number of non-re::ar~ie alternatives in the s~ituetio~n



A second procedlural innovation employed in the pl aet study

involves the response selected for study. Those studies, reported

previously, whiichi Inve demonstrated the hippcarpal lesion! reversal

deficit ha~e typically e-?loy~edan instrumental response requiring

some forn of gross loconotion1 on the par~t of S. In contrast, this

study utilized an operant response, a bar pre3S, which,) unlike thle

typical instru~ental response, requlires 8 dr i 7:B Of loco:ation, tak~es

a short timea to execute, requires relatively little effort, Eand leaves

5. in thle same pl c-e r-sdy to respond again. Although it is generally

as,~uned thati the behe;;iolral principles an~d ne:!rophy~sioloGical reche-

isrms underlyin= rvbt appear to to anazlogous task;s in the two experi-

mental approaches do not differ in any critical aspect, a thorough

comparison of these tw~o p~rocedures; has not yet been. attempted. However,

a recent study by Means, Walk~er, and Isatcton (1969) indficates tint the

effect of hippoco'9pal disi~rution upoon go-no go performance mcy be

response-specific. Although it is typically reported that hippoceapecto::y

interferes with this behavior whien exam~ined in an instracental perraii63,

such as an alleyway (Brown, Kaufcan & Hasrco, 1969), M~eans et al. report

that hippocampal ablations facilitate per-fomance in this task when a

bar press response is utilized. Findings such as these question the

trans-situational nature of the pattern of behavioral disruption ob-

served following hippocaepl destru~ction and, consequently, any formu-

lation which attempts to account for these effects with global concepts







Such as 'perseveration,"! "6gating," or "inhibition" without further

refrinement or qua~lificatin.k

The third r:-jor difference betwooen this and contemporary in-

vestigaztions of^ the- role of the hippoca~pus. in discrinination learning

involves the schedule of reinforceloent associated with the tw-o to-ba-

discriminrated responses. The research reported previously hazs typically

provided cont-nuous reinfo:: :ae t for "cor~rect" responses and writhheld

reinforcement f~or "incorrect"' responses. In thez present study con-

curfrent ope~rans were utilized: Both responses were reinforced, one

on ian FR 5 schedule and th~e other on an PR 9 schedule, and the forn-

ation of the discrimninatio~n was based on a relative, rather than

absolute, diffecrential in! 1einf'oi~rceaent desity. The experilental

anarlys-is of cocuc~rrent rattio schediules indlicates t'-at withi unequl FR

requirlements, respoding tends to be rlintainedt only by the schle~dle

with the smaller FR requnir;ent; with equal FR requirements, responding

can be maintained by either one, and shlifting fromi one schedule to

the second occ-rsionally occurs (Catania, 1966, Herrnstein, 1958). In

a study which is only superficially corwarable to the one reported

here, DougEla~s and Pribram (1966) examined the effects of probabilistic

reinforcement upon the for;3ation of a discriminated panel press in

mor3keys. As inl the present study the discriminationl rested upon a

relative differential in reinforcwe.2e density; one response was

reinfocced 70$ of the time and the second reinforced 30i0 of the time.

Their results, in contract to those of the present study, indicated

thact hippocampectomized Ss are ret~ared with respect to control Ss









in their ability to acquire a discrilinetionl u~icer such coalitions. Un-Y

fortunartely, no dataarepresented on the performance of these Ss in

discrininartion reversal. The reasons for these applrently contradictory
findin,-s are unlmoun, but these studies rev;eal that insufficient

attention has been directed towards en claboration of thie effects of

schedules of reinforc;--ent on discricnainion for ion andl rcrersal

in hippocengctorlzed S~s.

Another difference between thi~s andj other studies of hrpippcnipal

function involves the specing- of test trials. M~ost research in this

area bets exployed a discrete trial proc "m, a 4~ the re~lated technlique

of massed trrinity trills during~ each 0 lg eob .1 1- 1. session. I

the present stirdy the equiwlr"ei t of^ toot trials, the fiLve rinule free-

chloice periods, w~ere widely spasced for theyJ occur-red at the beginning
of' each daily experimental session. No direct evidence is available

concerning the effect of this factor on discricination learningr and
reversal in hippocampectomized Ss. However, there is evidence th-t the

interval betu:cen trials does influence the behavioral effects of hippo-

campal disruption. As reported previously, Kirkby, Stein, Kinble and
Kimble (1967) have demonstrated that the lack of T..aaze spontaneous

alternation commonly reported in hippocom-pal Ss can be reestablished by

leng~thening the intertrial interval from 50) seconds to 10 minutes.

Although. their exrplanation of this phenonenont, a postulated lesion-

induced reduced information acquisition rate, has been generally

abandoned on the premise that such preparations do not show deficits in

a number of alternative learnine teaks, no adequate cirplanation hats been







foi-ulated?. Little or no adlditiolal research has beesn directed tol!ards

an un~derstar~ding of this finding, and until this phenomenon is investi-

gated in greater detail such. an erolanaztion of thre results of the

pr-esent expericient cannot be fully evaluated.

A fifth ncjor departure of this experiment relative to previous

ree~serc is the utilizationl of a forced training technique. As a

function1 of fulfilling th~e requirements of the re~sF~pose-roinforcem~ent

contingncies, this procedure insured that each S was fully exposed to

the conditions of rein~for~ceaent throughout both acquisition mid

reversal training. In addition, it can be assumed tht1 this innovjation

mo;t. proba'oly tpzintained the strength of the FR 9 response at a

relatively highe-r level thns discrimiiation. studies which have not

employged forced training on!, and reinforcamecnt 08 the "incorrect"

response. Isaacson, 01ton, "luer and Start (1966) present evidence

wJhich indicates that the hippocampa~lly lesioned _S's inability to

withhold a response in thle passive avoidance task is directly related

to the strength of that response. It is also possible that the ease

wLit which hipp0cauipctomized S~s can inhibit one response and initiate

an alternative is dependent upon the relative strength, or probability,

of those two re~sponses.

These findings, which demonstrate that hippocam~pal Ss are

capable of inh~ititing an established response and initiating another,

strand in markred contrast to the bulk of the data on the performance of

such Ss wrhen feced with similar tasks. It is not surprising that task

Variables, some of which have been discussed above, have the potential

to profoundly influence the behavioral effect of physiological manipu-

lations. What is surprising is that no concerted. effort has been made









to explain such fjitin:G; withinn the conto::ts of prscriit for u`lations

of hippoca.;1 ft:!ction, or to revise theje for:.11stions so thst theyj

ma3y incorporate these results. All too often fictings suchi as have
been disculssed. here are neglected or dismissed as aberrent. PerbyIs a

detailed crvliation of the never in which Fconcillental erulipulations

can change or counteract the effects of physiological m:nip.11aions will

provide increazsed insight into the role of neulrophyisiological systels

in the intact org:Ris-.

The unexpiected facilitation of discrkrinnition r:..: al per-

forcnnce resultin,- fro= the neocor~ticcal d-legfe sstained by the

control Ss, is ecost likely attributable to uncontrolled p siti~on

preferences, a~s et- deiscused prcviously. Oth-r Eielpei:: ente tion on ti-

effects of hippoc?-:.1 ablection hasj typically looked i alo ous n~eo~-

cortically lesioned control Ss, an~d hns refularly; reported that such

Ss do not differ from their u3Fnoperaed ouilteryrts. There are ex-

ceptions; to this ho-ever, for Meanls, -et al_. (1969) here found that

destruction of the noocorter1 overlyir~e the hipp~ocenpus leads to a

retardation of performance in the go no-go task;; and 01ton and Isaacson

(1967) have reported thazt da-inge of this area, as uell as this area

plus the hippocampus, lengthens response latencies in avoidance and

escape tasks.

In the present experiment neocortical destruction involved

considerable portions of the rat neocorter comparable to Broadr~an's area

7, which is involved in somesthesis, particularly the integration of

information on eight and the state of muscles and Joints; areas 17








and 18, the Tinal3 projection and association reles, respectively;

area 25, the entorhiral cortex; and area 37, which receives conesthetic

and optic association fibers and, in can1, is thought to be involved in

the recognition of body inge, individuality and continuity of"

personality, sad of the self in relnation to the environment (Kreig,

1957). since a considerable portion of the hippocatral research has
involved sode- damage of these areas it is possible that comonly ob-

served hippocampal lesion deficits are in actuality a function of an

interaction of the hippoca-npus and the neocor~tex whzicht overlies it.

Within this context, Douglas (1961) ha~s observed that electrolytic

lesions restricted to the 11 3c~i~ fr~equently do not produce the

deficits seen in ablation stud~ies: involving neocortical destructiol.

It is also possible thiat the facilitated. performance shown by the

hippocaopectomized Ss in the present study is fully accounted for by
the effects of neocortical destruction. Questions such as these point

to the relative prinitiveness of our understandingp of the role of the

hippocampus in bhav~~ior, and to the importance of further research in
this area.













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BIOGRAPHICAL SKETCHI


Miichael Arnold Mlilan wavs bor on January 25, 1938, at Newl York,

NewI Yo~r. He attendied public school in Hewr York stzte and graduated

from Pay~etteville-':an~lius High School, Payetteville, Niew York, in

June, 1956. In May-., 1960, he received the degree of Eachelor of Arts,

fron Syracuse Universi~ty. From 1960 until 1962, he served in the

Adjutant General Corp~s of the United States Army. Following his release

from the Arn-iy he waes elployed a~s a psycho.logical research assistant

with the Veteran's Adinirstration Easpitc1 in. Syracuse, Kel; York. In

September, 1963, he enrolled in toe grandnate school of the University

of FloriCda andc received the Malster of Arts degree: in December, 1965. Be

served as a research assistant for Dr. HI. S. Pennypackier and as an

interim instructor with th~e Departrant of Psyrcholoy while ratriculating

for the Doctor of Philosophyl degree in psycholog-y.










This Sdisseration wans prepared under the direction of the chair-

manu of the ca~nidate's supervisory comsittec and has been approved. by

all memb5ers: of that: committee, It was submiitted to the Dean of the

Coljego of Arts andi Sciences and to the Graduaite Council, and wasF

apyproved aes partial fullfillment of th~e requ~irements for thel dclree of

Doctor of Philosophy.


Jun~e, 19?0




7 7, ciences









Superv~i cry aStttee












ACQUISITION AND REVERSAL OF A TWO MANIPULANDA
DIFFERENTIATION IN SHAM, NEOCORTICALLY,
AND HIPPOCAMPALLY LESIONED RATS










By
MICHAEL ARNOLD MILAN












ADISSERTATION PRESENTED TO THE GRADUATE COUINCEL OF
THE UNTYERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY


UNIVERSITY OF FLORIDA
1970













ACKNOTiLEDDDETSS


I graPtefa~lly acknolledge the support and direction provided by

Dr. H. S. PennypaScker both in the execution of the present project

and, more toportan~tly, throughlout my graduate career.

I also express Gjy apreciation. to Dr. Robert L. Iteacson,

Dr. Frederick a. King, Dr. C. Mlich-el Levy, an~d Dr. Vlilse 3. Webb

for their assistance in the development. of this dissertation.

I thank Mirs. Pauletta Slrders and Mirs, Gloria Srmithi for their

histological assistance, atnd Mfrs. Irom Smith whlo abcly type~d the

present rmrnscript.












TABLE: OF' CONTENTS


Page

ACIGT:OWLEDGG~~IZE!TS..............**.. ****** 11

LISTOFTAhLES. ................... ..... iv

LIST OFFIGURES ................... ..* T

ABSTRACT ................... ......*** v1

INTROlUCTIION. .................********** 1

METHOD. ......,,..,,........ .......... 14

RIBUTLTS.................... ......... 24

DISCU~SSIarl...................*********. 47

RZERENCS. ...................... 60~

BIOGRAPElICAL SKET~iCH .. .. ... . ... .. . . * 67












LIST OF TA3BLE


Table Page

1. TRIAL.S TO CRITEROIO IN A.CQUISIT'IOI P!: RIERSSET FORi
SHAMI, NiEOCORTICHTLY, BMiD H(IPPOCOPAL~LY L510:1ZD
Ss ASSIGNE TO THE: REIiFORC3D RLEPO::SB EQATED
COcnDIIOa. ................... .. 27

2. TRIALS TO CRITIl0N INi ACQUIISITION: ~D RME~SAL OR?
S~In, NEOCORTICALY, ID HiIPPOCA"PALLY LESIOlil
Ss ASSIGLED3 TO TH2 01:C-33IFOR.1CED) ISPO~iS"S EQUATED
CONDITION. ................... .. 28

3. SPilLIMI RAH; ORDERa CORWEA~TIONI COERICIE'TS (r ) FOR
SHMI, NZCORTICAL~, DiD HIPPOCCLAL IESIONI GDUPS . 30

4. SPEARLAN RC~ ORD32 CORCIAIOU COLIFICIZ.-?S (r,) FOR0
SIW1 B3OCOiICE, AND E.IPOCi'PALT LTTION GRO~UPS
UNDER E-UATED :iICIE033023 IOR 20-RZI;20RCED
RESPO:-DING aIRING TRAINING .. ... .. .. .. 31

5. ANEYISIS Or VAR~IAcZ on TRI~lS To CRITERI~ON .. .. .. 37

6. h';ALY~SIS OF" 7RIARCE 011 SQUA~RE-ROO TRIANSIORATION OF
TRIALS ~OCToca aor. ................ 38

7. STiJDMITIZED PiEGE STATISTIC A POSTERIOJ TESTS. . ... 45









LIST OF FIGIGES


Figure Pa

1. Tracings of representative cross sections through the
hippocampal lesion. ... ............

2. Tracings of representative cross sections through the
neocortical lesion. .................

3. Number of sessions for Ss in eachl lesion groupr to attain
criterion in acquisition: Reinf~orced responses
equated ................... ....

4. NTumber of sessions for Ss in each lesion group to attain
criterion in reversal: Reinforce: responses
equaed............ ...........

5. Water of sessions for ss in each lesion group to attain
criterion in acquisition: Bon-reinf~o-ced responses
equated ................... ....

6. Number of sessions for Ss in each lesion group to attain
criterion in reversal: Nion-reinforced responses
equated ................~.......

7. Cumu~lative percentage of ES in each1 lesion condition
attaining criterion in successive 5 session
blocs........................

8. Cuculative percentage of Ss in each response-reinforce-ent
condition attaining criterion in successivie 5 session
blocks. .... . ... ... .. .. .. .

9. Cumulative percentagel of Ss attaining criterion in
acquisition and. reversal in successive 5 session
locks. . .. .. .. . .. .. . .

10. Cluoulative percentage of Ss in each lesion condition attain-
ing the acquisition criterion in successive 5 session
bloks.. .. .. . .... ... .. . ...

11. Cupmlative percentagee of Ss in each lesion condition
attaining the reversal criterion in successive 5
session blocks. .. . .. . . .. .

12. Mean trials to criterion in acquisition and reversal for
Ss ineach lesion group .............. *










Abstract of Disser~tation Pretentecd to the Graduatee Counacil in
Partial Fulfillmient of the Requirirents for the De,-ree of
Doctor of Philosophyi at the University of Florida


ALCQUISITIONJ AND R2EiESALr OF A TWO RAI~PUIANDA DIFF~IER:TITIONj IN
SHAM, NEOICORTICA.LY, AND HIPPOCAMPALL LESjIONED P,1TS


Michael Arnold Hiilan

June, 1970


Ch~airman: E., S. Pennypa~ckr
MlaJor Dealrtment: Psychology

Sham, ne~ocortically, and hiI~ppocpaly lesioned. rats were exr-

amined in the acquisition of a two an~ipuilana different~iation imrder

conditions which insured that either the absolute number of reinforced

or non-reinforced responses each S elitted on ech renipulandu2l during-

each expTerimental session were equasted. Acquisition performance was

not differentially affected by the thnree lesions, nor by equated

reinforced or non-reinforced responding. Reversal performance did not

differ for the neocortically and hippocampally lesioned Ss, but both

appeared to be facilitated when comparedl to shamn control Ss. As in

acquisition, equated reinforced or noa-reinforcedi responding: did not

differentially affect perf~ormancea of the three lesion groups.









INTRODUCTION


The hippocampus, nestled in the inner folds of the temporal

lobe, has been subjected to more intense experimental investigation
within the past decade than in all previous years combined (after

Douglas, 1967). The early neuroanatomical investigations of Papez
(1937) which first linked the paleocortical structures of the rhinen-

cephalon with e-ctional behavior were supported by the contemporary

experimental investigations, performed by Kluver and Bacy (1933), of
the effects of temporal lo'osctorny on behav-ior. MacLean (1954, 1955,

19571 1958) for;alized this orientation, postulating a dichotomy between
the phylogenetically older paleocortex andl the more recent neocortex.
The former was presented as involved in. a~variety of emotional and

visceral functions, whiile the latter was thought to be concerned with

more cognitive functions. However, as the hippcampus wras subjected

to more intense experimental investigation a more complex picture of

hippocampal function emerged. Before summarizing the results of more
recent investigations of the role of the hippocampus in behavior and,

concurrently, reviewing the physiological theories of hippocanpal
function which have emerged from those data, a general description of the

hippocampus and its' interconnections with other brain structures will
be provided.

The hippocamipal formation, composed of the hippocampus (Ammon's

born), the hippocampal gyrus, the fascia dentata and. the fornix,11es along
the medial and ventral border of the temporal lobe where it is wrapped










around the posterior surface of the thalanlus. The hippoceapurs,

reminiscent of the coincon sea horse Einocannusf hingang from which

its name is derived, is the major struecturl c:;lponent of the hippocar:pal

formation. Gross description of the hippocam~pus was provided by Lorenlte

de rHo (1934, cited in Doug-las, 1967) who divided it into four segments:

CA1, located proximal to the subiculua, CA2, CA3, and C~E., lying in t~he

fold of the granuls cell layer of the fascia dentata. The most generally

accepted cytclatchitectonic description of the conplex internal structure

of the hippoca~mpus was provided by Ca~jal (1955). starting from the

ventral surface above CA2, theaproceeding vertically, seven rajor

layers are evident: the ventricular ependyca, al~eus, stratus oriers,

stratun pyranidale, stratlu radiul, stzatul lacunosun, andi strata~

moleculare. A! detailed exposition of the internal morph~ology of the

hippocamuns and hip~pocacpl;~ formation is provided by liaissner (1966).

Twso major afferent pathwayrs serve the hippocampus: the alrear

path through the fornix system and the perforanlt pth through the subicu-

lu.The fibers of the fornix arise primarily in the septal area anl

the intralaaminar nuclei of the thalamus (Green &; Adey, 1956). The

system is more involved than this, however, for inputs also reach the

hippocampus from the ascending reticular activating system of the mid-

brain and thalamus (Green &z Arduini, 1954) and from the hypothalauus as

well (Feldman, 1962). The perforant path reaches the hippocampus by way

of the entorhinal cortex and subiculum. The temporoamionic tracts passs

from the entorhinal cortex through the subiculum to the hippocampus

proper. The entorhinal cortex, in turn, receives its efferents from

considerable areas of the neocortex (Green, 1964). In addition, there is








evidence for direct fibers from the cing;ulu attaining the hippcamput

via the perforant pathway (Adey, 1961).

Fibers passing into the finbria constitute the main efferent

pathway of the hippocom~pus. These fibers cross to the contralateral

bippocampus via the hippocampzl commissure, or enter the fornix and

project variously to the septum, hypotbalanus, anterior thalamus, and
rostral portions of the brain stem (Green & Adey, 1956). The hippo-

camus also gives rise to efferent fibers to the entorhinal area via

the temporoamonic pathwa~y. In addition, Gloor (1960) presents evidence

for primary hippocam.po-rt yedaoiao d fibers as well as secondary anygdalo-

hippocam~pal connections. Aen intensive review of the literature pertain-

ing to the neuroanatomical investigation of the hippocampal aff'erent and
efferent sys~te-s may be found in Green (1964) and Stumpf (1965).

In an attempt to assess the contribution of the hippocampus to

the physiological substrata of behavior, researchers have examined the

effect of hippocaapectogy upon a wide variety of behaviors. One of the

most studied classes of behavior falls under the general notation of

avoidance conditioning. Interest vac sparked in this paradigm by the

relatively early study of Kimura (1958) wiho found that rats with bilateral

posterior hippocampal lesions were deficient when compared to neo-

cortically lesioned and shaml operated subjects (Ss) in their ability to

vithold a well-practiced, food motivated approach response followring the

introduction of punishment (electric shock) of the consumatory response.

The essential characteristics of this experimental paradigm are proto-

typic of what is generally referred to as passive avoidance conditioning.

Such deficits in passive avoidance have since been replicated under




Acquisition and reversal of a two manipulanda differentiation in sham, neocortically, and hippocampally lesioned rats
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 Material Information
Title: Acquisition and reversal of a two manipulanda differentiation in sham, neocortically, and hippocampally lesioned rats
Physical Description: vi, 67 leaves : illus. ; 28 cm.
Language: English
Creator: Milan, Michael Arnold, 1938- ( Dissertant )
Pennypacker, H. S. ( Thesis advisor )
Isaacson, Robert L. ( Reviewer )
Levy, Michael ( Reviewer )
Webb, Wilse B. ( Reviewer )
King, Frederick A. ( Reviewer )
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 1970
Copyright Date: 1970
 Subjects
Subjects / Keywords: Learning, Psychology of   ( lcsh )
Rats   ( lcsh )
Psychology thesis Ph. D
Brain -- Localization of functions   ( lcsh )
Dissertations, Academic -- Psychology -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Abstract: Sham, neocortically, and hippo car.pally lesioned rats were examined in the acquisition of a two manipulanda differentiation under conditions which insured that either the absolute number of reinforced or non-reinforced responses each S_ emitted on each manipulandum during each experimental session were equated. Acquisition performance was not differentially affected by the three lesions, nor by equated reinforced or non-reinforced responding. Reversal performance did not differ for the neocortically and hippocanpally lesioned Ss, but both appeared to be facilitated when compared to sham control Ss. As in acquisition, equated reinforced or non-reinforced responding did not differentially affect performance of the three lesion groups.
Thesis: Thesis - University of Florida.
Bibliography: Bibliography: leaves 60-66.
Additional Physical Form: Also Available on World Wide Web
General Note: Manuscript copy.
General Note: Vita.
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Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000565821
oclc - 13586206
notis - ACZ2241
System ID: UF00097730:00001

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ACQUISITION AND REVERSAL OF A TWO MANIPULANDA

DIFFERENTIATION IN SHAM, NEOCORTICALLY,

AND HIPPOCAMPALLY LESIONED RATS










By
MICHAEL ARNOLD MILAN


A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY













UNIVERSITY OF FLORIDA


1970




















































'JrJr. ERS T r' F:* L F RIDA


3 1262 08552 4113












AC-f ',U`..1_ -. .- :TS


I gratefully t 1 -.,. le: the support and direction provides by

Dr. H. S. Pecrnn.:-c. both in the E; '.;.tiOn of the present project

and, ~,o e iportantly, thiou3' _it ny granite career.

I also express y appreciation to Dr. Robcot L. Ilc?.cson,

Dr. Frederick A. King, Dr. C. Michlel I' ;, and Dr. Wilse B. Webb

for their assistance in th2 devaloccant of this dissertation.

I thank Hrs. Pauletta 3--.::ra ari Mrs. Gloria S:mith for thcir

histological assistance, andi Mrs. Ira Snith who ably typ-d the

present riuscript.










TABLE OF CO :.:.T3


Page
ACKNO'TL z-:E-- f .. .... . .. .... . . .. i

LIST OF TTLS . . . . . . . . . . . . iv

LIST OF FIh.- . . . ........ . . v

ABSTRACT. ................ . .. vi

INTRODUCTICO:. . . . . . o ..* . . 1

METEOD. . . . . .. . . . .. 14

RESULTS .. .. .. .. .. ..* .. ........ . 24

DISCUSSION.. ... . ........... .. 47

PRz-c C3. . .. .. . . .. .. ......... 60

BIOGrHICAL S::: *; ........ . ..... . . .a 67
























ill












LIST OF TA-LL3


Table P-e3

1. TRIALS TO CRT TTRIO IN ACiJSITT(r A'D PCR TrST, FOR
SEAM, -.' 2CTICALT., AiTD HlPPOCX:0 PALLY I:: IO:D10
Ss ASSIC .TO T E R21,n1O;C, 3 1.- :0SZ3 I .'D
cc" -i ( . . .. . . . .. . . 27

2. TRIALS TO CRITZ IO IN ACQUISITION A. D R-4? P5TAL FOR
SEA:, NEOCOYTICA.LY, AD EIDPPOCA'TALLY LESIO3ZD
Ss ASSIGCI TO TH~ ::.;-.. :i.:OCaD 01533 EqUATED
COL.TIO . . . . . . . . . . 28

3. SP'1 ..... P.'.... 70,,,R COR2r2ATION 0'C0 ICi .."?1 (r,) KOR
SHAM, ". TIiLC, y-iD HIP2POPC-'-, LZ3ION L... 3 . 30

4.. SP'... 2,,- R : O.- 2 COijL..L i0: C'* ICl l-i- (rs) %R
:S'+A2, :..3....IC.., ND rIPOC7r2?AL LiSIO: G OUPS
).;^A --:..-._) R:+I2'ORC3D OR N01-.R-0. -ORCED
.J .'i DU I:.T TRilIG . . . . . . 31

5. ANALYSIS OF VARIA TCE ON TRIALS TO CRITICC, . . . 37

6. ANALYSIS 073 VA''IC 0:C 7 " -.7-' TA-S OPTION OF
TRIALS TO CRI:0- . . . . . . . . 38

7. STUDL:,?ZID PR..E STATISTIC A P,.'. IO' i TI.S. . . 46








LIST OF FIGcURIS

Figure Page

1. Traci"-'s of representative cross sections through the
hippoc::;.1 lesion. . . . . . . . . 25
2. Tracings of representative cross sections through the
neocortical lesion . . . . . . . 26

3. N'-:ber of sc:sicr; for Ss in c:m' lion g:c-,p to attain
criterion in acquisition: ReiL:C.orced responses
equated . . . . . . . . . . . 32

4. 2nter of sessions for Ss in e.-ch lesion group to attain
criterion in reversal: R:ir.Corced responses
equated . . . . . . .. . . . . 33

5. ,N-etr of s:.-:lo.:: for Ss in each legion group to attain
criterio:n in acquisition: ...-rclnforce re:~ ones
equated . . . . . . . . . . . 34
6. Nu-:i'r of sessions for Ss in each lesion groups to attain
criterion in reversal: .:'.-reinforce. responses
equated . . . . . . . . . .. 35
7. C',3.-tive percentage of Ss in each lesion condition
attaining criterion in successive 5 session
blocks. . .. . . . .. . . . . 39

8. Cunalative percentage of Ss in each re.'ss'-reinforcesrnt
condition attaining criterion in uc-.csive 5 session
blocks. . . . . . . . . . . . 40

9. Ciurlative psrcezntage of Ss attainirn criterion in
acquisition and rLv-erzal in successive 5 session
blocks. .. . . . . . . . . .. . 41
10. Cumulative percentage of Ss in e-ic lesion condition attain-
ing the acquisition criterion in successive 5 session
blocks. . . . .. . . .. . . . 43
11. Cumulative percentage of Ss in each lesion condition
attaining the reversal criterion in successive 5
session blocks. . . . . . . . . . 44
12. Mean trials to criterion in a:quoisition and reversal for
Ss in each lesion group . .. . . . . 45









Abst'rct of Dissertatioa Presented to the Gtr>uate C-.' -i in
Partial ualfinl-ent cf th3 Rcquirm:ent. for the Dir:ec of
Doctor of Philosophy at the University of Florida


AC:.iI.-ITION AND RE7V'.. OF A l..1 MANIPU DA Di ATIlON IN
SH:. :, 2 :W)CORTICJLLY, A!iD HIPPOC'AALLY LZSIOJISD PRATS

By

Michael Arnold Milan

June, 1970

Ch'aI ,-,n: H. S. P eny '-
Major D treatment: Psychology

Sham, ncocortically, and hbippoca.pally lesione.C rats voer ez-

a-tI:~ in the a::-. 1itito:I of a tvo 1nil-.)a diffc tietition under

c;,:-:litions zhicli I,".1.- that either the absolute 'nop-, 7.r of reinfo J .'.

or non-reinforcod. responses each S emitted on each .ip. '.; duri

each expcrJ.-.:r-t:.l session wore equated. Acquisition performLance was

not diffe.:: .t.1 affecte.l by th three le,.io-L, nor by equated

reinforcA-.l or non-reinforced r:.;c:-in>. Reversal performance did not

differ for the n0ozortically and hisp.-:_-.:-' lly lezio:.:d Ss, but both

app:-c' to be facilitated i,'-- compared to sl.'uJ control Ss. As in

acquisition, equated reinfoicel or non-reinforced responding did not

differentially affect performance of the three lesion groups.












The hip_ ,- _-:pus, nestled in the ir-erl folds of the temporal

lobe, has been subjected to more intense experimental investigation

within the past deri.e than in all previous years combined (after

Douglas, 1967). The early neuroanatonical investigations of Papez

(1937) which first linked the paleocortical structures of the rhinen-
cephalon with emotional behavior were z:..:rted by the contemporary

experir.i-cnt.l investigations, perfor7,- by Kluver and Bucy (1939), of

the effects of tc;- :.:1 lobestec-.j on beha-ior. MacLean (1954, 1955,

1957, 1958) fcx Jised this orientation, postulating a dichotomy bet'.-ee
the phylog:-.n:ticcally older p leocortex and the more recent neocortex.

The former was p s:er;ted as involved in variety of emotional and

visceral f; .cions, while the latter was t.c... t to be-coicarnd with

more cognitive functions. However, as the hippocaarpus was subjected

to more intense experiimental investigation a more cop-lex picture of

hippoc-:?--l function emerged. Before suinarizing the results of more

recent investigations of the role of the hippoc.- pus in behavior and,

concurrently, reviewing the physiological theories of hippocanpal

function which habe emerged from those data, a general description of the

hippocampus and its' interconnections with other brain structures will

be provided.

The hippoc--Apal formation, composed of the hippocampus (Ammon's

horn), the hippocampal gyrus, the fascia dentata and the fornix,lies along

the medial and ventral border of the temporal lobe where it is wrapped


IN:rOLUCTIO'N










around the posterior surface of the th!a':1us. T-- hippocerspus,

re-ininrcent of the common sea horse .o_ c ous. hitoooca: ous from which

its name is derived, is the -ajor structural component of the hippoca-.:pal

formation. Gross description of the hippoc~apus was provided by lorente

de No (1934, cite! in 1o1ilack, 1967) xho divided it into four s-egJnts:

CA1, located pr:-: 1 l to the subicuilun, Ck2, CA3, and CA4, lying in the

fold of the gra'~-le cell layer of the fascia dentata. The most generally

accepted cytoarchitectonic description of the c.-plex internal structure

of the hipn.c-p--us was provided by Cajal (1955). Starting front the

ventral surface atove CA2, thenprocedi-D vertically, seven Zajor

layers are evident: the ventricular epen,,_ -_, alves, stratau orie-ns,

stratu rial strataui radiun, stratum lacunosu.-, and stratum

molecular. A detailed exposition of the int. al norpholos/ of the

hippocampus and hippc.- .-.1l formation is provided by Meissner (1966).

Two major afferent p-th :-ys serve the hippocampus: the alvear

path through the fornix system and the perforant path through the subicu-

luem. The fibers of the fornix arise primarily in the septal area and

the intral-nir.t.r nuclei of the thalanius (Gr';:n & Adey, 1956). The

system is more involved than this, however, for inputs also reach the

hippocampus from the asc-endin-r reticular activating system of the mid-

brain and th2la-us (Sermn & Arduini, 1954) and from the hypothal. lnus as

well (Feldman, 1962). The perforant path reaches the hippoc:::pus by way

of the entorhinal cortex and sublculu'-. The temporoamonic tracts pass

from the entorhinal cortex through the subiculum to the hippocampus

proper. The entorhinal cortex, in turn, receives its afferents from

considerable areas of the neocortex (Green, 1964). In addition, there is








evidence for direct fibers from the cingulum attaining the hippoci-pus

via the perforant rath'ay (Adey, 1961).

Fibers passing into the fimbria constitute the main efferent

pathway of the hippoca..-pus. These fibers cross to the contralateral

hippoc-:.i'Js via the hiv..caepal commissure, or enter the fornix and

project variously to the septum, hypothalanus, anterior thalamus, and

rostral portions of the brain stem (Green & Adey, 1956). The hippo-

campus also gives rise to efferent fibers to the entorhinal area via

the temporoanonic pathway. In addition, Gloor (1960) presents evidence

for primary hippoc ::2'"-'.gdaloid fibers as well as secondary &.:10.lo-

hippoc':--- connections. An int-7-ive review of the literature pertain-

ing to the neurco%-to:.ic.l investigation of the hippocampal afferent and

efferent systems may be found in Gr.;n (1964) and Str::f (1965).

In an attempt to assess the contribution of the hippocampus to

the physiolLgic21 substrata of behavior, researchers have examined the

effect of hippoc- pectomy upon a wide variety of behaviors. One of the

most studied classes of behavior falls under the general notation of

avoidance conditioning. Interest was spared in this paradigm by the

relatively early study of Kimura (1958) who found that rats with bilateral

posterior hippoceapal lesions were deficient when compared to neo-

cortically lesioned and sham operated subjects (Ss) in their ability to

vithold a well-practiced, food motivated approach response following the

introduction of punishment (electric shock) of the consumatory response.

The essential characteristics of this experimental paradigm are proto-

typic of what is generally referred to as passive avoidance conditioning.

Such deficits in passive avoidance have since been replicated under









varyih- conditions in nMuwrous studies (e.g. ICscon :;:ic~.:1- l,

1962; Ki:ble, 1963; cite]L:-l & !:il r, 19?3). Those styles which

have failed to replicate thcso findir s have reported restricted. lesions

involving only the dora1 portion of the hippoca-.s (3oit':.o & I cs. or,

1966; Kvcin, Sotcklicv & KaYv, 1964), or have employed a response of

low probability (Ki:.ble, Kirkby & Stein, 1966; 'i ocuir & jills, 1969).

It is possible to ccistract various cxplc.tions of the i cderlyinr;

nature of the. o- .hippoc- pcto yi deficit; o'ne such s.. ;estioa

is that hippos., l lesions in so.e wvy vitiate the aversive effect of

the p nishiig st.ili s. Such a position woui 1. lead to the prediction

that hippoccI- actoeiz cd S vould 12 deficicit in a vide rP of sheI

moti e1 tb:; :'.-ir This cdoes not arp to b the case, ho- er, for

.,hip .3cto:id Ss are not nc. C ;: rily roI rd .' :1ei coi .rei to

control Ss in their ability to a"ter a variety of active avoid.ace

tasks.

In the typical one-:ay active avoidance par-ad.ii Ss is required

to zIOve front c-.-. conpart-irent of a shuttlebox to a second in the presence

of a warning signal to avoid an avcrsive stimulus is delivered and S mist

then perform the response in order to escape from it. Follovitlr completion

of the trial S is returned to the original compart.,nt of the shuttle-

box and the procedure repeated. Although Niki (1962) reported that

destruction of the hippocatpus had no effect on this variation of

avoidance conditioning, more recent investigatiL:z have indict--t that

there is a lesion-i:2.ced deficit which, h: ::'.cr, appears to be of a

lesser relative ?-ritude than that found in the passive avoidance

paradigm (':::"-' & .." son, 1966; Olton & Isaacson, 1967).









If the above avoidance paradigm is modified so that S is not

returned to the original compartment of the shuttlebox following each

trial but inste-'f must return to it as the response in the following

avoidance trial t."e task is reter.-.A t-:o-.':y active avoid.:e. .:hen

compared to neocortically lesioned and sham opi'rat>.d Ss, hippocanpectom-

ized Ss appear to be facilitated in the acquisition of this iespons

(Isaacson, Dou.-.s & Moore, 1961). It has been sj;:3ted that facili-

tation is due to the p.-ese.ice of a passive avoidance component involved

in the t'o-: 2 active avoidance paradigm which interferes with acquisi-

tion in control Ss (S is required to return to the compartment which has

most recently betn associated with aversive stimulation). Hipoc:-.,.:-

tomized Ss which have been demonstrated to be relatively ip-rvious to

the effect of the contingencies necessary for the instate-ent of the

passive avoidance response are not so hampered r.d consequently acquire

the two-way active avoidance response more readily (T-:la-s, 1967). The

slight deficit seen in th- hippocampectomized Ss' acquisition of the one-

way active avoidance task can also be related to the deficit hippo-

campectomized Ss manifest in passive avoidance. Here, however, the

hippocampectomized Ss' tendency not to avoid the compartment associated

with aversive stimulation retards acquisition relative to control Ss

(Olton & Isaacson, 1967).

A second formulation of the underlying nature of the hippocampal

contribution to behavior which, like the aversive stimulus position,

relates to the passive avoidance deficit suggests that hippocampal

lesions enhance the reinforcing properties of appetitive stimuli or,









altei.-:tively, holds that the hipo ac:.>l lesion in so:e fashion eleDates

drive level relative to non-hippocSsupectodized Ss under equal levels of

deprivation. J:-. .rd (193) has briefly reviewed the lite-ture which

supports this position and points out that in a:lition to the intimate

conr-ctions of the hippoc- ,; ,ith structures important for physiological

ho.eostasis, behavioral evide..:a indicates that hi;.*-."e. -ctonized Ss

are more active in both novel and non-novel situations, ini-ease their

response rate for food and water, atid show sloc. extinction of a food-

motivated running response. Altho-ugh hip:oc=ap-ctoMzcd Ss have not

been^ found to eat more food then control Ss, they have been found to

drink more after It has b a-r ed thl-t the increased drive

hypothesis zs hasz ,.:r-7 been abtE. oned o (: .jlas, 197). However, the

ar---.J-.:its marshalled against this position have stressed the findings

of the avoidance conditio..i,' ;-:-_l:.. and reasoned that because

hippoc:.:':tr.-e. Ss do not appear to be more sensitive to the drive-

inducing properties of aversive stimuli than do intact Ss, it is

inappropriate to posit that the reinforcing. or drive reducing prcp-erties

of appetitive stinuli might differe-.tially affect h .poc.-.-:'pectomized al.v

norLal Ss. Such a critique is cogent orly if the theorist holds that

a unitary or one-process theory of hippocampal function will explain the

whole spectrun of lesion-induced behavioral ar.:, ..ies. Whether it is

possible to formulate a one-process theory of hippoca2pl function has

yet to be demonstrated.

The deficit seen in the passive avoidance performance of hippo-

campectomized Ss has also been viewed as a manifestation of a general

tendency towards response p:r..coveration or, alterr:-tively, an inability

to inhibit responses. A considerable body of evidence is available in

support of such a position. Correll (1957) foun-d that cats subjected







to bilateral hi,:. -'-.1 sti:.ola.tion during the acquisition and ex-
tinction of a food-moti,.atel straIsht alleyway running response sh:e-l

no differcace in rate or acquisition :*.:- compared to control Ss but

did require a greater number of trials in extinction. This firing has

been reliably rc-lic.%ted in rats following hih-.n:J1 destruction

(Jarrard & Isaacson, 1965, Rapholson, Is:.:c3:n & Douglas, 1966). A

closer e~:-irnation of the phenomenon indicates that the interval

between extinction trials is an important variable to be consid:1rl,

for while the incre-;:i1 r:-sistance to extinction is deLonstrable when

trials are sp-ced, the h1p;..'capal lesion deficit dliw:ppears in the

massed presentation of the extf..ction trials (J:- ?,rd & Is:aacson, 1965;

Jarrard, Isaacson & Uic'" l'.cn, 1964). Both Peretz (1965) and c .L.i..l

and Pribran (1966) have reported that hipn. :."pectomized Ss show shorter

response latencies and a greater number of responses to extinction than

do control Ss. Increased resistance to extinction has also been dem:on-

strated in the t'o-'.a active avoidance paradigm (Isaacson, Douglas &

Moore, 1961).

However, Schaltz and Isa_-con (1967) h-7e presented slightly
divergent findings concerning the perfcrLance of hippoc:npectoOized Ss

in extinction. They ran hippocampally lesioned and control Ss to complete

extinction in as many 30-minute free operant sessions as were required

for the attainment of their stringent criterion. No difference was found

between the experimental and control Ss in the total number of sessions

required for extinction. In addition, the hippocTmpectonized Ss shoved

shorter response latencies in only the first extinction session; no

differences bztw'-?n groups were four.1 for any of the subsequent sessions.









Kal.ni (1967) has reported that hippocvazp3cto:;ized Ss sho'r faster

extinction of a freezing reaction t..:':-, as ;'. .:tive of a classically

conditic .:1 emotional response.

The general inability of hippoc .; lly lesioned Ss to inhibit

responses has becn widely demonstration in a number of other situations.

Ellen anrd ilson (1963) found hipnocaipeactonized rats impaired in their

ability to inhibit one type of bar press o-. alopt a second follc'.:i:. a

change in the response requirements for reinforcen nt. Both .iki

(1965) and S,anson and. Isa2cson (1967) have de. -..st \,i a hippoca-pal

lesion-iniduce. deficl-.:,- ; in yielding to stir-lus control following

the initiation of SD-S6 training. Ho' .x:r, the latter authors also

dcnonstratel that hip-Scspctoiz d could readily acquire the

discrimination provided' they were not subjected to a lorg pst history

of continuous reinforc-::nt for r... 'I..n.j prior to the initiation of

discrimination training. Clark and. Is" -.;:... (1965) found that hippo-

campecto.ized Ss were less efficient than control Ss on DUL s:-;illes

of reinfo:cPe'--_nt. A follow-up study by Schialtz and Isaacson (1966)

presented findings analogous to those of C1: a-d Is-,:son (1965),

indicating th-t hippocampally lesioned Ss could perform well on DRL

schedules if not first subjected to prolonged crf training.

The apparently critical role of past learnn.r. in the demonstra-

tion of hippoc.:...pl lesion-induced deficits in discririnartlon and DRL

performance su listedd to some that the hippocampus was not involved in

the inhibition of b.?hr;ior in general, but was more specifically necessary

for the inhibition of well practiced rcsp'nses. The demonstrations by

Kimble, Kirkby and Stein (1966) and W'inocur a!.' Mills (1969) that






hippoc- :-ctomized Ss showed ito deficit in their ability to inhibit an

unlearned e.r-..i response fro- a snail, elevated perch when the response

was punished lead to their for:l! statement of that position. However,

Isaacson, Olton, Bauer and Swart (1966) and Teitelbau: and Milner (1963)

have presented cc-.tradictory data, inlicatirg that hippoca pectonized

Ss are deficient in withholding a naturally occurring response involving

a step-C-& !L from a platform to an electrified grid. The former authors,

who shook the platfoi to increase the probability of response oc..c..nce,

s1i.-ested that tV- escape response employed by Kile, Kirkby arnd Stein

(1966) was too weak or inprobable in nature to adequately reveal a

hiIp:,,capal lesion-indnuccd deficit.

Inhibitory deficits of bippSSoc.:pcto::izcd Ss hae also been

widely exa2ined wit.;;: the context of exploration and s::.:itaieous

alternation paz-rL :s. Roberts, Deuber a:d Broduick (1962) c.o-:' cd

exploration rates of hirzocanpecto)ized and control Ss in T- a-.- Y-Mazes

and fo.._1 no differences in initial rates, but a more rapid decrease in

exploration rate in control than in lesioned Ss. An additional analysis

revealed that Ss with small hippoca!ipal lesions showed a moderately, but

significant, slo,..er exploration rate decrease than controls, and that Ss

with "iLsive hlppoc...;p:l destruction showed no rate decrease whats.osvcr.

Leaton (1965) studied opportunity for exploration as a reinforcer of a

T-maze turning response and found evird:,e.o for acquisition in normal and

sham operated Ss while hippocanpectomized Ss were unable to overcome

perscver-ative teidencies and cons-.u; tly show.ied no acquisition effect.

Forced training was instituted in the second phase of the experiment and

.o.'-ui. of running speed .;cre ta cn. I'.e hippocai:poctomized Ss showed

slower habituation to the reinforcer, i :..: by a slower decline in









runiig3 speed over trials than control Ss. Kirkby, Stein, Kiftle and

Kiible (1967) examined perseveration of a T-7aze response as a function

of gojl-box confinement. With short confinement periods (50 seconds)

hippocaspsl lesioned Ss showed perseverative L- vior vhil- control

Ss spontaneously alte.:-'2:. their responses on successive trials. With

longer c:.fiae:::,.t periods (10 e 50 rcin-.es) both hippoca pectonized

and control Ss den.onstrateJd s:; t'.: :.s alteiration.. A supple. -:ntry

analysis rv"aled hippocatpectoaize3 Ss'perseverate responses Der se

rather than responses to s52ified locations.

Studies of the effect of hippoc- -.l-' lesions upon caze learning

have yieldeol rather consistent res-ults. In ::-"ral, the hippoc.2pap

lesion-induced deficit is sl .:t, if present at all, in very simple

mazes, but as maze complexity increases the lesion-induced deficit in

acquisition becomes incr-:s:l:7 :--r:.' rEanifest. These fi. r.ls have

be-en attributed to the hippocantpectomized Ss' inability to inhibit the

reentry of previously explored blinds and the g-ter fre&-:r.cy of

blinds in p:o-,r:sively more complex cazes (Kaada, Pasnussen & Kviea, 1961;

Kimble, 1963; Kimble & Kimble, 1965). Hosteller and Ih-.:is (1967) have

demonstrated that the hippocampal deficits in maze learning cannot be

attributed to enh:ncel thigmotaxis. The hippoc-:pal lesion-induced

changes in spontaneous alternation and maze performance suggested to

Kimble and his co-workers (Kimble, Kir'rby & Stein, 1966; Kirkby, Stein, Kimble

& Kimble, 1967) that hipp.-ca.-jpectomized Ss suffer from a reduced rate

of information acquisition. This position is inco.:plete, however, for it

fails to account for the unic-ired acquisition rates hippocaapectomized

Ss demonstrate in alternative learning p.rad5.,s.








Although h-ix:, jectoaized Ss appear deficient in their ability

to withhold rs.ons ,s in successive or go-no go discrimination problenis

(Kimble, 1963), numerous cz-1..is have demonstrated that theydo not

differ from control Ss on a vide ~-,-iety of simultaneous discriL.-i:rAtion
problems (Alleyu, 15'..:, 1941; Bro.n, Kaufnan & :-rco, 1969; Grastyan &

Karmos, 1962; Hir:nr,, 1966; Kimble, 1963; i'Nble & Zack, 1967; Swann,

1934, 1935; Teitell.-.., 1964; Webster & Voneida, 1964). *;h-n, hippo-

campectonized Ss are requiral to reverse sic a discrimination, a

pronounced deficit in shifting responding froi that which was previously

reinforced to that which is ne.ly reinforced is regularly observed

(Bro.:.:, ?.-.: _. & Marco, 19;2; Kiqbie & ..-'le, 1965; Rabe, 1963; Stutz

& Roc;:lin, 1968; S'anson & Isaacson, 1967; Teitelb h-a, 1964; T*'!-.-o.pon &

Langer, 1963).

In an attempt to explain the c.'-o. s observed in positively
reinforced b:h:nvior following hippoc-'.;ctoay in terns of the loss of a

single process contributing to such behavior in the intact organism,

Douglas and Pribram (1966) develope. a sophisticated neurophysiological

theory of "problem solving." Although the authors were initially con-

cerned with the hippacczpus, they found it necessary to include in their

theory a second limbic system structure, the anygdala, in order to account

for the behavior of which hippocampectomized Ss are capable. Each of

these structures is postulated to be intimately involved in two distinct

processes underlying problem solving or discrimination learning: the

hippocampus-centered "error-evaluate" process and the complementary

aeyg-di-l.-centerZs "reinforce-register" process. The terns are indicative

of the function of each: the reinforce-register process is depicted as









increasing the future probability of a response which has been folloJeal

by reinforcement; the error-ovaluate process is postulated as decreasing

the future probability of a r: ;nse which has not 1K-' followed by

reinforce&.ent. During discrimination learning in the intact organism

both these processes or systems are cooperative as behavior is brought

under stimulus c:,ntrol.

The propose. neuronal system undcrlyirg the error-evaluate

process involves hippoca.:pally mediated inhibition in a P -:.!.-like

mechanism within afferent systems which serves to "gate out" non-

reinforced stimuli. In the absence of the hippocampus non-reinforcL-:nt

cannot alter bh ior ard discrimination learning cust be accomplished

by the remaining reinforce-register system The effect of reinforce-

ment termed "iipellence" is i:-::- -'ta over reinfo._:! training,

constant in size, and related to the roagnitude of reinforcement and the

effort required for its production. At the primary neuronal level,

impellence is depicted as involving normally occurring collateral

inhibitory processes in afferent systems. The work of De.:'son, Nobel

and Pribra,. (1966) and Spinelli and Pribram (1966) is ta-en as direct

evidence for the exist-nce of these proposed systems.

To sumirarize the Douglas-Pribram theory: It has been suggested

that the hippoc.-.pus is a key structure in an error evaluating system

which mediates the effect of non-reinforced responses during learning.

Organisms with hippocampal disruption are rendered relatively in-

sensitive to the effects of non-reinforcer.czt a.d are therefore required

to learn appetitively motivated tasks via the remaining reinforceuint







sensitive amygdaloid system. Although t::o theory is a posteriori

in construction, Douglas and Pribram (1966) do present soie data

confirming predictions made from the theory.

The present experiment focuses upon the hippocampus and its

proposed involv;::wit in situations involving non-reinforced respon ir .

An experimental paradig3 in which manipulation of reinforccen:, and

non-reinrfoi'c-.t contingencies gr.cvctes differential predictions

concerning the behavior of hippoccapectomized rats has been developed

from the theory in question. In both the acquisition and reversal

phases of a position discrimination, equation of the absolute number

of reinforced res:--r.ses to each of two to-be-discri:-~..tci r:.ipu-r,.'-

ccbinrr2 with differentiation beaten the two in terms of the absolute

number of ncn-rei:.:'orced responses would be predicted from the theo'zy

to retard both acquisition and reversal in hiL:, ..-p-ctoaized Ss when

co-parcl to neocortically-lesioned and sham o;,rated controls. Ho-.:cver,

when the absolute number of Lor.-reinforcdl re;jonic: to the nr-mnule:Ja

are equated and the number of reinforcJ.l responses differ, any hippo-

cazpal lesion-ind-.-ed deficit would be predicted to be of a significantly

lesser magnitude if present at all. Positive results would constitute

support of the Douglas-Pribram theory (Douglas, personal communication,

1968).















Subjects

The Ss *'_--- 60 male Lo -' rats .pp-roxi;ately 125 to 175

days old at the start of training.


Awparatus

A total of four expert' ::tal chambers were employed. One was

constructed in the laboY "-.tory uhile the remaining three were coLsercially

obtained. The.c.atber :tactoed in thie laboratorY *a:s a converted ice

chest with a she.t.-ta1 partition dUi-.ldi it into two cc_:.rtients.

One coipartrenat co2ntained a pellet dis3nse~ r and relat-ed reinforce:_ent

delivery equ'. .-:'t; the second co-par- .At, with the inclusion of a

hardware cloth floor, ': -"r:i 28.5 :.'. by 28 :-... by 23 :-1. high and

served as the ex priLental space. A 7?lTh GerbranLds Co:-.:'!y rat lever

was situated along the verticle center linr. of ore wall, 2.25 ::.. above

the hardwarecloth floor. Reinforce> ::it was delivered to a food cup

situated 5 ms. above the Lanipr.l=.n.u. An e:I.-: st fan provided ventil-

ation, and a 20 VDC bulb located in the center of the ceiling provided

illumination during experimental sessions. The coanercially obtained

chambers were all Lehigh Valley Electronics Model 1316 small cubicles.

A metal food cup was located along the verticle center line of one

vall and rested on the grid floor. Two Lehigh Valley Electronics Model

1352 rat levers were mounted on the same wall, one on each side of the

food cup. The center point of each ranipul--.' .: was 3 ic. above the







floor and 5 m from the neari7t side wall. Illumination was provided by
a 20 VDC bulb located 2 mn. above the center of the plexiglass ceiling.

All c --nipulanda were c--JLil:-ut so t'-.t a weight of approximately 20
grams would activate the r.;ponse circuitry. All e:;2ricental operations

and contirgencies were controlled by a 't..:- tic elcctro-nechanical

programming equipment. Reinforcement consisted of 45 ag. Noyes rat

pellets. A plexiglass cover, measuring 3 :.=. by 7 mn. by 14.5 22. high,

was available to cover either -:.npul-:r.tu in the two manipulanda

chambers, thereby forcir.:- Ss to r3,rnri on the uncovered .I.. i-- T.--iA
when the condition: of trin rj so required.




The 60 Ss were assigned in equal :rn.'rs to the 6 cells pre-

scribed by the first two factors of a 3 x 2 x 2 experimental design

involving re-:zted measures as the third factor. Animals subjected to

hippoc~r:-.1, neocortical, or sham lesions (factor A) were assigned to

conditions of differentiation training which insured that for each daily

session either the number of reinforced responses or the number of non-

reinforced responses (factor B) emitted on each of two mnaipulanda were

equal, and were then tested in both the acquisition and reversal

(factor C) of a two manipulanda differentiation.

Procedure

Upon receipt from the supplier all Ss were placed on ad lib

food and water. Following recovery from the rigors of shipment a mean

base weight derived from five con:ccutive days weighing was established









for each S, and Ss were r :.' i to 8,' of these valr':. an maintained

at that level for the duration of pretraining.

The goal of the pretra in.L phase of the experiment was to

establish in each S a bar ;r;:3 response free of a~,y procedurally-

induced left or right position preference. To accol-..1ih this pre-

training was corKucted in the single anipulandi.u: chaToier. Subjects

were first magazine_ trai-ned and then z'. to pt'&z the manipulannd.a

by the delivery of food rl-...orcemsnt. Special care was t:h'-:- to

insure that no S received a disprcoiriLer-.te amount of training under

crf and low FR reinforcement schedules. Trh reinforcement ratio was

gr-.l.lly escalaPted and. preu.:-.-.v1 was terainatod pon each S's

de:oi.stration of stable respondin under the requireants of an FR 10

reinforcement schedule. Subjects were then returned to ad lib food

maintenance.

Following ric.overy of lost weight Ss as i :7:; to the appropriate

cells of the factorial desi-, were subjected to bilatteal hippoc:..I.:.l

removal, bilat.r.l removal of the neocortex overlyinr. the hippocampus,

or bilateral shank operations in which the dura overlying the neocortex

removed in the neocortical lesions was exposed. Follo'rin. recovery fr'o

surgery a mean base weight derived fro: five consecutive days weighing

was again established for each S, and Ss were reduceLe to 85; of these

values and maintained at that level for the duration of the experiment.

Subjects were then returned to the single manipulandun chamber

and retrained to respond under the conditions of the FR 10 reinforce:.:nt

schedule. With few exceptions reestablishment of control of responding

by the FR 10 sche.le was accomplished during one session of approximately









45 minute: duration. In no instance did this retrALT.ir, require more

than three daily sessions. Following completion of retraining in the

single ',.iril.-P..,, churTar Ss '.",- adva:.-c, to the two manipulanda

chambers in which the expert -:,tal operations were conducted.

During preli .ry trC in- ij in the two manipulanda chambers the

right L,:n.-_i2,-A-.2 .n was first c). i:- with the plexiglass cover provided

for forced traid.1j: Responding on the left r'anipl-.:.': was first

maintained by a crf schedule of reinforce-ient, a,-. then by intermittent

reinforcement. The reinforce -..t ratio was escLl'.'c 1 one step follow-

ing every tenth reinforcement u.'tll 10 reinforce-ents onan 7R 10 schedule

were delivered. Subjects were then removed froi the chibs-r, the plexi-

glass cover roved to the left manipuilandc-, and the preliminary training

regimen r:,:..ted. Those Ss which failed to earn 10 FR 10 reinforcements

on either -::,:.p-aiudum within a 5-minute period during which that

schedule was in effect repeated the preliminary training region the

following day. With few exceptions pretri-.1in._ required no more than

one session approximating one bour in duration; in no case were more than

4 daily sessions required. On the day following the co:.pletion of pre-

liminary training the expericental procedures were initiated.

In discrimination acquisition responses on one ranipulandur

were reinforced onan FR 5 schedule and responses on the second were

reinforced on an FR 9 schedule. Of the 10 Ss in each of the two hippo-

campal and sham lesion groups, 6 vere assigned to one chamber and 4 to

a second. Within each group the relationship between manipulandum and

reinforcemcalt schedule was. counter l. .anced. The two groups subjected

to neocortical destruction were assigned to the third chamber and the

relationship between manipulandum and reinforcement schedule also counter-

balanced. The first portion of each daily e:,:perimental session consisted










of a 5-minute free choice period drin which both manipulania were

ex,:" :e for re.- :-r.-.r. andr reinforced on the appropriate sc'.: es. At

the con: .uj-ion of the test period, which sered to monitor the formations

of the discrimination, the ntber of responses emitted ar. the -I'"sbr

of reinforceaeats L rns d on eacb Laniplai wer-a re .:"'ei. The-

forced training p',.tion to the epriental session .as then initiated.

The purpose of fo:c'2 ti 1. '- differed for each of the two

hippocapal, neocor-tical, and sha'2 lesion ,.ops. One each of the

hippocli.:pal, neocortical, and sham lesion groups Vias rtn under the

ccr..l'tion presc:bin the e:uation, for each S, of the absolute r.:::-

of reirforccl reo r.:s e tced or, e .: rr::2le : during ceCh

daily session. The second hippoca-.pally neocoruically, 2 sa

lesic .?. groups were run unicr the conditioning prescribir the'

equation, for _:'_ S, of the absolute 1: .br of no..-rinr.forced

responses emitted on each ianipi: n> .- d.'ing each daily session. It

should be noted t-.at as a result of the utilization of an !- 5 and an

FR 9 schedule of reinforcement, Ss :.':h emitted an equal number of

reinforced rcsponc.. on each r.:nijl-1,. also emitted twice as :rny

non-reinforced responses on the FR 9 ca.'..la..l.'u as on the FR 5

manipuland-m. Conversely, Ss which emitted an equal number of non-reinforced

responses on the two ,nip..lardi. also emitted twice as a=ny reinforced

responses on the FR 5 m-nipulanrtv as on the FR 9 nLnipula.'nr.

Subjects assigned to the reinforced responses equated procedure

fulfilled a dual relulre: nt during each complete experimental session.

These requirements were: (a) each S earn an equal nurbcr of reinforcements








on the 7. 5 and P2 9 m i:.-l.., a-d (b) a total of at least 50 rein-

forcements be earned on each of the two manip!l?,I-. If S did not

earn the minimum 50 reinforcements or either : :.i- i'..... during the

5-minute free choice period, the forced training portion of the

session involved r n fiJ.g. on both Lip -. alala. At th en d of the

free c-hoice period the required number of make-up reinforcements to be

earned on each r..: ni 'P-'-' was deteri'. 1, one anipul .:.. was

co-ve ed, and S was allowed to respond on the :::.. until the required

number of -':e.-up reinforcc::ats for that r-'.1 ulandun had been

deli,;-1v. The cover vwas then moved to the seco-d manipulanidu and

S was allowed to respod on the first until th2 require :ents for that

B:.';i..-.-' : had been falfille1. For ex::ple, if S ea:ned 40 F2 5

reinro'cennts and 25 Fa 9 rei-.rorce.ets du-ins the free cL..icc

period, S_ would be required to earnn a additional 10 PR 5 reinforce-

ments and 25 FR 9 reinforcements during the forced training period.

As a result, S would have earned an equal nr'.Lber of reinfo:rc':r:ts (50)

on each m aipula:.i during the course of the experi -r:tal session.

The order in which the manipula-.da were covered alternated across

daily sessions.

If S earned 50 or rLre reinforcements on either, or both

manipulanda during the free choice period, the forced training period

involved rzspo,,iirg only one r.niii'ulznda_. At the ter.iination of

the free choice period the difference between the number of reinforce-

ments earned on the two manipulanda was determined, and the manipulniduL

on which S_ had ea:..:. the greater rio'-:r of reinforcements was covered.

The S was then allowed to respond on the second raripLil-ndum until the









reureq ed n ... c' c.:..e-'.. re ifoc k sts deivered. For e: .ple,

if S_ earicd 65 FR 5 reinforcc.:nts ar.1 20 FR 9 reinforce;n2ts during

the free choice p-rioi, the :-" 5 mcanipulnda would bs c;. ered during

the forced trailiin priod and.' S would be alle.cd to rcspondl or- the l1

9 ranip, 1 -tl 45 reipforc,:i:.x ts htr ta been Ieli-vcr:.. This fu l-

filled thVe reqijirc:- nt that S e:it an equvi nmu:ber of reinforced

responses, in this instance 65, on each r.ipulan'2 during cech expcri-

mental session.

Subjects signedc to the L: inf'c:c: responscs equated

proc,-; ce fulfillei a different dual reful : ..t curing each experi-

mental session. 'Th7s r ce ir:Sc nts were: (a) each S cr'.n t:ice as

maniy reinforce-:2ts on th: FR 5 .ii.!-..l c s oc the 2R 9 2nipl -.

a-.l (b) a r.ini: i of 60 reirForc c:onts be carnl! on the 1 5 cTniz2 "-

and, consequently, a mini m'- of 30 reinforcements be earned on the

FR 9 manipulandun. -- free choice period, and subseqcnt forced tii.,-

ing proceeded in a manner analogous to that d.: ,clir t? above for the Ss

assigned to the reinforced responses equated relgien. In the percent

condition, if S failed to earn the minilau 60 0r.1 30 reinforcements on

both the F? 5 and :-' 9 n .ipulaada, respectively, durir.: the free choice

period, the force?, training perica would insure that these minima were

earnel. For exa-ple, if S earned 40 FR 5 reinforce..ents and 25 FR 9

reinforce:eants during the free choice period, he would be required to

earn an additional 20 FR 5 reinforc:-.:nts and 5 FR 9 reinforc::.A.its

during the forcEi training period. The S would have therefore er1rned

the c.ninru, 60 and 30 rein'orc.e-nts on the FR 5 and F: 9 ra'i;']2:?a-

durii:- the c.,urse cf the exoerinrntal session.







If S earned L:O:.2 than 60 ri,;..force:onts on the I-; 5 ranipuland~:1
and/or more than 30 reinforcements on the FR 9 man pulandum during the

free choice period, the forced, training period i'.A:ved only one r. '.,-

landun ..-d served to insure ti t the ratio of reinforcements earned of

the FR 5 r-Fnipulandti;i to those ea:nc on the FR 9 :,1-ifll.-..:' vas 2 to 1.

For e:,- i,1e, if S earned 70 FR 5 reinforcements and 40 PR 9 reinforce-
mt:-ts during the free choice period, S was recruire3d to ear an additional

10 FR 5 reinfo;c :e-nts during the forced training period. As a result,

S earned a total of 80 -i1 5 reinforceLsnts and 40 l. 9 reinforcements
dui-in the c'-..:. of the experimental session, and fulfilled the require-

ment that the ratio of :: 5 to Ji 9 reinforce:;3nts be 2 to 1. If S earnCed

90 :", 5 reinforcements and 10 FR 9 reinforcc:'ents during the free choice

period, S[ as require to earn an additior?.! 35 FR 9 reinfcAc.: .ts

during the forced tr,1,tuit,.' period. ThI S ther.7,ice earned a total of 90

FR 5 reinfo-,--:.,ts and 45 FR 9 reinforcE::ents, and the ratio of FR 5 to

FR 9 reinfoc.: -:-rts was again the required 2 to 1.

Discrimination training was terminated when S attained a
criterion of at least 90, rDc-.?i:ng on the -R 5 r-. i~ul r..- in 9 of 10

consecutive free choice periods. Upon completion of this require -lnt

S_ was subjected to one half esin as r-any daily sessions as were required

for attainment of the criterion and then n,'ed to the discrimination

reversal phase of the experiment. If it became statistically irpossible

for S[ to satisfy the criterion within 40 days of training Sq was con-

sidered to have failed to satisfy the requirements for discrimination

and was then moved to the discrimination reves.:-l phase of the study.










Discriimntiont re-iersal training ;'as instituted for cach S

on the day following termination of the acquisition portion of the

experir.ent In rer-?21 training the roA tion chip I.'. '*e reinforce-

menit sch1'nule a 3anip-~!..'. was rIseerse for each S. Training

in reversal proceeded in tie s" e fashion for the trio groups as

described in the aequisition p -se above. Reversal training was

teKrinated "- each S cat either the criterion of acquisition or

failure ~ est:.b11".: for the acquisition ph.mse of the stidy.


Sur er:y

All Ss -- re op-re:-'1 under :0 /1i,: Ilc:itPl astheei

su.-,.ete ted with .30 cc. of atropine injected int cton: All

opra.t.. p V- prforl: while S was held in a -ti -re stereotaxic

instris-,-nt. A dissecting sccpe was e-rployed to assist in the vi:i,1

0.I, _i of neocorcical ansd hi-.-:,c: .al removal. In all operations the

skull was exposed by Erans of a midline incision, bilateral trephine

holes were placed lateral to the r:i.dl.;' and posterior to bregna. The

holes were e:-L :*_ with rougures to expose the neocortex o;erlying

the dorsal and lateral portions of the hipp;:c..'.:.us. In the sham operated

Ss surg-.ry was terminated at this point. For those Ss sustaining neo-

cortical rc'-oval the dural was cut and the neocortex overlying the hippo-

campus was aspiratel off, with care te':ea not to damage the hi.ppoc:r-:.'s.

For those Ss subjected to hippoc-:L:pctony the operation proceeded until

the th-la-.us was exposed. In addition, hippocan-pal removal was e-;peni.3.

anteriorally as far as the hippc--.pal couissvure as vell as c:.:te:.ld

around the posterio-lateral surface of the thlanVus. Care was taken not







to : a Ie the t'ausis. Followi-j co!pl etion of surgery Ss were

ret .' to their hose cages and maintained on a water amd tetracycline

solution for there to five days.


Histo 1 7

Follol.0 the ter.. i-tic of the e.. .- iEent all Ss were sacri-

ficea with a lethl.1 dose of :eatbutal aresthesia -- intracardially

perfused with saline follow ezd by a 10C for1.7lin solution. All brains

wer.- then i,_., froi the brain c-.ities and those of the Ss in the

nec-.rtical anirl hippoc--. 1.. -1., were infiltrated with, a C.Id embedded

in, celloiin &ai1 sectioned at 15 u. .:c; tenth section was retained,

moutcd on a sl'i and stailnd with thio.in. In addition, for 5 Ss

in each legion --oup t'.:: section follo:'irg the thionin section was

stained with wile r". then mounted.











R SUJI .S


Tr'i.' s of represen-tativ cross sections through the hip, po-.

campal and neocortical le:i :- are presLented in Fi .i:-: 1 a7nd 2,

r-. :: tivaly. Eizpoaapal destracticn reSalarly involved at least 75;,

of that struactu.e and in all instance resulted in the complete

separation of th3 dorsal a.! lateral aspects of the hippoca' al foro-

ation. Spciic da::a to the tha1 .-as was Dninial aindi, when evizi-it,

was typically unilat- .1 it, nature. .. neocortical lesions did not

en...:- a vol 7e of tissue cora-.ale to t -' rc:oe,1 inr the hippo-

c.;:- lesi.cs bc.it d.id apr'- y ...t the nrocortical ,e.' .- tion incurred

by the hippoc2.-;ctcies. .:pc<-?al d: .:g resulting fro the neo-

cortlc.! lesions ,-,as minir-:1 if pr .-:.t, usually unilateral in

nat.It-. CGrozS e.x-zirnatioa of the intact brains of those Ss subjected

to sham, oporat:".:- r.-:--ei no discernible neocortical da:.age.

The sc-ii:s requiral to attain criterion in acquisition and

reversal by these shaa, neoe. :,tically, and hippocamipally lesioned Ss

trained under the reinforced responses equated re-:;- are presented in

Table 1. The trials to criterion for Ss assigned to the non-reinforced

responses equated cor.lition are presented in Table 2. Irspectinn of these

tables suggests there is an inverse relatic.:.-c'ip between perfoi_:-nce in

acquisition and rz7cr:al. It appears that Ss who readily attain criterion

in acquisition are retarded in reversal and, to a lezc:r de:'ec, Ss

who are retardc. in acquisition rpp^:r to perform well in rc.'er.-. To

test th: possil.lity of sucL an inverse relatic,.. .'ip, all Ss were ranked



























j j-

-/ i .


Fig. 1.-Tracings of representative cross sections through the
hiproc~ ':i lesion (After Pellegrino and. C;-:-- -., 1967).
















1 1 .


'N



0~


7
7


J,'


(I j~


Fig. 2.-Tr,-ciPs of representative cross sections through the
neocortical lesion (After Pellejrino and C-usan, 197).








TABLE 1

TRIALS TO CIT'i' '1.0I IN ACQUISITION AID PDSTESA'U FOR SHAM, lNI'OCORTICALLY,
ANID HIPPOCA71AILLY J :1 O 0 Sz !SSI.,.- -. TO THE REItO1.C. )
R --C' -; UJAlTi!) CODITiOI


Acquisition


Sham Co-.trol


Neocortical Lesion










Hippocri rl Lesion











TRIALS TO CzPRIT 100iO -i ACYUISITIC.: AD R -L 5OR SI.I, KC CORIICoLY,
AID 1. ". TY IO ) S ASSIG~ TO T:` -
P-' i. :A2C) P O:3S 1.JATE) CO D>TIOl


Acquisition


Rverzsal


ShamI C-. -.t


Hippocr #p1 Lesion.


Neocortic-al lesicn








from low to high on the nr.,' :.- of sessions to attain criterion in

acquisition, and front high to low on the I.Ln-? of sessions required

to attain criterion in reversal. A Spearrcan rank order correlation

coefficient (rs) was then co.puted (Siegel, 1956), and found to be

significant (rs = .47, t = 4.056?, df = 59, p <.001). Spearman rank

ornf2cx correlation coefficients were also comiputed in the sa.;e r,:.-lrer

for the shza, neocortical, and hippoca: pal lesion groups (see Table 3),

and for the three lesion :..'p; when further divided on the basis of the

reinforul% ve;-', non-reinforced r-..p-r... e.-u-ted dimension (see

Table 4). The former analysis indicates the inverse relatic,.:hip between

poifor:_:nce in acquisition and reversal. is present in only the shY.j

control Ss; the latter analysis r--:.1. that uhile the shan control Ss

unl;.r the rn:.,-reilnorced re: ,::: equated condition do sho! this

relationsh'-,p, their c':. terparts under the reinforced reson.%s equated

condition do not. In addition, the finer grain a.-al.ysis indicates that

the hipp:.-:- ctc.:Iz .1 Ss under;" the reinforced responses equated con-

dition also manifest this relatic.'ship, albeit to a lesser degree.

The sessions required to attain criterion in acquisition and

reversal for sham, neocortically, and hippocampally lesioned Ss under

the reinforced responses equated requirement are presented graphically

in Figures 3 ar.i 4, respectively. Analoges data for Ss under the

non-reinforced re:.ponses equated condition are presented in Figures 5 and

6. An analysis of variance assessing the effects of the three lesion

conditions, the two re-.rponse-reinforccct contingencies, and acquisition

and reversal upon performance as ii..c::i by the trials to criterion

measure was perfor.-c-1 (Winer, 1962). Since the trials to criterion









TU3LE 3

SP?.'7..: R I 0.i CO TiATIOI CO.L iICI.iS (r.) : SIAI,
NEPKCC..iCCL, 1D :IlPPO'CTA L vCI-0 G 3 .


Shmn Control


r = .51

p<.05
rs = .10


Neocortical Lesic:i


p>.05


Eippocac-pal l] sion


rs = .36

p >.05


*See text force i---i:i" pr.o. u2s.








TABLE 4

SPi2J.UA R%':: ORDIl CO.- .L. 'O.i CO-, ,-ICi .. (rn) FOR S LAM, NEOCO.iIC.'L,
AND HIPPOC C'PAL I-:I C:.'":"; U..-. .,'-' : ORGE2),
OR 1 "- : ".. O ".D R .BDINC- DU-N I .D:. ',


Reinforced IRc. ,,..,-s
Equated


Oi-Rji fzorceIl Responses
E uated.


Sham Control



Neocortical Lesion



Hip :,.:- 1 Lesion


*See text for ranging procedure.


p> .05


rs = .06

p> .05

r = .68
S
p<.05


rs = .76

p <.01

r = .29

p> .05

rs = .35


p>.05


rs = .12




















































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me2.sura pr ouced- slightly s'-i.-d d. t:a, thse vJlucs 1 %:I-, subjected to a

square-root tr" n-.ora.tion a a second analysis of variance perfor:cd

upon the resultant data. The results of thcse, t:wo analyses are presented.

in su':y fashion, in Tables 5 a.Ld 6, r ctivly. A comparison of the

two tables roce.l little inconsist ..y in the r .'.?ts of th> tVo



An e C.:'..tion of Fi:-. 7, which depicts the c:u.ulative per-

centafe of Ss in each lesion group attainIr: criterion in successive

five session blocks, su-;::ts that the neocorti-.1. c.-.3 hippocarpally

lesior. SS are sli'gttly facilitated ,ith r.e_ :-t to the s'- control

Ss in discVi'_inatico prfo:: Lco. The an lyse' of variance indicate

that this difference is not lare e.c'-; to 1' statistically reliable.

However, the rEsnIlts of the a.alyses do reve l a sitaificant int tion

between this factor and the acquisition and reversal phases of tr:'rir.

which -aust be e...:-.-.-:; b:ore it can be concluded that the various lesion

cor.itions have no effect on discrimination learniri.

A co>rison of thb effects of equating either reinforced or non-

reinfo;'c-l r:or.:zes during discrimination training is depicted in

Figure 8. Neither le-.l of this factor, nor this factor's interaction

with the lesion dimension, w,.. indicated by the analyses of variance as

differentially affecting performance in the discrimination task.

Inspection of Figure 9, which reprLZEnts perform-ance in the

acquisition c.i reversal phases of the study, su. -c:ts that Ss attained

criterion more rapidly in acquisition training than in reversal training,

and this is verified as a si.,'Lficant diffc :'-:.e by the analyses of

variance.







Ti 5

ANALYSIS OF VONi.:CE 01 1:1,.JLS TO CRIi -,0ON



So1 CI-'-: MS df F

Between Ss 59
Lesions (A) 117.11 2 2.23
Response-Reinf,:.: .:t Ccnti: : c; (3) 151.89 1 2.90

A x B 2.79 2 0.05

Ss Within Groups (Error) 52.46 54

Within Ss 60
Acquisition.o-..- -:- T (C) 795.69 1 7.93:'
A x C 417.62 2 4.16*
B x C 1.86 1 0.02
A x B x C 83.21 2 0.83

C x Ss Within Groups ( 0-1rz) 100.35 54

*p<.05
** <.01









TATL7 6

ANALYSIS O0 VMARIIANC3 0 S 0 A5 T TRU S OE 0TION O TIAITS TO CRIT-RTC



Source YS df F

Between Ss 59

Lesions (A) 1.23 2 1.7

Respaonse-Rlifor c:ent Con~tinrscy (T) 1.33 1 1.91

A x B 0.02 2 0.03

Ss With Groups ( ror) 0.72 54

Within SZ 60

Acquisitio n.-.;ra., 1 (C) 10.96 1 6.61-

A x C 5.42 2 3.27-

B x C 2.01 1 1.21

A x B x C 0.04 2 0.02

C x Ss within G--.,: (Zrror) 1.66 54

*p<.05
























F' 0 )

o o 0

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1...y~. ~-'- 9 I I C
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co r- &to IA ;* c13 C" -


N01iJ 1i11 ON iI '1 I V.uV S 31rtsi f

:10 a0VIN3_2iEXd 3ALViflWO


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As indicatc.- .;-vl.icrsly, a sijni.c-it inter'ction bat:cc'. the.

lesions f,.tor j-.3 the A.-. .ition an: roeitsal phases of training vas

revealed by the c-. yses of variance. The co::poneuts of the inter-

action are depicted, in Fi-..- 10, hich pre:sets the prforaicc of

the three lesion groups in rquisition trnin, in Fgure 11,

which pre -..its their perfir -"c; in reversal tra-in'jnj. 1: ean triris

to criterion for Ss in each of the thrk~ lesicn groups is presented

for acquisition and r -:..1 in FiJure 12. F:-, r.-tion of those

fi-urcs su.s:ct- th-t the tL.',. lesion grou did not differ in the

acquisition pf:se of tr. .in, lut th-.t in thi revc-.1 pltase the

neocortic .y r ad hip po-t .ly Fic :.i.. S, -ils not clffuerin"e 2--

th-. "--2ves, did attain th criteric rc.. r.-:dil aid in geter narbrs

tl.:'" the sh.e c.:.:.L,.! .- -: co:S. AisC.s b tv:~ a the cell

means involve in this interaction vero I .:oric utilizin- the

Stulentizcd range statistic (,Uinr, 19(63) The results of the compari-

sons are pr. .cnted, in s u::,'ry fashion, in Table 7. The results s. -ct

the above observations and reveal, in addition, S'.,.t shan cont..l Ss

attained criterion significantly faster in acquisition th,-. in re:o.r:",

but that such a differ::!. is not prcs:,it in the neocortically and

hippoc: L11.y leio,.: Ss. Neither the r- :'L.,; first order inter-

action (lesions by response-reinforcement c.:tingency) nor the single

second order interaction (lesions by r.:.:'n.-reinforce-crt contin;.- y

by acquisition-reversal) attained significance.















































































t.> c co ca ca c~ ci c0 c. ca
C Q1 C C. C r- CL) LC3 C CN d (




ro tID> aAIJ)/irCMnJ


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STUJ -'TIZD ... S iSTIC A P03> O TI3S'


. tV..., .. . .


Shra vs. oecortic;.l Lesion

Sham vs. Hip c....plJ Lesion

Neocortical vs. Hippoc pal Ls.ion


Reverse .

Shi vs. Neoco rticc,. Lesion

Shra vs. ," ^c 1 Lesion



ShzR Cotrol

Acquisition vs. ?. -.1i


Neocortic:r. Lesicn

Acquisition vs. Revcrsal1

1* ;0


Acquisition vs. Reversal


3.09

0.86

0.83


20.29

13.'.

0.23


19.77r-


0.01


2.30










DISCUSSION


This study exauincd the p-irforiance of sham, ncocortically, and

hipp_:.c ll.y lesionea rats in t';.- acquisition an.1 reversal of a two

.manilj.:-. differ:-.tia.tion as affect,:... by certain L -,.,itic:. of

response-rrirnforc .ient contingencies. 7:: one-half the shaa, neo-

cortically, art. hip:.:.-. 1 :ly lesic:--. Ss, these manipulations insured.

that each S emitted n a jal l.;.-: of reinforced responses on the-

two .:ij.:i:.i duri--,: a complete expert. ..:.1 session. As a result

of this proc-:.:. e,ich S also c; itt.i t '- l: as .i, y non-reinforce

responses on one :-.:.li.u!,a:.: (th3 >: 9 r" ,.:lan) as on the second

(the FPR 5 r :u:.iladulm). For the re:-.inirj s, the experiknntal

m_;nipul.'.ti; insured that each S emitted an equal L.L:.:'r of non-

reinforced responses on. the t:wo r.:.:21.-L:. during a ceo.:lete experi-

ment..l session. As a r.-.it of this proc;l.,r, each S emitted twice as

many rei forcedc ri- .p.css on the FR 5 : 1-.:"..-'.: as on the FR 9

manipu~l:.."

The Doula.s-Prif:-i> theory of hippocampal fun.ction (Dc- ils &

Pribr-.n, 1966; D.ugl.s, 1967) is a vigorous attempt to integrate the

wide variety of beh-.vioral chng:s following hippoc:.-'..1 disruption,

and leads to clear-cut predictions of the bE-.vioral effects of the

manipulations performed in this stuiy. Specifically, the theory

predicts retarded acquisition and reversal in hippoc.:in-,l Ss when

compared to shai. and r-:cortical control Ss under the tre:.tment condition

which s pcifies e.'-ti.on of the ni-.i'ber of reinforced responses emitted

47









on th3 tw'o 01- 1. le n or no ro -,tic % in 2l -o. Ss

under th3 condition which s. -,. to equate the n'r2ar of no,-r1inforccd

responses emitted on the discrininanda, and, indirectly, no difference

bt'-:ee shan ard neocor'tical Ss uHiLrx either of those t;o. treat..nt

conditions. These predictions are contradicted by the re-suts of this

exnpsr-L .nt.

Tn:' trials to criterion Ld.t2:, do not reC7Tl ony differencEs

betweca the three lesion groups in acquisition perfor-. :e. This

finding is in g-ne. I1 accord with the r. .-ts of recent studies of the

role of the hippocampus in discriMin.tejon IoPai n. However, such

studies h7ve not e- ,.i:i ts :i 'fcc' c diffe.ti3 de1 cities of

reinforced and non-r iocel res3'.in to tVr clic e: tite disic i -

inanr.a upon discri.iJat.tioCi lsoini in hipca cto.i2ed Ss. The

r:.it fi''.., alt.' i-i inconsistcit with predicti.. deri..

the Doumlas-?Prith:: :'\el, i-licate that such differences have no sig-

nificant effect on acquisition perform: u'ce in either shaen, neocort'. :17,

and hippoca:pally lesioned Ss.

Thi performance of the three lesion groups in reversal also is

inconsistent with predictions derived froa the Douglas-Pribrai for,

as in acquisition, the two response-reinforcement contin,:ncies do not

differentially affect in either sham, neocortically, or hipt: :.:.W11Y

lesioned Ss. In addition, the reversal data appear to be inconsistent

with the bull- of the data on the perfor-.-ce of hippocampectomized ,.1

control Ss in discrimination reversal; namely the hitc.-.c.-lly lesione"

Ss are typically reported as retarded in discrimination reversal

when c..-. .lred to neocortically lesi(;..2 and shc: i control Ss who -: -.lly







do not differ eacich other. E :i results of tho present study indicate

that it is nec-:-ortically ae.: hip, .- .117 lesioned Ss who do not

differ fi.:. ech other, anl both : :-- facilitated when compared to

shm: operated Ss on the trials required to attain criterion in rv'::.-1.

A comparison cf the se-c.i-: to criterion data with alternative psr-

forance ness, su-ch as trials to successive criteria and the ab-

solute per ceot of :-' 5 reszi:: .-r for successive days, revealed that

all three c.. -: dpictc2' acquisition and r -:rsal performance in a

similar fash ica.

A p .:1. Mle epleanation of this da:-;:-ity is offered by the

relationship aciiticn aid re.--1 :.-Corc as revealed

by the Spear. r.. ': order correlation coef icicnt, i:- s. c opIrat t

Ss, w'-o r ,.i a signific:;tly .'-ter niI or of trials to attain

criterion in i T~r 2L. when c *-;. to the rc.cortically and hippo-

campally lesicr~d Ss as ir. ic?.ted by the St.'i-::tized r._:-s statistic,

are also the 3 who rianifest a s..iljicant inverse relatlo:..hip bet-ion

trials to cri'.. ,ion in acn,:-:ition and reversal. In addition, a greater

number of Ss in the sh:u.:i control pioui:, attained the criterion in 11 or

less sessions (15 of 20 Ss) than in either the neocortical (11 of 20

Ss) or hippoc: ;-.1 (12 of 2,' Ss) lesion 'c-r S. When the three lesion

groups are p-' L-tio:,'! in t-:..z of the response-reinforcement con-

tingencies, similar phcno-:ra are observed. These findings sug est

that scene Ss possess an initial position preference which, when in

accord with thec requirements of the initial differentiation, facilitates

acquisition ard retards reer:.'-. Moreover, it appears that a grcater

proportion of Ss in the shabi operated group fall into this category









tL-'. in ei'. "- of the t.:o cther cle ion goup. It : be e s;e:i, then,

that the poorer p or.nce of th sh:: control Ss in reversal is an arti-

fact resultirj fro.: a failv.: to co.- ...tely control for initial position

preference, anal that if this h-a b,-n done the differ.-ices bet'.ee the

three lesion groups in rcv.ersal ;:ul: be eli'irnatcl.

The expr 'i ental procolures e.ployc*. in this stv-U differ in a

nmb..ber of details fir:.: those i ' hippoo al lesio-,inTucac. dFeficits

in discri-1. 17 C:.. reversal ?are con obserc: It is possible that the

lack of a lesieo-i;iucc: deficit in the prcs-et st"' le r attribt'.ble

to one or .ore of these cdiffer.c.ces. One such uod.ific otion involves the

utiliza.ticn of an 1C rtri 3 (rain oscc,'in7 fiollvi ttr i:.rt o, Of ritesrio!

in acquisitic. I nvestiga tions of the ef c, _L i u on revr l. in

the T- zcz ivdic- to that Ss subjected to, on the aere "A at C s';t 1.3

(Macintosh, 1962) and 3 (Publos, 1956) ti aes as -- ovevtrainin trials

as Vwer rcquizrei to reach criterion in the acruisiti:. of a discri' nation

perform~ better in reversal than, Ss without oei ,... (the v.:. ti.

reversal effect). An ezanination of Reid's (1953) data indicates that when

overtraining involve: less trials than were required to attain criteria., the

overtraininS revel-.1 effect is not seen. It is difficult to c':;:.- re those

procedures and the present one, for different responses and p.oc':dr.s were

employed. However, sir,.- this study employed only one-half as .mny over-

training sessions as were required to attain the acquisition criterion it is

unlikely that the overtraining Icv:.. 1 effect was operative. L:-_pite this,

an examination of the o;crtrair:ing reversal ph:-.::-on does add to an under-

standirj of the results of this study.

Macintosh (1965) r,'Les that it is prL. w-o L.j justifiable to

regard reversal learning as consistir: of two parts: (a) extinction







of a tendency to select the f.oir r SD, ad (b) r:--.ition of a ten-acy

to select the Ls'- SD. Stage (a), extinction, is usually reCard.ed as

contln.'l. so long as S scores below' chance level, and stage (b),

acquisition, is typically depicted as co uencing as soon as S begins

to perform .,:.- chance level. It should be noted that implicit in

the formnilaticx- described by Nacintosh is the generally accepted

assumptiontha.t learning is a continuous, rather than discontJh.1:-us,

process. ."n-: ther this is indeed the case has not yet been completely

resolved. T-: :. .t discussion is c-:,-]rned primarily with the

effect of att:...tional f:ct'L upon discrimination reversal rather than

with the ude.l .in- nature of the learning p:'ocess.

It is oft$n repo: that' ortrainij of a run.:&:.y response

rejlts in reaa.c, resistance to extinction (>.-:- r, 1963). It is

logical to -:. .:, ther.-:ore, that this p-:.: -.. is what underlies

the oci. Li. ni r.::'.1 o effect; namely, overtraining facilitate
extinction of ::-.,-.:s to th3 for-.-r SD in the formulation descriL:i

by Macintosh. This is not the case, h..cver, for overtrain :- in the

discrimination 1aradigm regularly increases resistance to e::tinction

of respoi,.es to the fo:.er SD (Macintosh, 1962). As Macintosh (1965)

points out, overtraining facilitates reversal of a simultaneous dis-

crimination not ,2c,.u:e of, but in spite of its effect on extinction.

This finding would appear to negate an extension of the frustration

(Lawrence & Festinger, 1962) and generalization decrement (Kimble, 1961)

explanations of extinction to the overt'i-.1nij-g reversal effect and,

by implication, to reversal training in general.









IIacintosh (1965) reports that c: isCeLit evJ cea indicates

ov;c tli-1 facilitates reversal by shortening, runs of i:.-; ct

responses durirG the middle of the reversal. This su -ts that ovcr-

training 1i c.s Ss' tendencies to respond to irrelevant cues c.. '-

reversal. There are to possible explanations for this: Either over-

trainin3 effectively c -,cs Ss to "adapt out" cues along irrelevant

dirensiois; or overtraining allows a.ple opportu-ity for Ss to learn

to attend to the releva-nt cue dimension. IcI: tosh presents evidence

which indicates that it is the latter alternative whichh uaierlie the

overtrai.n :.. reversal effect, -- I points out a distinction bstvecn

research utilizir, visual asnd spatial cues. Stve.iss whicl have in-

volved a si ulta-,, us Iviiel di C xincinuation (bicht .es;, sjttern, etc.)

invariiably produce the o rtraininr revc-sal effect, .. 1e those

studies y:Kch c;-l.oy a spatial discr1:.i..tion (left turn versus irght

turn in ?.and Y-:azes, etc.) f~ -.F ently do not. A major reason for

this, Macintosh contends, is that the rat (the cou.only used e:pr'i-

mental organism) is primarily spatially oriented and, as a c-:.cLuence,

spatial cues :-.-:, a high priority ver, without ovrtrlirnfr,;. Since the

rat is already attending mainly to spatial or position cues, over-

training would not be expected to havc much effect on performance in

reverzl. Conversely, the lower the relevant cue dl?-.c.o' is on the

Ss attendingg hierarchy," the more valuable overtraining .:.'ld be ex-

pected to be in fji-ly establishing the relevant cues in a position of

dominance. The L-.nitude of the ovrtraining rever.::! effect should be

inversely related to the probability that S vill attend to the relevant

cue at the begin;i.- of discriirI.tion training, ern to the nr:..l.r of

irrelevant cues involved in the discri::r,:-.tiotn.







rI..- p:z,..- di uZion is carkedly similar to the r., -

Prlbi-ar c...-.: tualization -:: the role of the c .: al. in discrimination

luAnlr. ; n e'ly, the registration of the effects of reinforceennt or,

altr,.lively ti:- directi. of attention to the ,'..'. of the ts.Y.

(relevant cues) associated ith reinforce;:eit. HFoever, the above

formulation of the functic' of attentic: -.' factors in discrimination

learning does .0a t inco: :. '. a pI;. cc: lanalco to t,':..t attributed to

the hip' ::.: ; the gatinf ..L of sti-..ai associated with non-reinforce-

rent. It will be recalled that -.) alternative to the atteiitional

r.':icl ir. Icate. N.t the c,- 1.Lr .:1 ij rcversal effect caIm be attributti

to the op:ort~-yity for Ss to effectively 'a apt out" irrelevant cus

(Sp!;.cc., dc3cc;lo2 in Mac -',sh, 1965). Perhaps an explalatioi of the

ov-tr3i','l-; ::-.'-;1 effect involves both those processes. The

Douglas-Pritra-.. model su:. t,-s that this is so. In addition, the

results of this study Lay be as iiconsistsent with the Doublas-

Pribra r.. :1. as was first -.:i.:ted. The differentiation required in

the present sr .7 involves s.-ti-.l cues, a di:-.:ion thought to be high

on the rat's "..tsntic al hierarchy." If this is the case, the role of

the hi.poc : that of g.-nin out irrelearnt stimuli, would be

nir.al in the intact S, and Ss without the hippocampus should not be

greatly impairel. Perl.->o: a hi;.poc.-':.1 lesion-ir'duc'cd deficit would

be evident in the prc-s:-t r ..r-.]ig if a task involving a non-spatial

differentiLatio,_, or, more probably, a differentiation between a large

number of equ-...y saliojit cues was employe... Support for this possi-

bility is pr,'-,-: .-d by Pril:- _-_ (1969), Uho reports that bi.c-:..ctonized

monkeys show r.tar-L-tic) in discrimination 1 rning, provided there are









a .; nrm-.b.r of non-r' e.:a:3 I to:ZtiT:2s in the sit ti.on

(pS. 137).

A second procedural innovation e: loycd in the px- -.t stury

ir,.'lv,, s the rcspoose selectca foe- st.dy. Those studied, reported

prev-iouly, which h1 do: str ated the hippocnrnal lec.n re;vorr:1

deficit h-e typically e:ployc& an inst.rient-J. respo4s rcqu.irinC

sonc foriL of gross loccl otion on the part of S. In con'. -t, this

study utiliz7ct an 0oeiit response, a be, press, vliich, v.!I.: the

typical inst.r t-...I:a resp:.nes rqiies a ai.ii-i.: of locoCotion, ta':es

a short ti:sm to execute, requires relatively little effort, and leaves

S in th. s ... p>.ce rsy to resp:id a2ain. Althoal h it is go eral.ly



isU u'icr,-l-: t i appear to ta a.:loO cs ta;s in th tilo 1per -

metal approa-ches Cdo not differ in rany critical aspect, a thoro_ -A

cc_; :.isoin of these t'.o pr- -curs hs not yet be"n attempted. Hoveier,

a recent study by Means, "Ker, and Is ..,:: (1969) i: ic .tes th"at the

effect of hippocapal d.is,.'_.ion upon go-no go perform :.':e mray be

resp.:.--.-specific. Althoieui it is typically reported that hI, c, ca:pecto:.:y

interferes with this behavior when cxaZined in an instic..:;tal par...' .:A],

such as an allei. '.y (.o "., Kaufcan & KMrco, 1969), Means et al. rcep:rt

that hippoca:.,pal ablations facilitate performance in this task when a

bar press rc. :-,.I is utilized. Fin'lTir-3 such as these qu-.ti .,', the

trans-situational Lr:ture of the pattern of lbt';-ioral disruption ob-

serv...l following hippoce,-pal destruction and, consequently, an1' formu-

lation which attempts to :co.:';. for these effects with global concepts







su :h as 0'1-:.T ration," _.'.ir _," or "inhibition" without further

re D.--o it oir Qalificatio.

The third r'ajor di fe1rence tet,~ccn this and contemporary in-

.'.tiatic. s Of the role c_- the hippocarupis in discri. *- Ion learning

inyoli c-' the sche'lecs of reinflc::. nt associated with the two to-bCc-

discrimiiiated responses. -.:- reszc:. i -r. .d u iously has typically

p:-1 .ir .CI cont. .i c. rei' .. nt for "co -c'" r:'-.:.30es and withheld

rcl:.2.orceent for "incorrZct" r ..:::: ... In the pr...-, st .';, con-

C,..:cnt o;i :-:a: !s were utilized: Both respc:::- iere reinforced, one

on Ln FR 5 scLm'.le and t'. other on an l: 9 -s 'le, r':'. the fora'-

atiori of ths c'-cri- 'i.ticr- Was 'zbsed on a relat-.:, r.-' :: t n

al:-SDlute, dif fotial in rein for1e: 2t dJ.:ity. Tf;: e 7 j-ri it1

, -,vsis of concurrent ratio sch:,.iles inicates that with unequal FR

reqir-';.-ts, espoiing t: .' to be r-aintained only by the schedule

wizh the scal :FR requiT .. t; with equal F. requirements, responding

carn be naintai_-cJd by either one, and shifting fro c:,.: schedule to

the second oc.-.lonally c::i"v. (C-t'.1-., 1966, E-.2:rnstein, 1958). In

a study which i" only sup finallyly co: _.r.ble to the o.:- re cted

he7o, Douglas C.-. Prilr.. (1966) c-.::.in:.. the effects of probabilistic

reinforcc-r:ct -z:.r, the foi ::,tion of a disci ,.inatc.t pr-:.- press in

moaLeys. As 12 the present study the d'.crinination rested upon a

relative diff.-rer.tial in r:'iLfo'cc.1c:it dcisity; one response was

reinforced 70;' of the tine and the scc-;3 reinforced 30;3 of the time.

T'r ir results, in contrast to those of the present study, irUicat-ed

th:-t hip'co:::.-toized Ss "re retarded with respect to control Ss









in their ability to acquire a discrj.t.'. oi .ic- suc c itions.

fortui-r'tely, no data Ce snted oi the pcfor.- :.ce of thsc, Ss in

di inination revere. .. iL reasons for these eaprrently con"'. "ctoy

finding: are unno:7 ut thse0 st' dies ,. I that J. J Ciciet

attention: has bzan directed toia.' s C.T declaration of the eficcts of

sc''.lcS of reinfocrc-:ct on discrll.iration fori:.ltion ad.! reveirsl

in hippocp cctoriizd Ss.

Another difference b ,&en this a-I other studies of hippoc.::~ 1

functici involves the spc.ir.s of test trials. Most r.-c .rch in this

area !e.s employed a discrete trle proc: r & td ta-v related te ir Cue

of massed train trils d each daily e: irrcl s ion. In

the present study the e .ai. .nt of tc:t trials, the five '-nute free-

choice periods, wore ." ':ly spaced for they r. I. at the bseginir2

of each daily ex-peri ental se.ssion. No direct evidence is c :-,lable

conic-..i:- the effect of this factor on discriL.in:ation learning and

reverl.- in hippocampectoaized Ss. HO-. ., there is evidence that the

interval bete,:en trials does inf]i',: ".:- the bihavicral effects of hippo-

camipal disruption. As reported previously, Kirkby, Stein, Kimble and

Kimble (1967) have demonstrated that the lac- of T.-maze spontaneous

alternation co:'ionly reported in hippocan.pal Ss can be reestablished by

lengthening the intertrial interval froa 50 .si.. -os to 10 minutes.

Although their explanation of this ph'no-::.ion, a postulated lesion-

induced reduced infor-mtion ac uisition rate, has been generally
abandr,:.-i on the praise that :c.ch preparations do not show deficits in

a number of alter'.-tive learning tasks, no adcc.ate .pl:. -tion has l. .n







fo :.ated. Little or no *..tional research has i,: ..directed to':2r-3

an Tnderstanrig of this finding, and. until this phenomenon is investi-

:.'.:0 in i c :.., detail such an explanation of the results of the

pr..eent e.1,-:- :,t cjinot be fully evaluated.

A fifth majorr departure of this e ,:' :.. relative to previous

rec:: .rch is tnso utili :tion of a forced training technique. As a

function of fulfil.:I the requirements of the rcsponse-.reinforceent

contingentcies, this procclre ir.3.'edi that e..c' S was fully exposed to

the co:,.'.itions of reinforceent throughout both acquisition tan

re...-sal training. In addition it can be ass~nd thL.t this innovation

mo s prolc.bly raintained the strength of the FIZ 9 response at a

re. -.tively his,or level th..n discdieinnation studies which hwve not

e:.l-ed forceL tr-'. ong s.d reinfo7rcGent c. the "Incorrect"

reE--n-. Isa.:c.on, Olton, azuer and Svart (1966) present evi: :,.:

which indicate-s that t'rf;e hippocc,:i.pally lesioned S's inability to

with.l! a ret -.e in the passive; avoidance ta.': is directly related

to the strcnpt' of that response. It is also possible that the ease

with vhich hi( .:c:.:pctcmized Ss can inhibit one ic,,se and initiate

an alternative is dependent upon the relative strength, or probability,

of th.se two responses.

These findi~-3, which dc-onstrate that hlppocr-:p:l Ss are

capable of inhMCiting an e.t-,ablihed response and initiatir'3 another,

st&nd in ra--.'. contrast to the talkl of the data on the performance of

such Ss vihen f.- :- with similar tasks. It is not surprising that task

vari..-.bles, so--- of which have been discussed c,.cv, have the potential

to pr-ofoundly i-flue-ce the behavioral effect of physiological Lniru-

lations. What is surprising is that no concertcd effort has been made









to explain s-uc fir.ling: 't.thi:i the c7 f. ts cf pra "c.t fo 'L:latioC:s

of hippoca .pl fi icticn, or to ie-vise thL:se forulations so that thly

may incorporate t hse .. Its. M11 too often fiUlins as have

been disc,,l. hEsrc are neglected or dis:issec Ce aberrent. Pci-.aps a

detailed e:a iination of the n Tner in which exs? '.2-.l r 'nipulations

can chasge or counteract the effects of physiolcical c.rniil-ations '.Jill

provide increcad insight into th role of neuroTphysioloic.l1 systr -'s

in the intact or.u nis:.

The unexpected facilitation of discr:' 1- i,-: reversal per-

formance resulting froi tlhe necorticl, da'"-u: sustained by the

control Ss is most likely a.'.:.1t?.. le to m.control!ed position

prefe...es, v, ciscussi previously. O'thr se ri ent Stioi on t

effects of hip: c .l ablation has t:, icilly nvolv/d aalogous nec-

cortically lesior.u. control Ss, and has re~..I- rly reported that such

Ss do not differ fr1o their uno-.rate c-:. terparts. There are ex-

ceptic.:,:. to this ho::..cr, for Mearns, ot (1069) ha;e found that

destruction of the noocortex overiyl g the hippoc.. _,. leads to a

retardation of performance in the go no-go t:.:; and Olt':. c: Isaacson

(1967) have reported that d-.: -:e of this area, as well as this area

plus the hippocampus, lengthens response late!cies in avoid:-rnc a-:d

escape tasks.

In the present experiment neocortical e.dttiu;tion ir:,'lOed

considerable portio',s of the rat r..:',2ortex cc-L.;-.tr.ble to .170:" i's a c:'

7, which is involved in so.:..-,thesis, particularly the integration of

information on weight ar.n th- state of muscles vnd joints; areas 17








and 18, the vi -_1 projection and association -..-;-,, respectively;

area 25, the entor1:,-_ cortex; a:d area 37, which receives sz.; ;esthetic

&ud optic as-.:'-t.o-n fibers andq in ana, is thouiht to be involved in

the rcco n:ition c- body i 9', indivi-' ty continuity of

per:----lity a1nd of the self in relation to the E .vironment (Kreig,

1957). Since a considerable portion of the hi .:.-. pal research has
involved so.~a (dOe of these arCes it is possible that co-o.only ob-

served hippo( ..:.! lesion deficits ePL0 in actuality a function of an

intr action of the hippoc"npus and the ne.ccn. 't.ex ,lhich overlies it.

Within this context, Ir-.,: .- (1967) has obsrvd that electrolytic

lesions i ::.tricted to the hi-poc- c friaently do _..t produce the

deficits seen in ablttion studies involve 2 neocorticAl destructirc .

It is also possible that thV facilit'nted pertorLance shoWn by the

hippoc,. .:ctoeizcd Ss in the present sti. is fully accounted for by

the effects of .::o0tical dcstLrction. Questio.!vi such as these point

to the relative prinitiveness of our U..i': t.:Ti,., of the role of the

hippoc-:iPu--; in behavior, and to the importance of further research in

this area.















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65

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66

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Michael Arnold Mirlan '.s lorn on January 25, 1938, at New York,

New Yorl:< He attended -.Ll"c school in e":', Yo': state and gradetcd

from F.- yetteville-!anlius High School, Fayette671e, Nce' York, in

June, 1956. In May, 1960, he received the dc-rs of _1-.'..lor of Arts

froi Si.:. :e University. Froi 1960 until 1962, he sez.,il in the

Adjutant General Corps of the United States Amy. Follo'.ing his release

fr:i the Aany khe uas cnploycd ,s a psyc'.:-lojic.l research assistant

with the Veteran's A1:1nistration EospitJl in Syracuse, xe' Yor'k. In

Septe:.ct.i', 1963, he enroll~i in the gr -to s:' ool of the Univer~'.i

of Floridfa an r :eceivcd the Master of Arts d:rca in Decehber, 1965c He

served a- a r:.:.. .'ch assistant for Dr. H. S. Pe;:. -: .e and as an
interim inst-auctor With the I-:. rtnnt of P: L'c-.'l.- while r;triculating

for the Doctor of Philosophy degree in i:, chology.


BIOGRAPHICAL S (.-,C:'










This dissereNtion .:as prepared undel the direction of the chair-

man of the candidate's sup rvisory cc... .:ttee oand has been approved by

all cx'Abe'rs of that committee. It vas subLitted to the Dcan of the

Collo-s of Artt aind Sciences anid to the Gi..' to C: -'c l, a,. :?s

approved as pa:.tial fu fill3eent of the requirements for the dcgric of

Doctor of Philosophy.











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