MIDBRAIN RETICULAR STIMULATION
AND GENERALIZED DRIVE
CHARLES JOHN VIERCK, JR.
A DISSERTATION PRESENTED TO THE CRiDUL.TE COUNCIL Or
THE UNIVERSITY OF FLORIDA
IN PARTLIL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
The author wishes to express gratitude to his
Chairman, Dr. Frederick A. Kins and to Dr. Robert L. King
for their valuable suggestions and assistance. Special
appreciation is also due Professors B. N. Bunnell,
D. C. Goodman, and W. B. Webb for their assistance as
members of the doctoral committee.
TABLE OF COIITENTS
DDICATION LEDG .. . . . . . . . 1
A.CY U ;OW:LEDGME; NT S .i....... ... ii1
LIST OF TABLES . . . . . . . . v
LIST OF ILLUSTRATIONS . . . . . . vi
IITRODUCTION .. . . . . . . . . 1
METHOD o . o o o e.. e. e o o o 7
Subjects . . . . . . . 7
Surgery . . . . . . . . 7
Stimulation . . * . . . 8
Electrocorticogr recording * * * 9
Gross observations . . . . . . 10
Behavioral tasks . . . . . . 10
Gross activity (GA) . . . . . 10
Fine activity (FA) . . . .. 10
Exploration (EX) . . . . 11
Food reinforcement (FR; FRS) . . 11
Sidman avoidance (AV) . . . . 12
Stimulation valence (VAL) . . .a 12
Behavioral testing procedures . . . 13
Histology . . . .. . . ... 14
RESULTS . . . . . . . . . . . 15
ECG activation . . . . . . . 15
Gross observations . . . . . . 17
Behavioral tasks o . a 19
Histology ..... ..... . . . 24
DISCUSSION . . . . . . . . 26
SUMMARY . .. .. ..... . . 32
BIBLIOGRAPHY . . . . . . . . . 33
APPENDIX * . . . . . 42
LIST OF TABLES
1. Average differences between stimulation (S)
and non-stimulation (NS) scores for each
task and at each intensity of stimulation . 21
2. Treatment (S vs. NS) by treatment (uA) by
subjects analysis of variance, showing F-ratios
for the two main effects and the interactions
between these effects . . .... .. 22
LIST OF ILLUSTRATIONS
1. Electrocorticogram recordings, illustrating
arousal induced by reticular stimulation . 16
2. Behavioral performance without stimulation
and as a function of increasing intensity of
stimulation . . . . . . . . 20
3. Diagrammatical representation of electrode
tip placements in the dorsolateral midbrain
reticular formation . . . . . . 25
The idea that reticular activation and generalized
drive might be functionally related has been stated by
Berlyn (1960), Dell (1958), Hebb (1955), Lindsley
(1951, 1958, 1961), malmo (1959), Morgan (1957), and
Schlosberg (1954). For example, Hebb (1955, p. 249)
has stated that ". .. arousal .. is synonomous with
a general drive state .," and Dell (1958, p. 196)
has remarked that "It [the reticular formation] provides
the active source of continued excitation referred to
by psychologists as 'motive', 'sensitizing component',
On the basis of psychological data, Brown (1953,
1961) has argued convincingly for the concept of drive
that includes an intensity dimension but no directive
function. A similar view has been expressed by Duffy
(1951, 1957). According to the theoretical formulations
of Hull (1943) and Spence (1956), an increase in nonspecific
drive level will heighten the vigor and/or efficiency of
ongoing behavior, regardless of the particular source of
the drive. Thus, if the reticular formation (RF) serves
as a central mechanism for generalized drive, direct
stimulation of this region should produce performance effects
identical to those brought about by manipulation of
motivational variables. That is, a wide variety of
behaviors should be affected by reticular stimulation
regardless of the source of drive employed during
training, and the nature of the performance change should
parallel that produced by an increase in drive from any
There is a great deal of indirect evidence support-
ing a correspondence of reticular activity with drive level..
Bolanger and Feldman (reported in I1almo, 1959), Duffy (1932),
Freeman (1948), Lindsley (1958, 1961), and Steiner (1962)
have shown a direct, though sometimes nonmonotonic, rela-
tionship between various physiological measured of arousal
level with performance level and/or drive.
Increased attention is presumably a correlate of
high drive states, and Galambos (1954, 1956), Granit (1955a,
1955b), Hagbarth and Kerr (1954), Hernandez-Peon et al.
(1956), Kerr and Hagbarth (1955), and Rasmussen (1946, 1953)
have demonstrated reticular control over sensory input
from a number of modalities. In this manner information
through one or several sense modalities can be inhibited
by means of reticular influences, thus reducing irrelevant
noiso and allowing focus of attention within one modality.
In addition, high drive states are characterized by
increased sensitivity and reactivity to environmental
stimuli. Fuster (1958), Fuster and Uyeda (1962), and
Isaac (1960) have reduced reaction time with direct
reticular stimulation, and Lindsley (1958, 1961) has
shown the same phenomenon with cortical desynchronization.
Reticular stimulation has also been shown to increase the
resolving power of the cerebral cortex (Lindsley, 1958,
1961) and to lower thresholds for tachistoscopic perception
(Fuster, 1958; Fuster and Uyeda, 1962).
A number of studies dealing with humoral and drug
effects on the RF and behavior have supported the drive
proposition. Bonvallot ct a,. (1954), Courville et al.
(1962) and Dell Lt al. (1954) have shown that adrenaline
stimulates the RF and producer cortical arousal. In
addition to the well known role of sympathetic activity
in emotional behavior, it has been demonstrated that
motivational states of asphyxia (Bonvallet ct al., 1954;
Dell et a., 1954) and hunger (Holzbsuer and Vogt, 1954)
increase adrenaline output. Also, Sawyer (reported by Dell,
1958) found that estrus decreased the threshold for cortical
arousal with RF stimulation. Bradley (1958) has produced
EEG activation with amphetamine and has localized its
effect in the reticular formation. A number of behavioral
studies have reported a facilitating effect of amphetamine
upon performance (Dews, 1958; Morse and Herrnstein, 1956;
Skinner and Heron, 1937; Uyeda and Fuster, 1962; and
Wentink, 1938), although exceptions exist (Kelleher and
Cook, 1959; and Owens, 1960). Chlorpromazine has been
shown by Killam and Killam (1958) to depress reticular
arousal, and Posluns (1962) presents data and cites 13
studies demonstrating inhibition of avoidance behavior and
activity with chlorpromazine.
AlthouGh the above evidence lends impressive
support to the drive hypothesis, very few studies have
tested the effects of direct reticular stimulation in
situations Thcre manipulation of deprivation time or
intensity of noxious stimulation have been utilized to
establish the concept of generalized drive. In fact,
the studies which most closely approach this procedure
have reported inhibitory effects of the stimulation.
Stimulation of various cerebral structures capable of
producing cortical arousal has been shown to inhibit or
impair both learning and performance of complicated choice
behaviors (Gliclman, 1958; rIahut, 1962; Milncr, 1954;
Proctor et al., 1957; Rosvold and Delgado, 1956; and
Thompson, 1958). The areas stimulated in these studies
were: medial and intralaminar thalamic nuclei, brain
stem RF, posterior hypothalamus, and caudate nucleus.
Though these results seem contrary to the drive hypothesis,
they may indicate interference with memory rather than
In order to study adequately the drive mechanism,
rate measures of simple or unlearned responses should be
used. In studies of this nature, Chiles (1954) found
inhibition of bar pressinS for food with medial thalamic
and posterior hypothalamic stimulation, but Mahut (1962)
found no effect on running speed or eating behavior with
thalamic and brain stem reticular stimulation. Grastyan
et al. (1956) applied stimulation to the posterior hypo-
thalamus which facilitated defensive conditioning and
inhibited alimentary conditioning. Bloch and Hcbb (1956)
abolished a simple avoidance response with intralaminar
thalamic stimulation, but reticular stimulation had no
effect. Sheer (1961) found no effect of posterior hypo-
thalamic stimulation upon a conditioned flexion "esponoe,
delayed reaction performance, or bar pressing on a VI
schedule for food. Ingram (1958) inhibited bar pressing
for food with posterior hypothalamic stimulation, but not
with caudate stimulation. Finally, to complicate the
picture further, Ehrlich (1963) found that tegnental
lesions decreased rate of bar pressing for food or water
but increased rate of running to obtain food.
In the present study, the midbrain RF was stimulated
while animals performed a variety of simple tasks that have
been shown to be sensitive to drive effects. Different
incentives were sampled in order to test the generality of
drive effects that may be produced. Motivational studies
that pertain to the tasks used are as follows: (a) Gross
locomotor activity is increased under conditions of food
deprivation (Hall and Hanford, 1954; Siegel and Steinberg,
1949; and Strong, 1957). (b) Fine activity as seen in the
groominG and scratching behavior of animals is decreased by
deprivation (Stro%:g, 1957). (c) The experiments of Alder-
stein and Fchrer (1955), Dashiell (1925), Fehrer (1956),
Thompson (1953), and Zimbardo and Hiller (1958) have
indicated that high drive increases exploration of a noval
environment. (d) Dinsmoor (1952) and Forster and Skinner
(1957) found that increases in deprivation increased the
rates of bar pressing on VI and FR schedules respectively.
Also, Webb and Goodman (1958) trained animals to press a
bar for food, then satiated the Ss and found thai covering
the floor with water increased the rate of bar pressing.
(e) Amsel (1950) and Boren et jl. (1959) have demonstrated
that increasing the intensity of shock or adding hunger
increases the vigor of avoidance behavior.
Twenty-four male, Long Evans, hooded rats of
approximately 70 days of age were obtained from Harland
Small Animal Industries. SurGory was performed on all
animals of this group, and eight of the rats underwent
part or all of the behavioral testing. The experimental
subjects were selected primarily on the basis of a lack of
forced motor movement from stimulation up to at least
150 uA of current. Other factors such as death and
dislodging of electrodes further limited the number of
At about 90 days of age, the subjects received
surgical treatment under nembutal anesthesia injected
intraperitoneally at a dosage of 60 mg/kg. Each rat was
also given 0.2 mg of atropine sulfate intraporitoneally
and 60,000 units of penicillin G intramuscularly. The
skin on the dorsal surface of the skull was incised and
the skull was entered with a 4!2 trephine. A bipolar
electrode of the type described by Valenstein etal. (1961)
was lowered stereotaxically into the RF through the
trephine opening, according to measurements obtained from
De Groot's coordinates (1959). The coordinates used for
the reticular electrodes of the eight experimental animals
were 2 mm lateral to the midline, 0.5 mm anterior to the
0-0 point, and 6 mm in depth from the surface of the
cerebral cortex. Variations of 0.5 mm in the anterior-
posterior and dorsal-ventral dimensions were introduced
in several animals. Reticular electrodes were placed
on the right side in 5 experimental Ss and on the left
side in 3 animals.
Three stainless steel electrodes, bent at a
90 degree angle 2 mm from one end, were hooked under the
skull through small drill holes for supradural electro-
corticogram (ECG) recording. The recording electrodes
were placed over the frontal, parietal and occipital
areas of the side opposite the stimulation electrode.
Stainless steel screws were placed in additional drill
holes to serve as binding posts for acrylic cement which
was used to attach the electrodes to the skull. The skin
was closed around the electrodes, leaving an exposed area
of acrylic. The wound, however, healed well, and infection
was not evident.
Electrical stimulation was delivered to the reticular
formation by a Grass model S4E stimulator which was set to
provide a train of biphasic pulses of 0.1 msec duration
at a rate of 60/sec. The stimulus was fed through an
Argonaut isolation transformer. Current and voltage
were monitored on a Tektronix Type 502 dual-beam oscillo-
scope, and readings were taken from the trailing dodge of
the distorted square wave. Calculated electrode resist-
ances ranged from about 20,000 to 30,000 ohms.
Electrocort icogragm recording
Connections to the cortical recording electrodes
were achieved by attaching miniature pin clutches soldered
to lead wire. Two Grass Model 5P5 polygraph channels were
utilized in obtaining records from frontal-parietal and
parietal-occipital leads. The average resistance between
electrodes was 20,000 ohms.
ECG testing was first carried out as the animals
recovered from surgical Ilembutal pentobarbitall sodium).
Later, at 250 and 400 days of age, the animals received
further testing after injection of 100 mg of Robaxin
(methocarbamol). Robaxin presumably acts upon internuncial
neurons of the spinal cord, thus facilitating relaxation
and drowsiness. Predominantly high amplitude, slow ECG
activity is obtained after injection of Robaxin, and
arousal from either reticular or natural stimulation
occurs more readily with this drug that it does with
Each animal received RF stimulation in an ascending
series of 0.5 volt steps, starting at 1.0 volt and ending
beyond the ECG activation threshold. This threshold was
defined as the point at which high amplitude, slow activity
was completely obliterated by low amplitude, fast activity.
After the initial determination of threshold, a number of
activation tests were carried out at voltages bracketing
On four different occasions, RF stimulation was
delivered in an open field for the purpose of observing
behavioral signs of arousal. Strength of current was
varied in ascending and descending stops of 0.5 volts.
The animals' reactions to external stimuli were tested
with and without RF stimulation by the following
manipulations: (a) The subjects were handled by the
experimenter; (b) a pencil was moved before the
subjects' faces to test visual following; (c) the
animals were lightly prodded and tapped with the pencil;
and (d) the experimenter clapped his hands to produce
an auditory startle response.
Gross activity (GA):- The animals were placed in
an alleyway 24 in. long and 8 in. wide containing photocells
that projected across the midpoint of the long sides. A
count was obtained each time the rat interrupted the beam,
and number of counts was the criterion measure for activity.
Fine activity (FA):- Fine activity was measured in
a tilt cage consisting of an 8 in. diameter cylinder
pivoted at the center of its base. Four metal posts,
equidistantly placed on the periphery of the base and
several mm below the level of the pivotal post, mode
electrical contact with metal plates affixed to the base.
Opposed sets of contacts recorded on the same counter,
and an animal's score consisted of the total counts
registered on the two counters. This apparatus was ex-
tremely sensitive and would count out rapidly for small
movements ouch as those scon with grooming behavior.
Exploration (Ej:':- The purpose of this task was
to determine the number of times subjects would approach
a novel object and the amount of time they would spend
examining it. Scores for the task were obtained by
summing the number of approaches and the time spent
sniffing or touching the object. The enclosure u-t.- was
24 in. in diameter and contained an interestingg" object
that protruded from the center of the floor. The object
consisted of a 6 in. high metal spire emerginG from con-
centric cylinders 3/4 in. and 1 1/2 in. in heiGht. Follow-
ing each two days of testing, another part was added to
the spire to ma:1ntain novelty. First a spring was attached
horizontally from the top, then a yellow wire was hung
from the end of the spring, and finally a small bolt and
nut were attached to the free end of the wire.
Food roinforceaent (FR; FRS):- The animals were
trained to obtain 45 mg Noyes lab rat food pellets by
pressing a bar protruding from one wall of a 12 in.
square enclosure. Five subjects were trained on a variable
interval (VI-30) schedule with a range of five to 55 seconds,
and the remaining two animals were trained on a high fixed
ration(FR-150) that produced strain. The animals were
maintained on an 8-12 hour food deprivation schedule (FR)
in order to keep the motivational level low but effective
in maintaining stable rates of performance. All subjects
were also tested under food satiation (FRS) on an FR-5
Sidman avoidance (AV):- The animals were trained
to avoid shock to the feet by pressing a bar projecting
from one of the short walls of a 12 in. by 6 in. enclosure.
The apparatus was dimly illuminated through 1/2 in. holes
above the bar and in the top of the enclosure, and through
a translucent glass window in the wall opposite the bar.
The apparatus was programmed so that electric shock was
delivered through a grill if 30 seconds elapsed after a
bar press or a previous shock (SS-30-RS-30 schedule).
The shock was maintained for a maximum of five seconds and
could be escaped by a bar press. Four animals were given a
1000 cps tone and light through the window as warning
signals that preceded shock by five seconds and remained
on until shock was terminated.
Sti~ul'.tion valence (VAL):- A test of whether RF
stimulation was positively or negatively reinforcing was
given in which the animals could choose between stimulation
and no stimulation. A shuttle box was divided by a 2 in.
high barrier into two 9 in. by 9 in. compartments with
independent brass grill floors. The floors were pivoted
at one end and suspended by spring tension at the other so
that the weight of an animal tripped a microswitch. The
microswitches controlled relays that allowed recording of
the time spent in each compartment (the criterion measure)
and directed reticular stimulation to the animal only when
he was in a particular compartment. The stimulation
compartment was changed from day to day.
Behavioral testi g procedures
On all tasks except stimulus valence, the subjects
daily received ten minutes of testing with stimulation and
ten minutes without stimulation. Five minute stimulation
(8) and non-stimulation (US) periods were counterbalanced
in the order S-S-NS-S- or ISS--S-1S. Four consecutive days
of testing were given at each stimulation level with the
two counterbalanced orders being alternated over days.
The stimulation values used for testing were given in the
order 10, 25, 50, 75, and 125 uA, with occasional commission
of some levels. For stimulus valence testing, an ascending
series was given with two days at each current intensity,
followed by a descending series. The intensities of
current utilized with each task are indicated in Table 1
of the Results section.
If an animal exhibited consistent facilitatory
effects of the stimulation, he received an additional four
days of testing at the stimulation intensity and tas]:
showing the effect. Consistent facilitation was defined
as facilitation occurring on three days out of the four
days of testing on one stimulus intensity and task.
Behavioral testing was bogun at 120 and continued
to 400 days of a6e. The number of subjects run for all
tasks can be found in Table 2. The order of presentation
of tasks to the subjects was randomized except that gross
activity vwas the first task and stimulus valence was the
last. For food reinforcement and avoidance, the subjects
were trained to a stable level of performance before
stimulation testing was begun. Training prior to testing
was not required with the remaining tasks.
At the end of the experiment, the brain of each
animal, with the electrodes intact, was perfused and fixed
in formalin. The electrodes were then removed, and the
brains were embedded in celloidin. Serial, coronal sections
of 30 micra thickness were cut and appropriate sections
were stained with cresyl violet.
Reticular stimulation of all animals proved capable
of changing high amplitude, low frequency eloctrocortical
activity to the low, fast, desynchronized pattern typical
of activation. Cortical activation thresholds as deter-
mined under surgical anesthesia averaged 120 uA. Testing
at 250 days of age after injections of Robaxin revealed
a lower mean threshold of 40 uA in seven of the animals.
The range for these animals was from 25 uA to 60 uA, and
threshold for the eighth rat was 260 uA. The thresholds
of four animals were obtained at 400 days of age, also
under Robaxin, and an average rise intthreshold of 25 uA
was observed. The latency of observable activation was
typi.:Jlj about one second, and return to high voltage,
slow waves usually required approximately two seconds
after termination of stimulation. Several animals received
stimulation for five minutes and activation was maintained
throughout the interval with the usual latency of return to
high, slow activity. Samples of reticular induced activation
are presented in Fig. 1.
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The first grossly observable reaction to RF
stimulation typically occurred at a threshold of approxi-
mately 50 uA and appeared to be a generalized "alortins".
This response involved some or all of the following com-
ponents: (a) a halting of grooming or perambulation,
here referred to as "freezing", (b) forward movements of
the pinnae, (c) vigorous movement of the vibrissae and
sniffing, (d) exaggerated, irregular respiration,
(e) fixation of the head with apparent visual staring, and
(f) occasional grinding of the teeth. At 75 uA, external
stimuli were presented and produced responses which deviated
only slightly from those elicited in the non-stimulation
animal. The subjects reacted as usual to handling with no
exaggerated struggling. A loud auditory stimulus (hand
clapping) produced normal startle responses. Orienting
was occasionally seen when a pencil was slowly moved
in front of the animals or when it was used to deliver
a tap to their backs. More commonly, however, the visual
and tactual stimuli were ignored with a relative absence of
visual following or turning toward the side tapped.
Within a range of 100 to 250 uA responses were
elicited that appeared to be of a "fearful" nature. This
involved an increase in muscular tone, freezing into a
huddled posture, and occasional bursts of activity in which
the animals backed up to a wall or into a corner. Alerting
was pronounced, and the So appeared to shrink from an
imaginary threat. Several animals would alternately huddle
in a corner and vigorously back across the floor to another
wall or corner. The animals seemed to ignore visual and
tactual stimuli and did not attack or avoid objects placed
before them. Auditory startle responses were observed.
Upon handling, strong attempts wore made to escape the
restraint, and biting sometimes occurred.
When the fear response became intense, within a
range of 150 to 250 uA, five of the animals leaped
spectactularly up the sides of the enclosure. These
jumps did not appear to be directly forced by the stimula-
tion. The responses were not stereotyped, coordination was
excellent, and the jumps in all cases were well directed
toward the top edges of the box. Also, it was discovered
that leaps did not occur when the subjects were stimulated
while on the laboratory floor, free from restraining walls.
In this latter case vigorous running occurred as if designed
to escape the vicinity of stimulation.
Forced motor movements were seen between 150 and
250 uA. Six animals exhibited a contralaterally directed
concavity of the body and turning of the head. In three of
these cases, contralateral circling and/or leaning appeared,
but the other three subjects turned Ipsilaterally. Thresholds
for the responses observed in these animals usually appeared
in the order: alerting, fear, forced movement, and jumping.
At threshold current for forced movement, the circling
and body concavity could be compensated, and the movements
were interrupted by return to normal standing posture.
Jumping behavior usually occurred concurrently with forced
movement but also appeared in animals not showing the latter.
The predominant effect of reticular stimulation
was to inhibit ongoing behavior, as shown by lower scores
during stimulation. This effect was consistent among
subjects and was significantly present for GA, EX, FA, FR,
and AV. As seen in Fig. 2 and Table 1, the amount of
inhibition increased from 10 uA through 125 uA, and the
majority of significant effects were obtained at the higher
intensities. The stimulation also became increasingly
noxious as current was increased. Table 1 gives the
average difference score (minus signs indicating inhibition
and plus signs indicating facilitation) for each task and
at all current levels. In Table 2, F-ratios are given in
analysis of stimulation effects over all currents, effects
between the several stimulation intensities, and the inter-
action effect between the two treatments.
6 GROSS ACTIVITY
43 0 .............. ............... ... .......
2 0O. .-..., *.
... ......... ......
FOOD REINFORCEMENT (UNDER DEPRIVATION)
..50 ... .............0..
c 350- -... *
110 FOOD REINFORCEMENT (SATIATED)
o 190 .........................
o I O .......... .
15 0 -.*
180 STIMULATION VALENCE
S I00- ...... ..OO
60 ........... .................. ......... ..........
10 25 50 75 125
Stimulalion Current In L.A
Fig. 2. Behavioral performance without
stimulation and as a function of increasing Inten-
sity of stimulation. Each point represents an
average group score over four days of testing.
Stimulation scores are connected by broken lines,
and non-stimulation scores are joined by solid
lines. Statistical probability of less than 5%
as determined by the randomization test for matched
pairs (Siegel, 1956) is indicated by the symbol (*).
Average differences between stimulation (3) and non-
stimulation (NS) scores for each task and at each intensity
of stimulation. Hinus (-) signs indicate greater number of
bar presses or activity and exploration counts during the
lS periods. Plus (+) signs indicate the opposite.
Hinus signs for valence of stimulation indicate more time
spent without stimulation. Abbreviations are as follows:
GA gross activity, EX exploration, FA fine activity,
FR food reinforcement, FRS satiated food reinforcement,
AV Uidman avoidance, VAL valence of stimulation, and
D average difference scores.
10 uA 25 uA 50 uA 75 uA 125 uA
GA D 7.4 5.9 15.2 24.7* 33.3*
EX D 13.3 32.3*
FA D -328.31*
FR D 13.4 37.4* -127.3 -201.9*
FRS D 1.4 + 4.2 14.2
AV D + 10.7 24.0 37.9* 39.3 -113.4'
VAL D 15.3 63.7 75.8 -114.9*
indicates statistical probability of less than 5% as
determined by the randomization test for
Treatment (S vs. 113) by treatment (uA) by subjects analysis
of variance,a showing F-ratios for the two main effects and
the interactions between these effects. The abbreviations
are as in Table 1.
I1 S-JNS (df) uA (df) S-1S5 x uA (df)
GA 8 5.53 (1/7) 0.65 (4/28) 2.17 (4/28)
EX 7 5.50 (1/6) 2.54 (1/6) 2.30 (1/6)
FR 7 6.75* (1/6) 2.41 (3/18) 2.34 (3/18)
FRS 5 0.05 (1/4) 1.60 (2/8) 0.30 (2/8)
AV 7 6.04* (1/6) 0.04 (4/24) 3.80*(4/24)
a The statistical analysis was taken from
indicates statistical probability of less than 5%.
Undoubtedly, the attainment of statistical signifi-
cance of reticular inhibition has been made difficult by
several features of the experimental design. For example,
the variability of scores was increased for the food rein-
forcement and Sidman avoidance tasks by changing the
conditions for some of the animals. This was done in an
attempt to find a procedure that might be sensitive to
facilitatory effects of stimulation. Also, the variability
of scores was probably increased by testing the animals,
in most cases, under low levels of drive. Weak current
levels were chosen with the expectation that facilitation
would occur at these levels if at all. Preliminary testing
with several animals at current values just below threshold
for jumping and forced movement indicated that these values
produced dramatic inhibition of performance. In view of
these factors, a nonparametric, randomization test was
used for the analysis of differences between S and VS
scores at each current level of each task.
As seen in Table 2, significant inhibition of bar
pressing over all current intensities was found for avoid-
ance and food reinforcement. In addition, the significant
interaction for avoidance was produced by an increasing
number of ND bar presses from 10 to 125 uA and a decreasing
number of S presses. This same trend was observed with all
other tasks except FRS.
Retests of animals showing consistent facilitation
over four days at a particular current level and task did
not reproduce the facilitation in any case. The average
of six retest scores was -28.2. No one animal or task
was repeatedly represented in the reruns. All but one
instance of original facilitation occurred at 10 or 25 uA.
One animal that was tested for 16 days on FR at 10 uA
exhibited a consistent and significant facilitatory effect
of stimulation. This animal did not show the facilitation
in any other situation and, in fact, was markedly inhibited
by the stimulation in many cases.
In general, valence of stimulation scores revealed
an increasing aversiveness of the stimulation from 10 to
75 uA. Only one animal preferred the stimulation, and this
effect was prominent only at 25 uA, changing to aversive-
ness at 50 and 75 uA. The only consistent effect observed
for this animal at 25 uA was inhibition of exploration.
Two animals revealed no marked seeking or avoidance of the
stimulation at any current level but distributed their
choices randomly. Both those animals were considerably
inhibited by stimulation on several tasks, primarily at
75 uA and above, but on one occasion at 25 uA.
The reticular electrode placements, as verified
histologically, are diagrammatically presented in Fig. 3.
The range of placements was 5 to 6 1/2 mm ventral to the
cortex, 1.5 to 2.5 mm lateral to the midline, and 0.5 to
1.5 mm anterior to the 0-0 point. The placements were
closely grouped, and all were within the dorsolateral
Fig. 3. Diagramuatical representation of
electrode tip placements in the dorsolateral mid-
brain reticular formation. Dorsal-ventral and
lateral dimensions are indicated in m. The draw-
ing is taken from De Groot (1959, p. 37), and the
level of section is 0.5 mm anterior to the 0-0
point. Distances anterior to the 0-0 point are
indicated by solid circles (0.5 mm), open circles
(1.0 mm), and a square (1.5 mm).
The grossly observable alerting effect has been
noted by a number of investigators and appears to be an
invariant response to reticular stimulation of moderate
to high intensity. It is interesting though, that the
alerted animals in this study were loss responsive to
external stimuli. This was seen as a diminution in visual
following, orienting to a tactual stimulus, and exploration
of a novel stimulus. The alerting may be comparable to the
arrest reaction produced by Hunter and Jasper (1949) to
intralaminar and medial thalamic stimulation. The thalamic
reaction seems to be more extreme, however, since Hunter
and Jasper saw no auditory startle response or visual
The forced contralateral head turning and body
concavity is contrary to the ipsiversive tegnental response
that has frequently been reported (see review by Skultety,
1962). Turning or circling was variable in the present
study and does not remove the discrepancy. However,
Skultety (1962) found contralateral turning with dorsolateral
midbrain placements in the cat that correspond roughly with
those of the present study. Eased on his work and that of
Sprague and Chambers (1954) with lower brain sten placements,
Skultety proposed a medial (ipsiversive)-lateral (contra-
versive) division that is supported in part by the present
Behaviors very similar to the fear reaction of
this study have been evoked by a number of investigators
from diencephalic and midbrain structures (Delgado, 1955;
Delgado et al., 1954, 1956; Fernandez De Molina and Hun-
sperger, 1959, 1962; Masserman, 1941; Roberts,(19%8, 1962;
Segundo et al., 1955; and Spiegel et al., 1954). Roberts
and Delgado et al. have shown that animals can learn to
avoid stimulation of "alarm" points in the dorsomedial and
lateral thalamus, the tectal area, the medial leaniscus,
and the inferomedial hippocampus, though avoidance learning
was not obtained from "flight" points in the posterior
hypothalamus. If tegmental stimulation produces a true
fear reaction, as these studies suggest, then it would
seem that avoidance performance should have been facilitated
in the present study.
The inhibition of reticular stimulation upon
performance was consistent, with the exception of one
animal showing facilitation on the VI-30 schedule at 10 uA.
Valence of stimulation was not determined for that animal
because of early death, and neither his electrode placement
nor behavior on other tasks give a clue to the reason for
this isolated finding. Roticular stimulation became
increasingly noxious and increasingly inhibitory as current
was increased, but a causal relationship should not be
assumed. Two animals demonstrated behavioral inhibition
with no evidence of escaping the stimulation. It is also
interesting to note that significant inhibition occurred
with fine activity and food reinforcement at 25 uA, which
was below the average ECG arousal threshold. This is not
particularly surprising, however, since that stimulation
was delivered to an awake, aroused animal.
It is improbable that reticular induced inhibition
is specific to certain parameters of the electrical stimulus.
A wide range of current intensities was sampled in the
experiment proper, and frequencies from 1 to 300/sec
were used in preliminary testing on gross activity.
Facilitatory effects were not observed throughout the
frequency range. In moot cases, tegmental stimulation
did not abolish activity, exploration, or operant behavior
but decreased rate to a degree related to the intensity
of stimulation. That is, the correspondence of amount of
inhibition with current value was not the result of
averaging data of an all-or-none nature.
Studies showing facilitation of performance with
drug intervention or spontaneous, generalized activation
are not conclusive evidence of reticular mediated drive,
since the cerebral structures involved in the initiation
of this arousal are not definite. The studies of Lindsley,
Fuster and Isaac, demonstrating enhancement of reaction time,
perception, and cortical receptivity with direct RF stimu-
lation, are more difficult to reconcile with the present
study. Unless species differences are a crucial factor,
it appears that reticular stimulation facilitates perceptual
processes and inhibits performance, and reasons for this
apparent contradiction must be sought.
It is probable that stimulation in the reticular
substance near the medial lemniscus and collicull produces
sensory effects including pain. In fact, Spiegel and
Wycis (1961) have stimulated the reticular formation of
humans subsequent to midbrain spinothalamic lesions, and
elicited reports of pain which was projected to the opposite
side. Such pain could elicit the fear reaction, and either
or both factors would serve as distracting influences to a
performing animal. Even in an avoidance situation, bar
pressing to avoid shock might extinguish during stimulation
periods, since relief from centrally elicited pain and fear
is not achieved. It would seem that such distracting
influences should have also impaired performance in Fuster's
study of tachistoscopic perception, but the nature of the
task and the response required may play an important role.
Fuoter's animals were well trained, and the response was
a discrete occurrence following upon observance of only
one of the briefly illuminated objects. Possibly a dis-
tracting stimulus must be intense to inhibit this reaction
as compared to repetitive, sequential, or complex responses,
which may be disrupted by relatively mild stimulation.
Also, the arrest of activity and alerted posture resulting
from RF stimulation might conceivably enhance perception but
antagonize maintenance of a steady rato of responding.
Another source of explanation is offered by the
inverted U hypothesis of arousal proposed by Malno (1958).
He has reviewed evidence indicating that intense rctivation
impairs performance on tasks measuring rate of performance
and vigilance. Two factors may be of importance here:
(a) The effect has not been demonstrated with tasks involv-
ing discrete trials widely spaced in time, and (b) it may
be difficult to produce subtle increases in activation with
electrical stimulation. The latter point, however, was
not supported by the ECG activation records obtained in
this study. ECG arousal did not appear to be an all-or-none
phenomenon, but as stimulating current approached threshold,
amount of low voltage, fast activity increased until high
voltage, slow activity was obliterated.
Several other possibilities should be considered
for future research. It is conceivable that direct chemical
stimulation of the RF would more closely simulate natural
arousal than electrical stimulation. According to Rinaldi
and Himwich (1955), and Stoiner and Himwich (1962), arousal
can be obtained with adrenergic stimulation in the pontine
reticular formation, and cholinergic stimulation in the
mesodiencephalic activating system.
Also, in view of recent evidence suggesting anatomi-
cal and functional differentiation within the brain stem RF
(Batini et al., 1959a, 1959b; Batsel, 1960; Bonvallet and
Bloch, 1961; Brodal, 1957; Feldman and Waller, 1962;
Huttenlocher, 1961; Jouvet, 1961; and Schlag et al., 1962),
a more detailed exploration of specific reticular areas
with electrical stimulation may be of value. In this
regard, it should be noted that Fuster found facilitatory
effects with dorsal midbrain placements comparable to those
of the present study. Nevertheless, there remains the
possibility that separate reticular areas differentially
express perceptual and motivational functions.
Eight animals were stimulated within the dorso-
lateral midbrain reticular formation while performing
in situations designed to be sensitive to variations in
drive level. Amount of gross activity, fine activity,
exploration, and bar pressing to obtain food and avoid
shock was suppressed as an increasing function of stimulat-
ing current from 10 to 125 uA.
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with reticular stimulation, and grossly observable alerting,
fear, and forced motor reactions were described. The reward
value of stimulation was tested in the majority of animals,
and an increased tendency toward escape of the central
stimulus was seen with increasing amperage.
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excitation does not produce the expected increase in
motivational level that would be evidenced as facilitation
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Charles John Vierck, Jr. was born July 6, 1936
in Columbus, Ohio, and attended public school there until
graduation from Upper Arlington High School in 1954. As
an undergraduate the author attended Ohio State University
and the University of Florida. In January, 1959, he received
the B.S. degree from the University of Florida with a group
major in biology, chemistry, and psychology. The M.S.
and Ph.D. degrees were also taken at the University of
Florida in June, 1961, and August, 1963. His area of
gnecialization is physiological psychology.
The author served as Research Assistant at the
University of Florida from 1959 to 1961 and at Vanderbilt
University in the summer of 1961. In 1961-1963, he was
supported by the National Institute of Mental Health as
a Research Follow. The author is married to the former
Norma Lee IIiginson of Jacksonville, Florida.
This dissertation was prepared under the direction
of the chairman of the canditato's supervisory committee
and has been approved by all members of that committee.
It was submitted to the Dean of the College of Arts and
Sciences and to the Graduate Council, and was approved
as partial fulfillment of the requirements for the
degree of Doctor of Philosophy.
August 10, 1963.
Dean, College of Arts and Sciencs
Dean, Graduate School