|UFDC Home||myUFDC Home | Help|
This item has the following downloads:
PROCEDURAL LEARNING AND COGNITIVE FLEXIBILITY
IN A MOUSE MODEL OF RESTRICTED, REPETITIVE BEHAVIOR
IN NEURODEVELOPMENTAL DISORDERS
A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
UNIVERSITY OF FLORIDA
To my parents, Nobuo and Reiko Tanimura,
and to my sister, Chie Sato, whose help and support made it possible for me
to pursue a career in science.
I would like to express my sincere thanks to my adviser, Dr. Mark H. Lewis, for the
dedicated guidance and continuous help throughout my thesis work. I would also like to thank
my committee members, Dr. Darragh Devine and Dr. Timothy Vollmer, for their contributions. I
acknowledge and thank Ms. Bonnie I. McLaurin, our laboratory manager, for all the help
throughout the course of my work with animals, and Dr. Mark Yang for the help with analyzing
the data collected for the thesis.
Finally I would like to thank my friends in Gainesville, especially the ladies in the
Behavioral Neuroscience program, as well as those in Japan for encouraging me to finish this
work and to continue pursuing a career in science.
TABLE OF CONTENTS
A CK N O W LED G M EN T S ................................................................. ........... ............. .....
L IST O F T A B L E S ...................................................................................................... . 7
LIST OF FIGURES ................................. .. ..... ..... ................. .8
A B S T R A C T ................................ .................. .......................... ................ .. 9
1 INTRODUCTION ............... ................. ........... ......................... .... 11
Restricted, Repetitive Behaviors in Neurodevelopmental Disorders .................................. 11
Animal Models of Restricted, Repetitive Behaviors......... ..............................12
Stereotypy Associated with Central Nervous System Insults ......................................12
Pharmacologically Induced Stereotypy ................ ... ...............................14
Stereotypy Associated with Environmental Restriction......................................14
Deer M house M odel of Repetitive Behaviors ........... ....... ............................ ............. 16
Effects of Environmental Enrichm ent ..................... ...... ........................ ............... 17
Cortico-Basal Ganglia Circuitry and Repetitive Behaviors........................................18
Cortico-Basal G anglia Circuitry and Cognition ........................................ .....................21
Cortico-Basal Ganglia Circuitry and Cognitive Flexibility................ ...............23
Cortico-Basal Ganglia Circuitry and Environmental Enrichment............... ...................25
A im .................................................................................................. 2 7
2 M A TER IA L S A N D M ETH O D S ........................................ .............................................28
Subj ects ................ .... ................................. ............... 28
Housing Conditions ......................... ....... ... .. ... .. .. ............ .... 28
Stereotypy Assessment .............. ...... ............................. 29
A pparatu s ............... .... .. .......................... ..................................30
P retest A ssessm ent............................. ........................................................... ............... 30
Cognitive Assessment.......... ................. .. .. ... ....................3 1
Procedural Learning ....................... ......................... ...... ........... .... 31
R ev ersal L earn in g ......... ...... .................................. .................................. .... ...... .. 32
D ata A n a ly sis .................................................................................................................... 3 4
3 R E SU L T S .............. ... ................................................................35
Stereotypy A ssessm ent ........................................................................................... ............. 35
C o g n itiv e A sse ssm en t ..................................... .. .. ......................................... ............... 3 6
Effects of Housing Conditions: Enriched vs. Standard Caging ........................ ........36
Procedural Learning .................................. .. .. ......... .. .............36
Reversal Learning....................................................... 38
E effects of Stereotypy L evels.......................................................................... ................... 39
Procedural Learning ................................................ .. ........... .... ....... 39
R eversal Learning................................................... 41
4 D IS C U S S IO N ....... ............................................................................ 5 8
Effects of Housing Conditions on Stereotypy ............................................. ............... 59
Effects of Housing Conditions on Procedural Learning............... ....................................59
Effects of Housing Conditions on Reversal Learning ....................................... ...............61
Effects of Stereotypy Levels on Procedural Learning................................. ...... ...............62
Effects of Stereotypy Levels on Reversal Learning .................................... ............... 63
Modeling a Wider Range of Restricted, Repetitive Behaviors .................. ..................66
L IST O F R E FE R E N C E S ......... .. ................... ........................................................................68
B IO G R A PH IC A L SK E T C H .............................................................................. .....................80
LIST OF TABLES
3-1 The frequency of repetitive vertical jumps and the number of deer mice in four
stereotype groups. ...........................................................................36
LIST OF FIGURES
2-1 Representative swimming paths and responses................................. ............ 33
3-1 Effects of environmental enrichment on stereotypy (vertical jumping and backward
som ersaulting) ............................................................... ..... ..... ......... 44
3-2 Average stereotypy scores in four stereotypy groups.......................................................44
3-3 Latency to reach the platform. A) Effects of housing conditions. B) Effects of
stereotype levels ...................................................... .................. 45
3-4 Distance traveled. A) Effects of housing conditions. B) Effects of stereotypy levels.......46
3-5 Velocity. A) Effects of housing conditions. B) Effects of stereotypy levels.....................47
3-6 The number of first correct arm entries. A) Effects of housing conditions. B) Effects
of stereotype levels. ...................................................... ................. 48
3-7 The number of correct responses. A) Effects of housing conditions. B) Effects of
stereotype levels ...................................................... .................. 49
3-8 The number of error responses. A) Effects of housing conditions. B) Effects of
stereotype levels ...................................................... ................. 50
3-9 The total number of error responses made in the procedural and reversal phases. A)
Effect of housing conditions. B) Effect of stereotypy levels.............. .. ............. 51
3-10 The proportion of error responses made in the procedural and reversal phase. A)
Effects of housing conditions. B) Effects of stereotypy levels ............... ............... 52
3-11 Probability of making a correct response in the first 24 trials of the reversal phase. A)
Effects of housing conditions. B). Effects of stereotypy levels ...................................53
3-12 Probability of making an error response in the first 24 trials of the reversal phase. A)
Effects of housing conditions. B) Effects of stereotypy levels ............... ............... 54
3-13 Regression of the total number of error responses in the reversal phase by individual
stereotype score. ...........................................................................55
3-14 Days required to reach the criterion. A) Effects of housing conditions. B) Effects of
stereotype levels ...................................................... ................. 56
3-15 Effects of housing conditions on trials to the criterion. A) Trials to the procedural
criterion. B) Trials to the reversal criterion. ........................................... ............... 57
Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science
PROCEDURAL LEARNING AND COGNITIVE FLEXIBILITY
IN A MOUSE MODEL OF RESTRICTED, REPETITIVE BEHAVIOR
IN NEURODEVELOPMENTAL DISORDERS
Chair: Mark H. Lewis
Major Department: Psychology
Restricted, repetitive behaviors (e.g., stereotypes, compulsions, rituals) in
neurodevelopmental disorders have been linked to alterations in cortical-basal ganglia circuitry.
Restricted, repetitive behavior has been shown to be associated specifically with deficits in
cognitive flexibility. Cognitive processes mediated by this circuitry (e.g., procedural learning,
executive function) are likely to be impaired in individuals exhibiting high rates of repetitive
To test this hypothesis, we assessed both procedural learning and cognitive flexibility
(reversal learning) using a T-maze task in deer mice exhibiting various rates of repetitive
behavior (vertical jumping and backward somersaulting). These mice exhibited high rates of
stereotypy when reared in standard rodent cages, and such behavior was significantly prevented
by housing them in larger more complex environments.
The results showed that mice reared in complex environments exhibited significantly better
procedural and reversal learning than standard caged mice. Thus, early experience associated
with the prevention and attenuation of stereotypy was associated with better striatally mediated
learning and cognitive flexibility. In addition, mice exhibiting high rates of stereotypy (especially
backward somersaulting) performed most poorly in the reversal phase. The results indicate that
the expression of repetitive motor behavior is associated with perseverative behavior in a
learning and memory task. Our finding enhances the applicability of the deer mouse model of
spontaneous stereotypy to the wide range of restricted, repetitive behavior (e.g., rituals,
insistence on sameness) typical of neurodevelopmental disorders.
Restricted, Repetitive Behaviors in Neurodevelopmental Disorders
Restricted, repetitive behaviors encompass a range of abnormal behaviors, which are
common behavioral phenotypes of several neurodevelopmental disorders. In autism, repetitive
behaviors are expressed as motor stereotypes, repetitive manipulation of objects, and echolalia
as well as more complex behaviors such as compulsions, rituals, insistence on sameness, and
narrow and circumscribed interests (Bodfish et al., 2000; Lewis & Bodfish, 1998; Turner, 1999).
This wide range of repetitive behaviors is also typical of individuals with more severe forms of
mental retardation (Bodfish et al., 2000; Lewis & Baumeister, 1982).
Not surprisingly, motor stereotypes, or simple repetitive, often rhythmic motor
movements (e.g., hand flipping, body rocking), appear relatively early in development. More
complex repetitive behaviors (e.g., complex motor sequences and repetitive use of words)
emerge gradually with age (Militerni et al., 2002; Mooney et al., 2006). Complex repetitive
behaviors seem to involve cognitive as well as motor components, which are often accompanied
by some set of rules or a 'just right' criterion for completion (e.g., rituals and object
attachments). This cognitive rigidity may be a component of a broader profile of deficits in
executive function, which has been widely reported in individuals with autism (Pennington &
Ozonoff, 1996). The association between executive function, particularly cognitive flexibility,
and repetitive behaviors is now being investigated (Lopez et al., 2005).
Although a wide range of restricted, repetitive behavior is characteristic of
neurodevelopmental disorders, specific repetitive behaviors are the typical behavioral
phenotypes of certain genetic disorders. Two examples include repetitive self-biting of lips or
digits in Lesch-Nyhan disease (Cauwels & Martens, 2005) and skin picking in Prader-Willi
syndrome (Symons et al., 1999). Other psychiatric and neurological disorders may also be
associated with specific forms of repetitive behaviors. Two obvious examples include childhood
onset obsessive-compulsive disorder (OCD) (repetitive checking or washing) and Tourette
syndrome (vocal tics) (Cath et al., 2001; Muller et al., 1997).
In general, restricted, repetitive behaviors are considered abnormal and clinically
significant because they are stigmatizing, preclude or disrupt goal-directed actions, limit
interaction with the environment, and on occasion, are self-injurious. The pathophysiology of
these behaviors has received limited clinical study, although several neuroimaging and
pharmacological challenge studies have been published (Hollander et al., 2005; Malone et al.,
2005). A more complete understanding of neurobiological perturbations responsible for
repetitive behavior disorders would greatly facilitate the development of treatment options for
patients. Such an understanding will require use of valid animal models.
Animal Models of Restricted, Repetitive Behaviors
To study the underlying neurobiological basis of repetitive behaviors, several categories of
relevant animal models are available. These categories include stereotypy associated with central
nervous system (CNS) insults, pharmacologically induced stereotypy, and stereotypy induced by
rearing animals in restricted environments (Lewis et al., 2006). Although these models should
ideally reflect the wide range of repetitive behaviors displayed in individuals with
neurodevelopmental disorders, they tend to focus largely on motor stereotypy. This is because
stereotypy is observed relatively easily, whereas it is much more challenging to assess more
complex behavior that may be considered models of rituals or insistence on sameness in animals.
Stereotypy Associated with Central Nervous System Insults
Recent advances in genomics, particularly the ability to knock out specific genes, have
provided important information about the etiology of neuropsychiatric disorders. Of particular
interest is that some of these gene-manipulated animals demonstrate repetitive behaviors, which
resemble the repetitive behavior symptoms in clinical populations.
For example, a loss of function mutation in the methyl-CpG binding protein 2 (MeCP2)
gene is known as a major cause of Rett syndrome, and MeCP2 abnormalities are also reported in
individuals with mental retardation and autism (Carney et al., 2003; Meloni et al., 2000).
Compared to control animals, mice expressing truncated MeCP2 protein display more repetitive
forepaw movements, which resemble hand stereotypes (hand wringing and waving) commonly
engaged in by patients with Rett syndrome (Moretti et al., 2005; Shahbazian et al., 2002).
Excessive grooming resulting in hair removal and tissue damage has been reported in
Hoxb8 homozygous knockout mice (Greer & Capecchi, 2002). Expression of the Hoxb8 gene is
found in the orbitofrontal and anterior cingulate cortices, and caudate nucleus, which are the
brain regions comprising 'OCD circuitry' (Graybiel & Rauch, 2000). Excessive grooming in
Hoxb8 knockout mice has particular resemblance to trichotillomania, an OC spectrum disorder.
Similarly, a significantly increased number of brief head or body jerks is found in D1CT-7
transgenic mice expressing a neuropotentiating transgene in cortico-limbic glutamatergic
neurons, which seems to be overactivated in patients with OCD and Tourette's syndrome
(Nordstrom & Burton, 2002). Such behavior is suppressed by clonidine, an alpha-2 adrenergic
agonist that is commonly used to reduce tics in clinical population.
In addition to CNS insults via gene manipulations, prenatal exposure to environmental risk
factors has been shown to induce similar behavioral phenotypes to those seen in patients with
neurodevelopmental disorders. Prenatal exposure to valproic acid (VPA) has been advanced as a
potential etiological factor for autistic symptoms (Folstein & Rosen-Sheidley, 2001; Keller &
Persico, 2003). Exposure of this antiepileptic drug to rats on day 12.5 of gestation produced
neuropathological abnormalities similar to those reported in autistic individuals (e.g., altered
sensitivities to tactile stimuli, diminished prepulse inhibition, decreased social behaviors, and
hyperactivity including stereotypy-like behaviors) (Schneider & Przewlocki, 2005).
Pharmacologically Induced Stereotypy
Much of what we know about the neurobiological basis of motor stereotypy comes from
investigations using pharmacological models (Lewis & Baumeister, 1982; Lewis & Bodfish,
1998). These models have a direct human analogue, as clinically abnormal repetitive behaviors
were described in human amphetamine abusers as early as the late 1960s (Ellinwood, 1967;
Kramer et al., 1967). Such phenomena were also demonstrated in several species of animals
treated with amphetamine (Randrup & Munkvad, 1965). Subsequently, a wide range of other
pharmacological agents (e.g., phenmetrazine, L-dopa, morphine, methylphenidate, pemoline, and
monoamine oxidase inhibitors) that affect the nigro-striatal dopaminergic system was shown to
induce stereotypy in rats (Fog, 1972).
Systematic investigation of anatomical and neurochemical mechanisms underlying drug-
induced repetitive behavior implicated cortico-basal ganglia circuitry in the execution of these
movements. Intrastriatal and systemic administration of direct and indirect dopamine agonists
(e.g., amphetamine, apomorphine, and cocaine) as well as opiate agonists and NMDA receptor
antagonists (e.g., MK-801 and PCP) have consistently induced motor stereotypy (Ernst &
Smelik, 1966; Iwamoto & Way, 1977; Lewis et al., 1990; Segal et al., 1995; Vandebroek et al.,
1998; Vandebroek & Odberg, 1997). Cortico-basal ganglia circuitry will be discussed more in
detail in a later section.
Stereotypy Associated with Environmental Restriction
Repetitive motor behaviors not requiring pharmacological induction are frequently
reported in animals housed in zoo, farm, and laboratory environments (Mason, 1991). Examples
of these species-specific stereotypic behaviors include pacing, route-tracing, and feather-picking
in parrots and tits (Garner et al., 2003a; Garner et al., 2003b; Jenkins, 2001; Meehan et al.,
2004), bar-mouthing, vertical jumping, and backward somersaulting in rodents (Garner &
Mason, 2002; Powell et al., 1999; Vandebroek & Odberg, 1997), pacing, body-rocking, tail-
biting, and self-injurious behavior in rhesus monkeys (Lutz et al., 2003; Taylor et al., 2005),
pacing, somersaulting, and over-grooming in prosimians (Tarou et al., 2005), crib-biting,
boxwalking, and head-shaking in horses (Bachmann et al., 2003; McGreevy et al., 1995),
regurgitation and tongue flicking in pandas (Swaisgood et al., 2005), and head-twirling in minks
Since animals in the wild do not engage in such abnormal behaviors, stereotypy seems to
develop as a consequence of animals' responses to restricted environments, which limit
expression of species-typical behaviors. Conversely, alleviation of environmental deprivation
seems an effective means to reduce rates of spontaneous stereotypy (Garner et al., 2003a;
Meehan et al., 2004; Powell et al., 2000; Swaisgood et al., 2005; Turner et al., 2002).
Importantly, motor stereotypy associated with restricted environments has been
demonstrated to be qualitatively different from pharmacologically induced stereotypy in the
same species. For example, deer mice develop focused vertical jumping and backward
somersaulting as a consequence of restricted housing, whereas they exhibited excessive gnawing,
rearing, and locomotion following administration of apomorphine (Presti et al., 2004; Presti et
al., 2002). Similarly, although repetitive jumping is commonly displayed in captive bank voles,
NMDA receptor antagonist MK-801 and apomorphine elevated repetitive licking, sniffing, and
locomotion instead (Vandebroek et al., 1998; Vandebroek & Odberg, 1997). These findings
suggest the limitations of drug-induced stereotypy to model repetitive behavioral phenotypes of
Motor abnormalities associated with environmental restriction are strikingly similar to the
phenomena (spontaneous, repetitive, topologically unvarying, functionless, and apparently
purposeless) in neurodevelopmental disorders. These individuals are likely to experience
environmental restriction early in life as a function of their handicap. Thus, it is possible that
similar neurodevelopmental perturbations spontaneously occur in stereotypic animals reared in
restricted environments and individuals with neurodevelopmental disorders. Studying the
neurobiological mechanisms of stereotypy using a model associated with environmental
restriction will advance our knowledge of the development of restricted, repetitive behavior
associated with neurodevelopmental disorders. To this end, we have adopted a mouse model of
stereotypy induced by environmental restriction. This model utilizes a species that can be studied
in the laboratory and whose stereotypy is spontaneous, persistent, and occurs early in
Deer Mouse Model of Repetitive Behaviors
In our laboratory, we employ deer mice (Peromyscus maniculatus) as a model of repetitive
behavior disorders. These animals exhibit high rates of repetitive vertical jumping or backward
somersaulting when housed under standard laboratory conditions (Powell et al., 1999). These
behaviors emerge as early as weaning and persist for a prolonged period of time. Exposure to a
larger, more complex environment (environmental enrichment or EE) following weaning
significantly attenuates the development of these behaviors (Powell et al., 2000). After two
months of EE following weaning, approximately 80 percent of mice show low rates of
stereotyped behaviors, whereas close to 80 percent of mice reared in standard cages (SC) show
high rates of stereotyped behavior. Enrichment later in life is also beneficial, yet to a lesser
degree (Hadley et al., 2006; Powell et al., 2000).
Effects of Environmental Enrichment
The significance of environmental stimulation on behavior was first recognized through
the pioneering work of Hebb (1949). He reported that rats he brought home from his laboratory
to keep as pets were better at solving cognitive tasks than rats raised in the laboratory. Since this
early observation, EE has been used to demonstrate behavioral and brain plasticity in a large
number of studies using a variety of behavioral and biological measures or endpoints (Lewis,
2004; van Praag et al., 2000). It should be noted, however, that EE is a relative term and that
such experimental configurations cannot approximate the complexity and variability of the
animal's natural habitat.
EE may also have beneficial effects in preventing or attenuating the effects of CNS insult.
A higher educational background, cognitively challenging occupations, and high socioeconomic
status were found to lower the risk of Alzheimer's disease and cognitive impairment associated
with age (Moceri et al., 2001; Snowdon et al., 1996; Stern et al., 1994; White et al., 1994). In a
transgenic mouse model of Alzheimer's disease, EE prevented overproduction of amyloid-beta
protein and learning impairments associated with amyloid deposits (Jankowsky et al., 2005).
Furthermore, the neuroprotective role of EE was found in a 1-methyl-4-phenyl-1,2,3,6-
tetrahydropyridine (MPTP) mouse model of Parkinson's disease (Faherty et al., 2005), where EE
significantly attenuated the death of dopaminergic neurons in the substantial nigra pars compact
(SNpc). As another example, transgenic mice expressing human huntingtin transgene, a mouse
model of Huntington's disease, showed amelioration of motor abnormalities following EE. In
addition, EE rescued molecular alterations caused by transcriptional dysregulation in these mice,
such as reduction in brain derived neurotrophic factor (BDNF) in the hippocampus and striatum,
and dopamine and cAMP-regulated phosphoprotein 32 kDa (DARPP-32) deficits in the anterior
cortex (Spires et al., 2004).
Of particular interest are behavioral modifications in animal models of
neurodevelopmental disorders associated with repetitive behavior. A recent study showed that
mice with fragile X mental retardation 1 gene mutation, an animal model of Fragile X syndrome,
displayed hyperactivity, cognitive alterations, and immature dendritic and spine morphology
when housed in standard rodent cages, whereas enriched experiences normalized mutation-
associated cognitive and morphological impairments (Restivo et al., 2005). Similarly, VPA-
treated rats, modeling autism, exhibited stereotypy-like behaviors under standard laboratory
conditions, whereas VPA rats under EE conditions alleviated repetitive behaviors as well as
other parameters characteristic of autism (Schneider et al., 2006).
As suggested previously, our lab has demonstrated that EE markedly attenuates the
development of spontaneous stereotypy in deer mice. We have also examined the
neurobiological correlates of this experientially based attenuation. Specifically we found
elevated metabolic activity and dendritic spine density in the motor cortex and dorsolateral
striatum in EE mice exhibiting diminished levels of stereotypy (Turner et al., 2003; Turner et al.,
2002). Moreover, BDNF in the striatum was elevated in these enriched low-stereotypy mice
(Turner & Lewis, 2003). Thus, it is reasonable to hypothesize that altered activity within this
circuitry is responsible for the expression of repetitive behavior in deer mice.
Cortico-Basal Ganglia Circuitry and Repetitive Behaviors
The basal ganglia are a group of subcortical nuclei that regulate execution of motor and
cognitive programs. They receive inputs from all areas of the neocortex except the primary
visual and primary auditory cortices. The motor circuit that is hypothesized to be responsible for
the expression of stereotypy originates from the primary motor cortex and premotor area.
Glutamatergic neurons from these cortical regions enter the input nucleus of the basal ganglia
(dorsolateral striatum) and the output neurons from the basal ganglia regulate activation of
thalamocortical neurons. These neurons terminate at the somatosensory cortex, primary motor
cortex, and supplementary motor area, providing positive feedback to ongoing motor programs
in the primary motor cortex (Herrero et al., 2002; Parent & Hazrati, 1995).
There are two pathways that travel through the basal ganglia system: the direct pathway
and indirect pathway. The direct pathway consists of GABAergic medium spiny neurons directly
projecting from the dorsolateral striatum to the output nucleus of the basal ganglia, the globus
pallidus internal (GPi) and substantial nigra pars reticulata (SNpr) (striatonigral neurons). These
neurons selectively express D1 dopamine receptors that are co-localized with glutamate
receptors. They contain the neuropeptides dynorphin and substance P (Steiner & Gerfen, 1998).
The indirect pathway consists of GABAergic striatal medium spiny neurons (striatopallidal
neurons) projecting to the globus pallidus external (GPe), GABAergic neurons in the GPe
projecting to the subthalamic nucleus (STN), and finally glutamatergic neurons sending
excitatory projection to the GPi and SNpr. The striatopallidal medium spiny neurons express D2
receptors, and the neuropeptide enkephalin (Steiner & Gerfen, 1998).
Normal dopaminergic innervation in the striatum plays a crucial role in execution of
movements. D1 receptors in the striatonigral neurons are positively coupled to adenylyl cyclase
(Missale et al., 1998). Therefore, dopamine acts to amplify the glutamatergic corticostriatal
inputs, resulting in increased GABAergic inhibition of the GPi and SNpr. In contrast, D2
receptors in the striatopallidal neurons are negatively coupled to adenylyl cyclase (Missale et al.,
1998). Via D2 receptors, dopamine acts to diminish the corticostriatal inputs, resulting in
decreased inhibition of the GPe, hence causing this nucleus to exert even more inhibitory control
over the STN. This increased inhibition of the STN removes its excitatory influence on the GPi
and SNpr. Thus activation of D1 and D2 receptors both removes inhibitory tone of the basal
ganglia output neurons, ultimately resulting in disinhibition of the thalamocortical neurons to
provide positive feedback to motor programs.
Abnormal execution of movements is evident when the balance between the direct and
indirect pathway is disrupted. It is postulated that stereotypic behavior is expressed as a
consequence of a relative increase in striatonigral tone (Graybiel et al., 2000). This hypothesis is
supported by the finding that transgenic mice inducibly overexpressing the transcription factor
AFosB selectively in dynorphin-containing striatonigral neurons exhibit increased daily wheel
running, whereas such behavior was significantly reduced in mice overexpressing AFosB in
enkephalin-containing striatopallidal neurons (Werme et al., 2002).
To investigate alterations in cortico-basal ganglia circuitry in deer mice exhibiting
spontaneous stereotypy, we administered the selective D1 antagonist SCH23390 and the NMDA
antagonist MK-801 intrastriatally. These compounds both blocked spontaneous stereotypy
selectively (Presti et al., 2003). In contrast, the D2 receptor antagonist raclopride, unexpectedly
failed to reduce stereotypy (Presti et al., 2004). Finally, the mixed agonist apomorphine failed to
increase spontaneous stereotypes in deer mice when administered intrastriatally (Presti et al.,
In addition, we assessed neuronal activities of the direct and indirect pathways by
measuring neuropeptides dynorphin and enkephalin respectively. We found significantly
decreased leu-enkephalin content and significantly increased [dynorphin]/[enkephalin] content
ratios in high-stereotypy mice relative to low-stereotypy mice. Moreover, we saw a significant
negative correlation between striatal enkephalin content and frequency of stereotypy as well as a
significant positive correlation between the [dynorphin]/[enkephalin] content ratio and frequency
of stereotypy in these mice (Presti & Lewis, 2005).
Another line of evidence for potential neurobiological perturbations responsible for
repetitive behaviors comes from neuroimaging studies in clinical populations exhibiting
behaviors of interest. Increased right caudate volume was noted in individuals with autism
spectrum disorders, which was positively correlated with rates of repetitive behaviors, especially
scores of higher-order components (Hollander et al., 2005), such as compulsions, rituals, and
difficulties with minor change, and complex motor mannerisms (Sears et al., 1999). Patients with
trichotillomania displaying repetitive hair-pulling had significantly reduced volumes of the left
putamen (O'Sullivan et al., 1997). Moreover, tics in Tourette syndrome were inversely correlated
with changes of blood flow and oxygen concentration in the basal ganglia and thalamus
(Peterson et al., 1998).
These studies provide evidence for alterations of cortico-basal ganglia circuitry in animals
and individuals associated with repetitive behaviors. To further support alterations in this
circuitry in stereotypic animals, we wished to assess other non-stereotyped behaviors, which
require the intact basal ganglia system for normal function. We focused on cognitive behaviors
including striatally mediated procedural learning and cognitive flexibility, which require intact
fronto-basal ganglia circuitry.
Cortico-Basal Ganglia Circuitry and Cognition
The role of the striatum in mnemonic function, which is distinct from the hippocampally
dependent system, is increasingly appreciated. A number of studies demonstrated double
dissociation of two memory systems; the hippocampus mediates spatial, allocentric memory,
which relies on stimulus-stimulus relationships or Tolmanian cognitive mapping strategy,
whereas the striatum plays an important role in motor, egocentric memory, which in particular
emphasizes acquisition of Hullian stimulus-response (S-R) relationships (Packard & Knowlton,
2002; White & McDonald, 2002; Yin & Knowlton, 2006).
This dissociation of relatively independent memory systems is supported by the findings
that localized lesions of fimbria-fornix, a major input-output pathway of the hippocampus,
impaired spatial memory, whereas caudate lesions were associated with poor performance in
discrimination learning tasks, using spatial and cue versions of Morris water maze tasks
(McDonald & White, 1994; Packard & McGaugh, 1992) or win-shift and win-stay radial-arm
maze tasks (Kesner et al., 1993; Packard & White, 1991) respectively.
Different biochemical processing associated with these systems also provides evidence for
the mnemonic dissociation. For example, calcium-sensitive adenylyl cyclase activity was
increased to the greatest degree in the hippocampus after spatial learning, whereas calcium-
insensitive adenylyl cyclase was enhanced in several areas of the brain, especially the striatum,
following procedural learning (Guillou et al., 1999).
Furthermore, immediately after maze training that assessed either place or response
learning, both phosphorylated CREB (pCREB) and c-fos expression were increased in either
group of animals, which experienced place or response learning. After one hour, sustained
pCREB and c-fos immunoreactivity was observed in the hippocampus (the dentate gyms, CA1,
and CA3) following place learning, whereas pCREB activity was sustained in the striatum
(dorsolateral and dorsomedial) following response learning (Colombo et al., 2003). CREB is
widely known to contribute to memory consolidation and dynamic modulation of synaptic
strength. Thus, task acquisition seems to require initial activation of multiple brain regions, but
the region responsible for acquisition of the task later undergoes greater activation to consolidate
the learned strategy. Additionally, CREB mutation impaired performance in several tasks
associated with the dorsal striatum and altered corticostriatal long-term potentiation (LTP) and
depression (LTD) (Pittenger et al., 2006), supporting the involvement of this subcortical area in
learning, which is distinct from the hippocampally mediated learning.
This change in neural activation with learning is also supported electrophysiologically.
Graybiel and colleagues (Barnes et al., 2005; Jog et al., 1999) demonstrated that many of
dorsolateral striatal neurons were activated shortly after a discriminative auditory stimulus,
which indexed the location of a reward, in the simple discrimination T-maze task at the
beginning of training. However, as rats learned the S-R contingency, the neuronal firings at the
beginning (trial start) and end (reward) of the maze were enhanced and the firings at the tone and
turn were substantially attenuated. This shift in neuronal firings associated with procedural
learning was largely reversed during extinction learning.
In humans, functional magnetic resonance imaging (fMRI) studies provided evidence for
the involvement of the striatum in probabilistic classification task, which requires non-motor
procedural memory (Poldrack et al., 1999). Patients with the basal ganglia pathology, such as
Huntington's (Knopman & Nissen, 1991; Sprengelmeyer et al., 1995) and Parkinson's diseases
(Allain et al., 1995; Krebs et al., 2001), present a variety of cognitive impairments attributable to
the striatal memory system. Although some evidence exists (Mostofsky et al., 2000), not much is
known regarding S-R learning deficits in individuals with neurodevelopmental disorders who
exhibit restricted, repetitive behaviors.
Cortico-Basal Ganglia Circuitry and Cognitive Flexibility
Other domains of cognitive function, which require intact cortico-basal ganglia circuitry,
include executive function. Executive function is an umbrella term for cognitive processes such
as attention, planning, working memory, and cognitive flexibility, which require higher-order
mental acts. The disturbances of these processes are reported in many psychiatric disorders such
as schizophrenia and autism (Pennington & Ozonoff, 1996). According to recent human and
animal studies, these processes are largely mediated by the frontal cortex, which has strong
connections with the striatum in series of fronto-striatal loops (Dalley et al., 2004; Heyder et al.,
Of most interest to us among these subcomponents of executive function is cognitive
flexibility. Damage in subregions of the frontal cortex (dorsolateral prefrontal cortex and
orbitofrontal cortex) causes a difficulty in shifting a response or switching strategies when S-R
contingency changes. Thus, patients with frontal damage often repetitively respond to the
previously relevant, however no longer associated, stimuli. This perseverative behavior pattern
resembles simple motor stereotyped behaviors where both are inappropriately repeated and rigid
(Lewis & Bodfish, 1998). Hence, perturbations within the striatum could dysregulate not only
cortical-striatal loop inducing repetitive motor behavior, but also fronto-striatal loops impairing
To support this hypothesis, recent investigations presented evidence for the link between
stereotypy associated with restricted environment and cognitive rigidity. For example, blue and
marsh tits exhibiting repetitive route-tracing stereotypy showed a perseverative response pattern
in a gambling task (Garner et al., 2003a; Garner et al., 2003b), which has been used for cognitive
assessment in schizophrenia (Frith & Done, 1983) and OCD (Cavallaro et al., 2003). In this task,
subjects are instructed to search for the rule governing the reward presentation contingent on a
particular stimulus, when in fact there is no rule. Therefore their sequences of responses reveal
repetition of a specific response or repetitive pattern of responses.
A similar correlation was also found between cage stereotypes and reversal (where the
reinforcer was switched and associated to the opposing stimulus) or extinction (where the
reinforcer no longer existed) of S-R learning in bank voles (Garner & Mason, 2002; Garner et
al., 2003a) and bears (Vickery & Mason, 2005). Moreover, this relationship was recently
demonstrated by Lopez and colleagues (2005) in clinical populations. Scores on the executive
function task that indexed cognitive rigidity were positively correlated with severity of restricted,
repetitive behavior in autistic adults. This relationship between motor and perseverative
responses in the California Trail Making Test is of interest to many researchers, because
executive function deficits have been recognized in autistic individuals relatively independently
of repetitive motor behavior. Therefore, we wished to demonstrate such an association between
stereotypy and cognitive flexibility in our deer mice model.
Cortico-Basal Ganglia Circuitry and Environmental Enrichment
Evidence consistently supports that exposure to EE improves performance in various
cognitive tasks, which are at least partially dependent on the hippocampus (e.g., go/no go task,
object recognition task, contextual fear conditioning, spatial version of Morris water maze, and
open field test) (Duffy et al., 2001; Lambert et al., 2005; Leggio et al., 2005; Park et al., 1992;
Pham et al., 1999; Woodcock & Richardson, 2000).
EE has also been shown to attenuate impaired learning systems associated with
hippocampal (Will et al., 1983) and fimbria-fornix lesions (van Rijzingen et al., 1997),
immunolesioned basal forebrain cholinergic system (Paban et al., 2005), mutation in CA1-
specific NMDA receptor 1 subunit (Rampon et al., 2000), traumatic brain injury (Dahlqvist et
al., 2004; Gobbo & O'Mara, 2004; Rutten et al., 2002; Wagner et al., 2002), high fat diet
(Winocur & Greenwood, 1999), and age (Frick & Fernandez, 2003; Frick et al., 2003).
Biochemical indices of neural plasticity associated with learning improvement include increased
levels of neurotrophic factors (Pham et al., 1999), alteration of the cAMP-dependent protein
kinase dependence of LTP (Duffy et al., 2001), and increased phosphorylation of CREB
(Williams et al., 2001; Young et al., 1999) in the hippocampus.
Moreover, adult neurogenesis in the hippocampus is enhanced following EE. Bruel-
Jungerman and colleagues (2005) demonstrated that these new neurons actually contribute to
hippocampally mediated memory improvement associated with EE. Mice were housed either
under EE or standard laboratory conditions, and half of EE mice were treated with saline and the
other half were treated with antimitotic methylazoxymethanol acetate (MAM), which prevented
further cell division. There was significant elevation in 5-bromo-2'-deoxyuridine (BrdU)-
positive new born cells in EE naive mice compared to EE MAM mice and mice from standard
cages, implicating EE-dependent increase in neurogenesis in the dentate gyrus. Moreover, EE
naive mice showed statistically better long-term recognition memory than EE MAM-treated
mice, providing the first direct evidence for adult neurogenesis in the hippocampus following EE
and their functional participation in memory enhancement.
Thus, the role of EE on hippocampally mediated learning and memory has been
extensively studied behaviorally and neurobiologically. Fewer attempts to understand the
efficacy of EE on striatum-mediated learning have been made (Frick & Fernandez, 2003; Frick
et al., 2003; Schrijver & Wurbel, 2001). Frick and Fernandez (2003) demonstrated that age-
related memory impairment was rescued following EE in the spatial version of Morris water
maze, but not in the cued version of Morris water maze, which assesses procedural learning. An
increase in synaptophysin was evident in the hippocampus and frontoparietal cortex in EE mice,
but no such assessment was done for the striatum. Similarly, other studies failed to show
procedural learning enhancement following exposure to EE. Therefore, we wish to evaluate
carefully EE effect on striatum-mediated procedural learning in deer mice.
Conversely, studies support the effect of EE on cognitive flexibility. Isolation housing
impaired reversal learning (Jones et al., 1991; Schrijver et al., 2004) and extradimensional set-
shifting (Schrijver & Wurbel, 2001), isolated animals showing more perseverative responses
than their socially reared counterparts. Yet, effects of other EE components (e.g., cognitive
stimulation and exercise) and the neurobiological alterations associated with cognitive rigidity
have not been studied. Thus we wished to assess the effect of EE on cognitive flexibility in deer
Restricted, repetitive behaviors are clinically significant for several neurodevelopmental
disorders. Studies using pharmacologically induced animal models of stereotypy as well as our
deer mice model associated with restricted environment suggest that the relatively increased tone
of the direct pathway compared to the indirect pathway is responsible for the expression of
repetitive behaviors. To further confirm the alteration in the basal ganglia system in animals
displaying high rates of stereotypy, we hypothesized that other non-stereotypy behaviors
mediated by this brain region, such as procedural learning and cognitive flexibility, are also
impaired in these animals. To investigate these hypotheses, the present experiment examined the
relationship between spontaneously emitted stereotypy and these cognitive processes as well as
effects of EE on them using the water-filled T-maze.
MATERIALS AND METHODS
As we have previously demonstrated, both male and female Peromyscus maniculatus (deer
mice) develop high rates of persistent, spontaneously emitted stereotypy consisting of repetitive
vertical jumping and backward somersaulting when housed under standard laboratory conditions.
In most mice, these behaviors can be markedly attenuated by environmental enrichment. Fifty-
nine mice were originally designated for this experiment, but during the period from weaning to
the completion of the reversal phase, four mice died for unknown reasons and three mice were
excluded. Data from 52 mice (23 male and 29 female; 3-7 months old) were used for analysis.
Subjects were obtained from the breeding colony maintained in our laboratory, and at weaning
were randomly assigned to either standard cage (SC) or enriched environment (EE) housing
Rodent chow and water were available ad libitum, and Cockatiel vita seed was provided
three times each week. The housing room was maintained at 20-250C and 50-70 % humidity.
Subjects were maintained on a 16:8-h light/dark cycle, with lights off at 10:00pm. All procedures
were performed in accordance with the guidelines set forth in the NIH Guide for the Care and
Use of Laboratory Animals and were approved by the University of Florida Institutional Animal
Care and Use Committee.
Mice assigned to EE were group-caged (6 same sex mice/cage) in large dog kennels (122 x
81 x 89 cm) consisting of two extra levels constructed of galvanized wire mesh and connected by
ramps of the same material. Bedding, a running wheel, shelters (similar opaque, concave object),
and various other objects (habitrail tubes, plastic toys, and mesh structures for climbing) were
placed in each kennel prior to introducing the mice. One oz. of Cockatiel vita seed was scattered
throughout the kennel three times each week to encourage foraging behavior. A running wheel
remained undisturbed in the kennel, but other objects (except those in which mice were hiding)
were removed and replaced with clean novel objects on a weekly basis.
For the SC condition, mice were caged (2-3 same sex mice/cage) in standard laboratory
rodent cages (48 x 27 x 15 cm). A half oz. of Cockatiel vita seed was placed at one corer of the
cage three times each week on the same schedule as the enriched cages in order to
counterbalance any nutrition effects with the EE mice.
After being housed in their respective caging conditions for 60-180 days, the mice were
tested for rates of stereotyped behavior. Prior to cognitive assessment, mice from both SC and
EE conditions were tested for rates of stereotypy using a modified automated photocell detection
apparatus obtained from Columbus Instruments (Columbus, CO). This equipment uses
photocells located 13.5 cm above the floor, to quantify the number of interruptions made by
repetitive jumps or backward somersaults of a mouse during a given time period.
The session consisted of the eight hours of the dark cycle for two consecutive days. Any
single testing day involved three mice from the EE housing and two or three mice from the SC
housing sharing a common weaning date. The testing protocol involved removing mice from
their home cages and placing them singly in testing cages (22 x 15 x 28 cm) made of Plexiglas
prior to the beginning of the dark cycle. Food and water were provided, and the mice were left
undisturbed for two to three hours for habituation to the new cage and recovery from the stress of
All sessions were digitally video recorded for further identification of behavior phenotypes
and accuracy of the automated counters. Each animal received a stereotypy score that
represented the average stereotypy frequency per hour.
The testing apparatus consisted of a T-maze constructed from clear Plexiglas. Each arm
measured 7.5 x 32 x 18 cm. The platform (7.5 x 7.5 x 5 cm) made of the same Plexiglas material
was placed at the end of one arm. The maze was placed in a black plastic tank (85 cm in
diameter, 36 cm in height) and a white nylon curtain (85 cm in diameter, 60 cm in height)
surrounded the T-maze.
Prior to cognitive testing, the T-maze was filled with warm tap water (25 C) to a depth of
5.8 cm so that the clear platform was submerged 8 mm from the surface of the water. In order to
keep the temperature constant, the water was measured every eight trials and hot tap water was
added as needed. Non-toxic white paint was added to the water to ensure opacity.
A digital video camera was mounted 120 cm above the T-maze to make recordings of
swim trials. The camera was connected to a computer in the same room and used to measure
mice's escape latencies and track swimming paths by Ethovision" video tracking system (Noldus
Information Technology, the Netherlands).
Mice were tested in the visible-platform version of Morris water maze task to detect any
motor or sensory abnormalities. The black tank was filled with warm tap water (25-280C) and the
white plastic platform (10 x 10 cm) was placed in the tank, 5 mm above the surface of water.
Mice were released from the edge of the tank and allowed to swim to the platform for up to 60
seconds. This was repeated four times and the location of the platform and the releasing point
were varied in every trial with an intertrial interval of approximately 15 minutes. During the
intertrial interval, the mice were returned to their cage in an adjoining room, towel dried and
placed underneath a heating lamp. Mice's swimming patterns were analyzed. Those mice
exhibiting apparent motor and sensory impairments were excluded from further cognitive
On the following day, mice were exposed to the T-maze, which was placed in the tank and
filled with warm opaque water without the platform. Mice were released from the start arm
facing to the wall and allowed to explore the T-maze for 30 seconds. This was repeated six times
with intertrial interval of approximately 15 minutes. The swim paths were digitally recorded to
determine the existence of turning bias in each animal. Mice were determined to have a turning
bias, when they made more than five first entries to the same arm.
On the day following T-maze habituation, mice were tested for procedural memory in the
water-filled T-maze with the invisible platform. Each training session consisted of eight trials.
The platform was placed at the end of the east or west arm. The location of the platform was
pseudorandomly determined among mice except for those animals exhibiting a turning bias. For
those cases (n=6), the platform was positioned in the non-preferred arms. Four extra-maze cues
(different color, geometric shapes, approximately 15 x 15 cm in diameter) were attached to the
surrounding nylon curtain and their locations were randomly changed every trial.
A trial began by placing a mouse at the end of the start arm (facing the wall) and ended
when the mouse climbed onto the platform, or after 60 seconds had elapsed. If the mouse did not
escape after 60 seconds, it was gently guided to the platform, placed on the platform, and
removed from the maze. For each mouse there was a delay of approximately 15 minutes between
successive trials within a session. During the delay, the remaining mice were run on the same
trial. Thus, the intertrial interval varied slightly according to the mice's level of performance but
was approximately equal for all mice within each trial.
Completion of a trial was defined as spending two seconds on the platform. If a mouse
reached the platform but jumped out to the water again, the trial was continued until the mouse
reached the platform again and spent two seconds there. Each mouse was left on the platform for
15 seconds and then returned to the home cage, located in an adjoining room.
A correct response was defined as reaching the platform without entry into the opposite
arm (Figure 2-1). An incorrect response was scored when the mouse entered the arm not
containing the platform. When an animal swam all the way to the end (7.5 x 7.5 cm) of the arm
not containing the platform, the trial was recorded as an error response. The criterion for the
procedural phase was set as seven or eight correct responses per session for three consecutive
A reversal-learning task was initiated the day after the animal met criterion for successful
completion of the procedural task. For this task, the same T-maze was employed except that the
platform was placed at the end of the opposite arm (East -* West, West -* East) so that mice
needed to inhibit the previously relevant response and learn the new stimulus-response
association. The criterion for this task was also set as seven or more correct responses for three
Figure 2-1. Representative swimming paths and responses: A response in a single trial was
defined as either a correct, incorrect, or error response. The shaded area at the end of
east arm represents a submerged platform. The corresponding area of the opposite
arm represents the error zone. A) A correct response: completion of a trial without
entry to the incorrect arm. B) An incorrect response: completion of a trial with entry
to the incorrect arm. C) An error response: completion of a trial with entry to the error
zone at the end of the incorrect arm.
A stereotypy score was calculated for each animal and a Student's t test was performed to
determine the effects of differential housing on stereotypy expression (Sigmastat, Systat
Software, CA). Based on the stereotypy score, groups of mice were constituted according to
different rates of stereotypy expression.
An analysis of variance (ANOVA) for repeated measures was performed to determine the
effect of housing condition and stereotypy levels on indices of cognitive performance including
latency, distance traveled, velocity, and the probability of making a correct or error response.
Further post hoc pairwise comparison tests (Tukey) were conducted to assess differences
between stereotypy groups where appropriate. Moreover, a Student's t test for housing condition
and a one-way ANOVA for stereotypy groups were performed for the days required to reach the
criterion. In addition, individual stereotypy scores were regressed against the number of correct
or error responses made. A p-value of .05 or less was adopted for assigning statistical
Stereotypy scores as measured by the automated photocell detection apparatus ranged from
38 to 2394 responses per hour for all animals. There was a significant housing effect on
stereotypy score (t(50)=4.1, p<0.001) with EE mice (n=25) exhibiting significantly lower rates of
stereotypy than SC mice (n=27) (Figure 3-1). When a small number of mice exhibiting backward
somersaulting, all of which were in the SC condition, were excluded from the analysis, a
significant difference in housing conditions was still found (t(41)=4.3, p=0.001).
To group mice according to rates of stereotypy, we first separated mice displaying
repetitive backward somersaulting (B) for the following reasons. First, this qualitatively distinct
behavior takes more time to complete a single response than does a vertical jump. Thus, the
frequency of backward somersaulting is typically less than that observed for vertical jumping.
Second, all of the mice exhibiting backward somersaulting (n=9) were in the SC condition.
Finally as shown in the Cognitive Assessment section below, this group of mice showed distinct
The remaining mice showing vertical jumping were categorized according to whether their
frequency of jumping fell into the upper, middle, or lower third of the frequency range: high (H,
more than 761 counts per hour, n=15), middle (M, between 334 to 760, n=14), and low rate of
jumping (L, less than 334, n=14). The number of mice in each housing condition so categorized
is depicted in Table 3-1. The average stereotypy score per hour for each group is depicted in
Figure 3-2. We were not able to assess the interaction between stereotypy levels and housing
conditions due to the small number of mice in the enriched housing high stereotypy group and
the standard cage low and middle stereotypy group. According to photocell interruption
frequencies obtained for mice exhibiting backward somersaulting, five mice would have been
categorized as high stereotypy and two would have been categorized as middle and low each.
Table 3-1. The frequency of repetitive vertical jumps and the number of deer mice in four
Stereotypy Group Stereotypy Score # of SC Mice # of EE Mice
High rates of jumping 761 < 12 3
Middle rates of jumping 334 760 4 10
Low rates of jumping < 333 2 12
Backward somersaulting (255-1268) 9 0
Since some mice reached criterion on the third day of training for both the procedural
learning and reversal learning experiments, we compared the average trial latencies, distance
traveled, and swim speed as well as the number of first correct arm entries, correct responses,
and error responses within a session for the first three days of the procedural (P1, P2, P3) and
reversal (R1, R2, R3) experiments. Thus, in order to examine the effects of housing condition,
we conducted 2 (housing condition) by 3 (days) ANOVAs with repeated measures on the second
factor. To assess the effects of level of stereotypy on cognitive function, we conducted 4
(stereotypy group) by 3 (days) ANOVAs with repeated measures on the second factor. For all
dependent variables assessed, there were no differences in sex or age, although there was a
tendency for females and for younger mice (3 months of age) to perform better than males and
older mice (7 months of age).
Effects of Housing Conditions: Enriched vs. Standard Caging
Significant main effects of housing condition were found on latency to reach the platform
(F(1, 100)=11.3, p=0.001) (Figure 3-3A), distance traveled (F(1, 100)=12.0, p=0.001) (Figure 3-
4A), velocity (F(1, 100)=20.5, p<0.001) (Figure 3-5A), the number of first correct entries (F(1,
100)=5.7, p=0.020) (Figure 3-6A), and the number of correct (F(1, 100)=9.0, p=0.004) (Figure
3-7A) and error responses (F(1, 100)=4.3, p=0.044) (Figure 3-8A). With respect to all of these
variables, EE mice performed better than SC mice.
There were also significant main effects of time for all the variables measured: latency
(F(2, 100)= 35.6,p<0.001), distance traveled (F(2, 100)=45.6,p<0.001), velocity (F(2,
100)=35.0, p<0.001), the number of first correct entries (F(2, 100)=22.2 p<0.001), and the
number of correct (F(2, 100)=42.2, p<0.001) and error responses (F(2, 100)=32.1, p<0.001).
No statistically significant interaction was found for latency (F(2, 100)=2.8, p=0.065),
distance traveled (F(2, 100)=1.9, p=0.155), velocity (F(2, 100)=0.3,p=0.739), the number of
first correct entries (F(2, 100)=1.3, p=0.272), and the number of correct responses (F(2,
100)=2.2, p=0.114). A statistically significant interaction was found, however, for error
responses (F(2, 100)=3.6, p=0.031). Specifically, EE and SC mice made a similar number of
error responses in P1, but significant differences between these groups were observed in P2
(p=0.008) and P3 (p=0.043).
Analysis of the first three days of procedural learning does not make use of all the data.
Thus, the number of error responses across all sessions was calculated. A significant difference
in housing condition was found for the number of error responses where SC mice made
significantly more error responses than EE mice (t(50)=-2.3, p=0.025) (Figure 3-9A). However,
the proportion of error responses (the total number of error responses divided by the total number
of responses in the procedural learning experiment) didn't differ between housing conditions
(t(50)=l. 1,p=0.263) (Figure 3-10A).
Finally a main effect of housing condition was found for days required to reach the
criterion, which ranged from 3 to 11 days (t(50)=2.6, p=0.012) (Figure 3-14A). In this, as in all
other measures, mice housed in an enriched environment performed better than mice housed in
standard cages in this procedural task.
In addition, the proportion of animals meeting criterion across totals was calculated by
survival analysis using the Cox proportional hazard model. There was a significant difference
(p=0.024), such that a greater proportion of EE mice met criterion in fewer trials than did SC
mice (Figure 3-15A).
A main effect of housing condition on latency to reach the platform was also observed in
the reversal phase (F(1, 100)=4.2, p=0.046) (Figure 3-3A). As seen in the procedural learning
phase, significant differences between EE and SC mice were also found for the other dependent
measures examined: distance traveled (F(1, 100)=5.8, p=0.020) (Figure 3-4A), velocity (F(1,
100)=6.9, p=0.012) (Figure 3-5A), the number of first correct arm entries (F(1, 100)=8.0,
p=0.007) (Figure 3-6A), and the number of correct (F(1, 100)=9.5, p=0.003) (Figure 3-7A) and
error responses (F(1, 100)=13.8, p<0.001) (Figure 3-8A).
A main effect of time was found on all measures employed: latency (F(2, 100)=42.3,
p<0.001), distance traveled (F(2, 100)=75.2, p<0.001), velocity (F(2, 100)=4.9,p=0.010), the
number of first correct arm entries (F(2, 100)=48.9, p<0.001), and the number of correct
(F(2)=53.8,p<0.001) and error responses(F(2, 100)=87.0,p<0.001). Specifically, EE mice swam
significantly faster on all R1-3 days (p=0.013, p=0.024, andp=0.027 respectively), and made
more correct and fewer error responses in R1 (p=0.013, p=0.010 respectively) and R2 (p<0.001,
p<0.001 respectively) than SC mice. There were no statistically significant interactions for any
of these measures.
In addition, EE mice made significantly fewer error responses compared to SC mice across
all sessions in the reversal phase (t(50)=-3.4, p=0.001) (Figure 3-9A). Similarly, SC mice
exhibited a significantly greater proportion of error responses compared to EE mice (t(50)=3.6,
p<0.001) (Figure 3-10A).
Figure 3-11A shows the proportion of correct responses in the first 24 trials of the reversal
phase. In the first trial of the reversal phase (rl), almost all the mice failed to make a correct
response. Yet, as the trials progressed, EE mice quickly learned the new S-R contingency. By the
end of the first session (r8), the proportion of correct response in SC mice was below chance
level (approximately 25%), whereas the proportion of correct responses for EE mice was
approximately 60%. Similarly, the proportion of error responses during reversal learning was
higher for SC mice compared to EE mice in rl-24 (Figure 3-12A). Finally, there was a main
effect of housing on days to reach criterion (t(50)=2.2, p=0.033) (Figure 3-14A), with mice
housed in the EE condition performing better than mice housed in the SC condition in the
In addition, the proportion of animals meeting criterion across totals was calculated for
survival analysis by the Cox proportional hazard model. There was a significant difference
(p=0.021), such that a greater proportion of EE mice met criterion in fewer trials than did SC
mice (Figure 3-15B).
Effects of Stereotypy Levels
A main effect of stereotypy level was found for latency (F(3, 96)=3.0, p=0.041) (Figure 3-
3B), distance traveled (F(3, 96)=6.9, p<0.001) (Figure 3-4B), and velocity (F(3, 96)=3.3,
p=0.029) (Figure 3-5B). Specifically mice in the backward somersaulting group spent a
significantly longer duration of time in the maze than the low stereotypy group (p=0.029). The
differences in latency between these groups were significant for the first (P1) (p=0.037) and
second (P2) (p=0.003) days. By day three (P3) all stereotypy groups took roughly equal amounts
of time for trial completion. Similarly, mice in the backward somersaulting group traveled the
longest distance to reach the platform compared to any other groups (L, M, and H) (p<0.001,
p=0.003, p=0.002 respectively) (Figure 3-4B). No significant differences among the high,
medium, and low jumpers were noted.
Post hoc analyses for the dependent measure of velocity showed a significant difference
between mice in the backward somersaulting and in the low stereotypy groups (p=0.025) and in
P2 (p=0.043) and P3 (p=0.016). When the velocity of each mouse was compared with their
individual stereotypy frequency score, there was a tendency for mice with high frequency of
stereotypy to swim slower (r=-0.256, p=0.070). This was largely attributed to the swim speed
among mice exhibiting vertical jumping (L, M, and H) (r=-0.292, p=0.057).
A main effect of time was found for all measures: latency (F(2, 96)=38.1, p<0.001),
distance traveled (F(2, 96)=52.1, p<0.001), velocity (F(2, 96)=32.3, p<0.001), the number of
first correct arm entries (F(2, 96)=20.0, p<0.001), the number of correct (F(2, 96)=40.0,
p<0.001) and error responses (F(2, 96)=0.9, p 0.452).
The only measure for which a significant group by time interaction was found was distance
traveled (F(6, 96)=2.8, p=0.015). Mice in the low stereotypy group increased the velocity as the
trials progressed, whereas mice in the backward somersaulting group stayed at relatively slow
speed (Figure 3-5B).
No group differences were found on the number of first correct arm entries (F(3, 96)=1.6,
p=0.205) (Figure 3-6B) and the number of correct (F(3, 96)=2.5,p=0.067) (Figure 3-7B) and
error responses (F(3, 96)=0.9, p=0.452) (Figure 3-8B). In addition, no significant difference was
found in the total number of error responses (F(3)=1.6, p=0.192) (Figure 3-9B) as well as a
proportion of error responses across all sessions in the procedural phase (F(3)=0.3, p=0.861)
Next, each stereotypy score was regressed by the total number of correct or error responses
made within P1-3. There were no relationship between rates of stereotypy and correct (r=-0.094,
p=0.509) and error responses (r=0.045,p=0.750). Moreover, there wasn't any relationship
between stereotypy scores and the total number of correct (r=0.050, p=0.724) and error
responses (r=0.062, p=0.662) made in the procedural phase.
Finally, one-way ANOVA for stereotypy groups showed that significant differences
existed in days to reach the criterion (F(3)=3.7, p=0.018). Post-hoc analyses revealed a
significant difference between mice in the backward somersaulting group and in the low
stereotypy group (p=0.027) (Figure 3-14B).
During reversal training, no significant differences among groups were found for latency
(F(3, 96)=1.2,p=0.335) (Figure 3-3B) or swim speed (F(3, 96)=1.3, p=0.298) (Figure 3-5B).
Conversely, main effects of stereotypy level were found for the variables distance traveled (F(3,
96)=3.1, p=0.036) (Figure 3-4B), the number of first correct arm entries (F(3, 96)=8.8, p<0.001)
(Figure 3-6B), and the number of correct (F(3, 96)=8.9, p<0.001) (Figure 3-7B) and error
responses (F(3, 96)=5.3, p=0.003) (Figure 3-8B).
Specifically, mice in the backward somersaulting group traveled longer distances
(p=0.023), made fewer successful first correct arm entries (p<0.001), and made fewer correct
(p<0.001) and more error responses (p=0.002) than mice in the low stereotypy group. In
addition, low stereotypy mice made significantly more first correct entry and correct responses,
than mice in the medium stereotypy group (p=0.001, p=0.001 respectively) and mice in the high
stereotypy group made more first correct entry and correct responses than mice in the backward
somersaulting group (p=0.042, p=0.047 respectively).
A main effect of time was found for all measures: latency (F(2, 96)=42.5, p<0.001),
distance traveled (F(2, 96)=76.8, p<0.001), velocity (F(2, 96)=5.0, p=0.008), the number of first
correct arm entries (F(2, 96)=49.7, p<0.001), and the number of correct (F(2, 96)=58.5, p<0.001)
and error responses (F(2, 96)=86.9, p<0.001).
A group by time interaction was found for distance moved (F(6, 96)=2.7, p=0.018) (Figure
3-4B), first correct arm entries (F(6, 96)=4.3, p<0.001), and the number of correct (F(6, 96)=6.3,
p<0.001) (Figure 3-7B) and error responses (F(6, 96)=3.9, p=0.002) (Figure 3-8B). This effect
seems to be due to the unexpected performance by mice in the high stereotypy group.
In addition, the number of error responses made in R1-3 was positively correlated with the
frequency of stereotypy (r=0.306, p=0.003) (Figure 3-13). This difference was mainly due to
mice showing vertical jumping (r=0.317, p=0.039). It is worth noting that number of error
responses in the P1-3 and R1-3 was positively correlated in mice exhibiting vertical jumping (L,
M, and H groups) (r 0.310, p=0.043), suggesting that mice exhibiting higher rates of stereotypy
appear to perseverate more and mice with procedural learning deficits exhibit reversal deficits.
However, when the stereotypy score was regressed against the total number of error responses
made by each mouse, no relationship between stereotypy score and error responses was found
In addition, a significant difference was found in the total number of error responses across
sessions in the reversal phase (F(3)=8.1, p<0.001), where mice in the backward somersaulting
group made significantly more error responses than any other groups (L, M, and H) (p<0.001,
p=0.012, p=0.002 respectively) (Figure 3-9B). There was also a significant difference in a
proportion of error responses (F(3)=3.9, p=0.014). Mice in the backward somersaulting group
exhibited a significantly greater proportion of error responses than mice in the low stereotypy
group (p=0.024) (Figure 3-10B).
Figure 3-11B shows the proportion of mice making a correct response in the first 24 trials
of the reversal phase. In the first trial of the reversal phase (rl), almost all of the mice failed to
make a correct response. Approximately 65% of mice in the low stereotypy group made a correct
response in r8 and almost all found the platform successfully by the middle of the second
reversal session, 10% of mice in the backward somersaulting group made a correct response in r8
and the probability stayed below chance level through r24. Similar reversal trends were seen for
an error response in rl-24 (Figure 3-12B).
Finally, significant differences were found in days required to reach a reversal criterion
among different levels of stereotypy (F(3)=8.9, p<0.001) (Figure 3-14B). Mice in the backward
somersaulting group required significantly more days to complete the task than mice in the low
(p<0.001) and high (p=0.003) stereotypy groups. In addition, mice in the middle stereotypy
group required more days than mice in the low (p=0.005) and high (p=0.016) stereotypy groups.
There was no correlation between days required to meet criterion for procedural learning
and days required to meet criterion for reversal learning (r=0.23, p=0.103). However, when the
two topographies of stereotypy were analyzed separately, the number of days to reach both
criteria was not correlated in jumpers (r=-0.025, p=0.874), but were strongly correlated in
backflippers (r=0.765, p=0.016). Therefore these results indicate that for mice exhibiting
repetitive backward somersaulting deficits in procedural learning were associated with cognitive
Figure 3-1. Effects of environmental enrichment on stereotypy (vertical jumping and backward
somersaulting): EE substantially attenuated the development and expression of
stereotypy (p<0.001). Values expressed are group means S.E.M.
H M L B
Figure 3-2. Average stereotypy scores in four stereotypy groups: Mice were categorized into H
(n=15), M (n=14), L (n=14), or B (n=9) groups depending on their topography and
frequency of stereotypy. Values expressed are group means S.E.M.
P1 P2 P3 R1 R2 R3
P1 P2 P3
R1 R2 R3
R1 R2 R3
Figure 3-3. Latency to reach the platform. A) Effects of housing conditions: EE mice reached the
platform significantly faster than SC mice in the first three days of both the
procedural (p=0.001) and reversal (p=0.046) phases. B) Effects of stereotypy levels:
B mice took significantly longer to reach the platform than L mice in the first three
days of the procedural phase (p=0.029). There was no difference between stereotypy
groups in the reversal phase (p=0.335). Values expressed are group means + S.E.M of
eight daily trials.
- --- L
P1 P2 P3 R1 R2 R3
1200- ----"----- B
P1 P2 P3 R1 R2 R3
Figure 3-4. Distance traveled. A) Effects of housing conditions: EE mice swam significantly
shorter distances than SC mice in the first three days of both the procedural (p=0.001)
and reversal (p=0.020) phases. B) Effects of stereotypy levels: B mice traveled
significantly longer distance than any other groups in the first three days of the
procedural phase (p<0.001). B mice traveled significantly longer distance than L mice
in the reversal phase (p=0.023). Values expressed are group means + S.E.M of eight
S40 -- EE
30- --- i --- i --- i --- i ---- ---- -- -- -- --B
P1 P2 P3 R1 R2 R3
P1 P2 P3 R1 R2 R3
Figure 3-5. Velocity. A) Effects of housing conditions: EE mice swam significantly faster than
SC mice in the first three days of the procedural (p<0.001) and reversal (p=0.012)
phases. B) Effects of stereotypy levels: B mice swam significantly slower than L mice
in the first three days of the procedural phase (p=0.029). No group difference was
found in the reversal phase (p=0.298). Values expressed are group means + S.E.M of
eight daily trials.
1- 8 ----i--- L
S a-e /
1- 82- ->- --
u- 4 /
P1 P2 P3 R1 R2 R3
Figure 3-6. The number of first correct arm entries. A) Effects of housing conditions: EE mice
made significantly more correct entries than SC mice in the first three days of both
the procedural (p=0.020) and reversal (p=0.007) phases. B) Effects of stereotypy
levels: Although no group difference was found in the procedural phase (p=0.205), L
mice made significantly more correct entries than B (p<0.001) and M mice (p=0.001),
and H mice made more correct entries than B mice (p=0.042) in the first three days of
the reversal phase. Values expressed are group means + S.E.M of eight daily trials.
P1 P2 P3 R1 R2 R3
P1 P2 P3 R1 R2 R3
W a --y~- M
P1 P2 P3 R1 R2 R3
Figure 3-7. The number of correct responses. A) Effects of housing conditions: EE mice made
significantly more correct responses than SC mice in the first three days of both the
procedural (p=0.004) and reversal (p=0.003) phases. B) Effects of stereotypy levels:
Although no group difference was found in the procedural phase (p=0.067), L mice
made significantly more correct responses than B (p<0.001) and M (p=0.001) mice,
and H mice made more correct responses than B mice (p=0.047) in the first three days
of the reversal phase. Values expressed are group means S.E.M of eight daily trials.
P1 P2 P3 R1 R2 R3
7- I H
W 6 ------- B
P1 P2 P3 R1 R2 R3
Figure 3-8. The number of error responses. A) Effects of housing conditions: SC mice made
significantly more error responses than EE mice in the first three days of both the
procedural (p=0.044) and reversal (p<0.001) phases. B) Effects of stereotypy levels:
There was no group difference in the procedural phase (p=0.452), whereas B mice
made significantly more error responses than L mice in the first three days of the
reversal phase (p=0.002). Values expressed are group means S.E.M of eight daily
-0--- -- H \
C) --U-- L
LU 6 ---4--- B
P1 P2 P3 R1 R2 R3
Figure 3-8. The number of error responses. A) Effects of housing conditions: SC mice made
significantly more error responses than EE mice in the first three days of both the
procedural (p=0.044) and reversal (p<0.001) phases. B) Effects of stereotypy levels:
There was no group difference in the procedural phase (p=0.452), whereas B mice
made significantly more error responses than L mice in the first three days of the
reversal phase (p=0.002). Values expressed are group means + S.E.M of eight daily
H M L B
Figure 3-9. The total number of error responses made in the procedural and reversal phases. A)
Effect of housing conditions: SC mice made significantly more error responses than
EE mice in both the procedural (p=0.025) and reversal phases (p=0.001). B) Effect of
stereotypy levels: There was no significant difference among groups in the procedural
phase (p=0.192), whereas B mice made significantly more error responses than L
(p<0.001), M (p=0.012), and H (p=0.002) mice in the reversal learning. Values
expressed are group means + S.E.M.
0.25 E % R ERRORS
A HOUSING GROUPS
S% P ERROR
0.30 % R ERROR
H M L B
B STEREOTYPY GROUPS
Figure 3-10. The proportion of error responses in the procedural and reversal phase. A) Effects
of housing conditions: There was no difference between groups in the procedural
phase (p=0.263), whereas SC mice exhibited a significantly greater proportion of
error responses than EE mice in the reversal phase (p<0.001). B) Effects of stereotypy
levels: There was no significant difference among groups in the procedural phase
(p=0.861), B mice exhibited a significantly greater proportion of error responses than
L mice in the reversal phase (p=0.024). Values expressed are group means + S.E.M.
rl r2 r3 r4 r5 r6 r7 r8 r9 r10rl1r12r13r14r15r16r17r18r19r20r21r22r23r24
Figure 3-11. Probability of making a correct response in the first 24 trials of the reversal phase.
w. o s l L
behavior, B mice show a pattern ofperseveration.
o o. .
rl r2 r3 r4 r5 r6 r7 r8 r9rlr11r12r13r14r15r16r17r18r19r20r21r22r23r24
Figure 3-11. Probability of making a correct response in the first 24 trials of the reversal phase.
A) Effects of housing conditions: EE mice compared to SC mice quickly learned the
new behavior. B). Effects of stereotypy levels: Although L mice learned the new
behavior, B mice show a pattern of perseveration.
r1 r2 r3 r4 r5 r6 r7 r8 r9 r10r11r12r13r14r15r16r17r18r19r20r21r22r23r24
of *t--- M
U 0.8-- L
z 1 ---- --- B
LU 0.6 0.
(D 0.2 \
rl r2 r3 r4 r5 r6 r7 r8 r9 r10r11r12r13r14r15r16r17r18r19r20r21r22r23r24
Figure 3-12. Probability of making an error response in the first 24 trials of the reversal phase.
A) Effects of housing conditions: EE mice compared to SC mice quickly learned to
the previously relevant response. B) Effects of stereotypy levels: Although L mice
learned to inhibit the previously relevant response, B mice show a pattern of
U) 20 -
0 10 -
U) 20 -
0 200 400 600 800
STEREOTYPY SCORE (JUMPERS)
Figure 3-13. Regression of the total number of error responses in the reversal phase by individual
stereotypy score. A) Stereotypy score was positively correlated with the number of
error responses (p=0.003). B) Stereotypy score was positively correlated with the
number of error responses when six outliers were excluded (p=0.025).
D 500 1000 1500 2000
STEREOTYPY SCORE (JUMPER)
A HOUSING GROUPS
H M L B
B STEREOTYPY GROUPS
Figure 3-14. Days required to reach the criterion. A) Effects of housing conditions: SC mice
required significantly more days to reach the criterion in the procedural (p=0.012) and
reversal (p=0.033) phases. B) Effects of stereotypy levels: B mice spent significantly
more days than L mice to reach the procedural criterion (p=0.027). B mice spent
significantly more days than L (p<0.001) and H (p=0.003) mice, and M mice spent
more days than L (p=0.005) and H (p=0.016) to reach the reversal criterion. Values
expressed are group means + S.E.M.
0 20 60 80 1U
S- landard tt14
0ci 40 60 50 1 1
Figure 3-15. Effects of housing conditions on trials to the criterion. A) Trials to the procedural
criterion: SC mice required significantly more trials to reach the procedural criterion
I I I I I
criterion: SC mice required significantly more trials to reach the procedural criterion
(p=0.021). B) Trials to the reversal criterion: SC mice required significantly more
trials to reach the reversal criterion (p=0.024).
Restricted, repetitive behaviors are commonly displayed in many neurodevelopmental
disorders. Despite their prevalence in clinical populations, relatively little is known about the
neurobiological mechanisms responsible for the development and expression of these behaviors.
A better understanding of the underlying alterations will aid in identifying etiology as well as
developing a better treatment plan for individuals with repetitive behavior disorders. Valid
animal models provide an important strategy in achieving these goals and are necessary for
pursuing the neural mechanisms of this abnormal behavior.
This study employed deer mice (Peromyscus maniculatus) as a model of repetitive motor
behavior associated with neurodevelopmental disorders. These mice exhibit high rates of
repetitive jumping or backward somersaulting when housed in standard rodent cages, and such
behaviors can be attenuated or prevented by housing them in environmentally complex settings
(Powell et al., 2000; Powell et al., 1999). In addition, our work suggests that deer mice exhibiting
high rates of stereotypy have altered cortico-basal ganglia circuitry, specifically relatively
decreased tone of the indirect pathway (Presti & Lewis, 2005).
In this study, we attempted to examine hypothesized impairments in stereotypic deer mice
in cognitive processes that are mediated in part by cortico-basal ganglia circuitry. First, we tested
striatally mediated procedural learning in mice displaying various rates of stereotypy, which
were reared in either a standard rodent cage or an environmentally enriched condition. Since
cortico-striatal circuitry involving the frontal cortex seems to play an important role in executive
function (Dallery et al., 2004; Dias et al., 1996; Uylings et al., 2003; van der Meulen et al.,
2006), we further assessed one aspect of such higher-order function, cognitive flexibility, by
switching of the stimulus-response (S-R) contingency (reversal learning) following acquisition of
the procedural task.
Effects of Housing Conditions on Stereotypy
In agreement with our previous findings (Powell et al., 2000; Powell et al., 1999), deer
mice reared in an environmentally enriched (EE) condition developed significantly lower rates of
stereotypy compared to mice reared in standard cages (SC). One novel feature of this study is
that we categorized mice displaying backward somersaulting as a separate group for statistical
analysis. In past experiments, we have not systematically differentiated these two topographies
(vertical jumps and backward somersaults), because a majority of deer mice exhibited high rates
of repetitive vertical jumps and only a minority engaged in more complex backward somersaults
(Powell et al., 1999).
As expected, most EE mice exhibited low levels of jumping and most SC mice exhibited
high rates of jumping or backward somersaulting. Although we wished to examine the
interaction between housing conditions and levels of stereotypy on cognitive performance, we
were not able to evaluate such effects due to the small number of mice in the EE-high stereotypy
and SC-low stereotypy groups.
Effects of Housing Conditions on Procedural Learning
Studies have repeatedly demonstrated that memory dependent on the hippocampal
formation improves following exposure to EE in animals (Duffy et al., 2001; Lambert et al.,
2005; Pham et al., 1999; Rampon et al., 2000; Winocur & Greenwood, 1999; Woodcock &
Richardson, 2000). Since EE benefits a variety of other behaviors and relevant neurobiology, it is
reasonable to hypothesize that the memory systems mediated by non-hippocampal regions such
as the striatum (procedural learning) also improve following EE. Although there have been
several attempts to examine effects of EE on procedural learning (Frick & Fernandez, 2003;
Frick et al., 2003; Schrijver et al., 2004), no significant improvements were noted.
For example, Frick and colleagues (Frick & Fernandez, 2003; Frick et al., 2003) exposed
aged rats (18 and 28 months) to EE and assessed their performance in two versions (spatial and
cued) of Morris water maze tasks. Rats exposed to EE conditions as adults performed
significantly better than SC control rats in the spatial task, whereas EE did not reduce age-
associated cognitive impairments in the cued task.
In contrast, our results showed that mice reared in EE condition performed significantly
better with respect to all behavioral measurements collected during the procedural task (latency,
distance traveled, velocity, the number of first correct arm entries, and the number of correct and
error responses), and took fewer days to criterion compared to SC mice.
This contradictory result from other groups could be explained by the age and species
difference in sensitivity to surrounding environments. Whereas Frick and colleagues showed that
age-related cognitive impairments in rats were found specifically in the hippocampus and EE
rescued associated deficits in rats, relatively younger deer mice were employed in this study. In
addition, neurobiological alterations associated with repetitive behavior in adult deer mice were
primarily found in the motor cortex and dorsolateral striatum (Turner et al., 2003; Turner et al.,
EE-associated improvements in hippocampally dependent memory are often associated
with elevation of neurotrophic factors in the hippocampus (Pham et al., 1999). We previously
found that deer mice, which benefited from EE, had elevated levels of striatal brain derived
neurotrophic factor (BDNF) (Turner & Lewis, 2003). This neurotrophin plays a particularly
important role in neuronal plasticity associated with learning and memory. In contrast, no
increase in BDNF or nerve growth factor (NGF) was noted within the hippocampus in these
The ameliorative effects of EE, therefore, seemed to act preferentially upon the striatum in
deer mice, resulting in improvements in performance in the procedural-learning task. In
summary, our current and previous work supports improvements of striatally mediated memory
following EE in deer mice.
Effects of Housing Conditions on Reversal Learning
In the reversal experiment assessing cognitive flexibility, EE mice performed significantly
better in all measurements during the first few days of the reversal task. Specifically, SC mice
made significantly more perseverative errors before reaching the criterion. Even after many days
of training trials in the procedural phase, they swam significantly slower and longer distances
during reversal learning, with no obvious motor abnormalities.
Moreover, relatively more EE mice reached the criterion early in training according to the
survival analysis. We found such significant differences for both the procedural and reversal
phases, but the magnitude of difference between the two groups was larger in the reversal phase.
Although we hypothesized an effect of EE on executive function, not many studies have tested
this effect (Jones et al., 1991; Schrijver et al., 2004; Schrijver & Wurbel, 2001).
The studies assessing the effect of EE on cognitive flexibility have focused primarily on
the social component of EE. For example, Schrijver and Wurbel (2001) demonstrated that
socially isolated rats had deficits in extradimensional set-shifting from cue- to place-version of
the radial arm maze tasks, and vice versa. Both the social and isolated rats had intact cue and
place memory as well as intradimensional set-shifting within these tasks, however.
In contrast, we exposed mice to an environment consisting of multiple EE factors (novelty,
inanimate objects, social interaction, exercise, increased space, etc.), and found significant
effects of EE on cognitive flexibility. Thus, these results suggest that a combination of multiple
EE components benefits higher-order cognitive functions dependent in part on cortico-basal
ganglia circuitry in deer mice, in addition to memory systems discussed above.
Effects of Stereotypy Levels on Procedural Learning
Among the four groups constituted by stereotypy level or topography (three levels of
vertical jumping and backward somersaulting), impairments in the procedural task were found in
mice exhibiting backward somersaults. These mice traveled longer distance, swam slower, and
required more days to criterion. There was no relationship between rates of stereotypy and
correct- or error-response frequency suggesting that mice of various levels of stereotypy
explored the maze similarly. Thus contrary to our hypothesis, procedural-learning impairments
in high-stereotypy mice were not found.
Evidence for deficits in striatally mediated learning in autistic individuals is almost
completely lacking, despite the significance of these brain regions in the expression of repetitive
behaviors. However, there has been a report of a deficit in the Serial Response Time Trial task
(Mostofsky et al., 2000) in children with autism. Although performance in this task likely
involves both cortico-striatal and cortico-cerebellar pathways, no attempt was made to relate
reaction time to repetitive behaviors.
We know relatively more about deficits in striatally mediated learning and memory among
individuals with Tourette's syndrome and obsessive-compulsive disorder (OCD). Marsh and
colleagues (2004) recently reported an inverse correlation between tic and habit learning in
children and adults with Tourette syndrome, whereas declarative memory was not different from
healthy controls. Patients with OCD performed better at the early course of procedural learning
but were impaired at the later phase, whereas declarative memory was intact (Roth et al., 2004).
Thus, in these populations, restricted, repetitive behavior is associated with striatal dysfunctions,
which, in turn, are associated with disruptions in striatally mediated learning.
Effects of Stereotypy Levels on Reversal Learning
Of most interest in this experiment was the association between rates of stereotypy and
cognitive rigidity. Our hypothesis came from a series of studies done by Mason and colleagues
(Garner & Mason, 2002; Garner et al., 2003a; Garner et al., 2003b; Vickery & Mason, 2005),
who reported in several species of animals that motor stereotypy associated with a restricted
environment was positively correlated with perseverative behavior. The cognitive tasks
employed included extinction, reversal learning, and a variation of the gambling task.
Similarly, correlations between restricted, repetitive behavior and cognitive rigidity were
recently demonstrated in autistic individuals (Lopez et al., 2005). Although it has been widely
known that these individuals have deficits in executive function (Pennington & Ozonoff, 1996),
its association with restricted, repetitive behaviors had not previously been examined.
Consistent with these findings, our results showed that stereotypy score was positively
correlated with the number of error responses made during the beginning of reversal training as
well as before reaching the criterion. Since error responses made especially during the first few
days is indicative of how quickly, thus flexibly, they switch the learning strategy, the results
support our hypothesis that high rates of stereotypy in deer mice is associated with cognitive
rigidity. Perseverative behavior was prominent in mice displaying backward somersaulting,
which more frequently chose the incorrect arm for their first response.
However, mice in the middle-stereotypy group unexpectedly took as many days as mice in
the backward somersaulting group to reach the reversal criterion, whereas mice in the high- and
low-stereotypy group performed equally. There were nine mice in total, which did not reach the
criterion, and four of them were in the middle-stereotypy group (two mice from each housing
condition). Relatively better performance in mice displaying high rates of jumping was contrary
to our hypothesis. Nonetheless, we did find an association between stereotypy and reversal
In this experiment, no interactions between housing conditions and stereotypy levels could
be examined and interpreted. Therefore, main effects of stereotypy levels on cognitive rigidity
were largely skewed by housing conditions, since a large number of EE mice displayed low rates
and most SC mice exhibited either high-stereotypy jumping or backward somersaulting.
However, of interest is that mice exhibiting backward somersaults performed most poorly in both
the procedural and the reversal tasks than mice displaying vertical jumping. Considering that
they all came from SC condition, we can speculate that cortico-basal ganglia circuitry in these
mice was most perturbed.
It is worth noting that we informally observed that some of the backward somersaulters
failed to swim straight but instead took either a clockwise or a counterclockwise circular pattern
during the visible platform Morris water maze task, which was used as a pretest. Thus we
carefully observed their swim performance to exclude those with motor abnormalities. The
remaining mice in this group, which appeared to be unimpaired in their swimming movements,
swam significantly slower than mice in the low-stereotypy group at the beginning of the
procedural training, suggesting the possibility of slight motor abnormalities. This difference in
swim speed, however, disappeared by the beginning of the reversal training. Thus the motor
disadvantage in these mice seems relatively insignificant.
There is accumulating evidence that the frontal cortex subregions play an important role in
cognitive flexibility, and activation of each area depends on the complexity of the task and types
of set-shifting strategies required. Specifically, the dorsolateral prefrontal cortex or medial
prefrontal cortex, in humans and non-human primates or rodents respectively, appear to subserve
higher-order extradimensional attentional changes, whereas the orbitofrontal cortex (OFC) is
likely to mediate simple intradimensional changes (such as reversal learning) (Dias et al., 1996;
Dias et al., 1997; Kim & Ragozzino, 2005; Ragozzino, 2002; Wallis et al., 2001).
A double dissociation study of neuropsychological task performance revealed that
prefrontal dysfunctions of relatively localized areas are associated with some neuropsychiatric
disorders. Schizophrenic patients have deficits in Wisconsin Card Sorting test (WCST), which
indexes dorsolateral prefrontal cortex impairments, whereas OCD patients perform poorly in the
Object Alternation Test and Gambling Task, which require normal OFC functions (Abbruzzese
et al., 1995; Cavallaro et al., 2003). Yet, these disorders may not be exclusively associated with
independent prefrontal dysfunctions, since both patient group performed poorly in Tower of
Hanoi task (Cavallaro et al., 2003). There are also contradictory reports on OCD patients who
performed poorly in WCST (Head et al., 1989) or were as equally impaired as schizophrenic
patients in the Object Alternation Test (Spitznagel & Suhr, 2002).
Neuroimaging studies support altered patterns of brain activation during executive function
tasks in individuals with autism. These include significantly increased activation of brain
regions, which are not usually involved, in Go/No-Go task, spatial STROOP test, and Set-
Shifting task (Schmitz et al., 2006). One speculation of executive dysfunction in autistic patients
is abnormal neural organization and activation of brain regions, which are not normally recruited
for these tasks.
Thus our results suggest that OFC-striatal circuitry is likely impaired in stereotypic deer
mice, since the cognitive task used involved simple reversal learning. Yet it is apparent that the
OFC is not the only prefrontal region commonly perturbed in individuals with
neurodevelopmental disorders associated with repetitive behaviors. For example, in addition to
cognitive inflexibility, Lopez and colleagues (2005) also reported positive correlation of
restricted, repetitive behaviors with deficits in another component of executive function, working
memory, in autistic individuals. Other cognitive tasks requiring different level of processes (e.g.,
extradimensional set-shifting) using varieties of executive function tasks will further elucidate
the specific loci of impairments and its association with repetitive behaviors.
In addition, as an extension of this study, we should be able to double dissociate impaired
striatum-mediated procedural learning and relatively intact hippocampally mediated spatial
learning in deer mice. It is postulated that EE low- and high-stereotypy mice should not differ in
the task testing spatial memory. Conversely, SC low- and high-stereotypy mice should perform
poorly on this task.
Modeling a Wider Range of Restricted, Repetitive Behaviors
Our findings in the reversal-learning task suggest that deer mice can be used as a model of
not just stereotyped motor behavior but also more complex repetitive behavior. Restricted,
repetitive behaviors displayed in autistic individuals have been conceptually divided into two
clusters: simple motor behaviors (e.g., body rocking, hand flipping, and plate spinning) and more
complex higher-order behaviors (e.g., insistence on sameness and circumscribed interests)
(Turner, 1999). Furthermore, two groups recently reported that factor analyses of 12 items in the
section of repetitive behaviors from Autism Diagnostic Interview-Revised yielded two factors:
repetitive sensorimotor actions and resistance to changes, supporting this categorization
empirically (Cuccaro et al., 2003; Szatmari et al., 2005).
Animal models of restricted, repetitive behavior generally focus on motor stereotypy,
which is easier to measure than more complex behaviors. Cognitive rigidity shown in stereotypic
deer mice in this experiment, especially those of backward somersaulting, resemble resistance to
changes in autistic individuals. Although more systematic investigations are necessary, the
results presented here will allow us to extend our animal model to include not only motor but
also cognitive forms of restricted, repetitive behavior. These results will significantly enhance
the applicability of this model to the wide range of restricted, repetitive behavior typical of
autism and other neurodevelopmental disorders.
LIST OF REFERENCES
Abbruzzese, M., Bellodi, L., Ferri, S., & Scarone, S. (1995). Frontal lobe dysfunction in
schizophrenia and obsessive-compulsive disorder: a neuropsychological study. Brain and
Cognition, 27(2), 202-212.
Allain, H., Lieury, A., Thomas, V., Reymann, J. M., Gandon, J. M., & Belliard, S. (1995).
Explicit and procedural memory in Parkinson's disease. Biomedicine and
Pharmacotherapy, 49(4), 179-186.
Bachmann, I., Audige, L., & Stauffacher, M. (2003). Risk factors associated with behavioral
disorders of crib-biting, weaving and box-walking in Swiss horses. Equine Veterinary
Journal, 35(2), 158-163.
Barnes, T. D., Kubota, Y., Hu, D., Jin, D. Z., & Graybiel, A. M. (2005). Activity of striatal
neurons reflects dynamic encoding and recoding of procedural memories. Nature,
Bodfish, J. W., Symons, F. J., Parker, D. E., & Lewis, M. H. (2000). Varieties of repetitive
behavior in autism: comparisons to mental retardation. Journal of Autism and
Developmental Disorders, 30(3), 237-243.
Bruel-Jungerman, E., Laroche, S., & Rampon, C. (2005). New neurons in the dentate gyms are
involved in the expression of enhanced long-term memory following environmental
enrichment. European Journal ofNeuroscience, 21(2), 513-521.
Carney, R. M., Wolpert, C. M., Ravan, S. A., Shahbazian, M., Ashley-Koch, A., Cuccaro, M. L.,
et al. (2003). Identification of MeCP2 mutations in a series of females with autistic
disorder. Pediatric Neurology, 28(3), 205-211.
Cath, D. C., Spinhoven, P., Hoogduin, C. A., Landman, A. D., van Woerkom, T. C., van de
Wetering, B. J., et al. (2001). Repetitive behaviors in Tourette's syndrome and OCD with
and without tics: what are the differences? Psychiatry Research, 101(2), 171-185.
Cauwels, R. G., & Martens, L. C. (2005). Self-mutilation behaviour in Lesch-Nyhan syndrome.
Journal of Oral Pathology and Medicine, 34(9), 573-575.
Cavallaro, R., Cavedini, P., Mistretta, P., Bassi, T., Angelone, S. M., Ubbiali, A., et al. (2003).
Basal-corticofrontal circuits in schizophrenia and obsessive-compulsive disorder: a
controlled, double dissociation study. Biological Psychiatry, 54(4), 437-443.
Colombo, P. J., Brightwell, J. J., & Countryman, R. A. (2003). Cognitive strategy-specific
increases in phosphorylated cAMP response element-binding protein and c-Fos in the
hippocampus and dorsal striatum. Journal ofNeuroscience, 23(8), 3547-3554.
Cuccaro, M. L., Shao, Y., Grubber, J., Slifer, M., Wolpert, C. M., Donnelly, S. L., et al. (2003).
Factor analysis of restricted and repetitive behaviors in autism using the Autism
Diagnostic Interview-R. ChildPsychiatry and Human Development, 34(1), 3-17.
Dahlqvist, P., Ronnback, A., Bergstrom, S. A., Soderstrom, I., & Olsson, T. (2004).
Environmental enrichment reverses learning impairment in the Morris water maze after
focal cerebral ischemia in rats. European Journal ofNeuroscience, 19(8), 2288-2298.
Dalley, J. W., Cardinal, R. N., & Robbins, T. W. (2004). Prefrontal executive and cognitive
functions in rodents: neural and neurochemical substrates. Neuroscience and
Biobehavioral Reviews, 28(7), 771-784.
Dias, R., Robbins, T. W., & Roberts, A. C. (1996). Primate analogue of the Wisconsin Card
Sorting Test: effects of excitotoxic lesions of the prefrontal cortex in the marmoset.
Behavioral Neuroscience, 110(5), 872-886.
Dias, R., Robbins, T. W., & Roberts, A. C. (1997). Dissociable forms of inhibitory control within
prefrontal cortex with an analog of the Wisconsin Card Sort Test: restriction to novel
situations and independence from "on-line" processing. Journal ofNeuroscience, 17(23),
Duffy, S. N., Craddock, K. J., Abel, T., & Nguyen, P. V. (2001). Environmental enrichment
modifies the PKA-dependence of hippocampal LTP and improves hippocampus-
dependent memory. Learning andMemory, 8(1), 26-34.
Ellinwood, E. H., Jr. (1967). Amphetamine psychosis. I. Description of the individuals and
process. Journal of Nervous and Mental Disease, 144(4), 273-283.
Ernst, A. M., & Smelik, P. G. (1966). Site of action of dopamine and apomorphine on
compulsive gnawing behaviour in rats. Experientia, 22(12), 837-838.
Faherty, C. J., Raviie Shepherd, K., Herasimtschuk, A., & Smeyne, R. J. (2005). Environmental
enrichment in adulthood eliminates neuronal death in experimental Parkinsonism.
Molecular Brain Research, 134(1), 170-179.
Fog, R. (1972). On stereotypy and catalepsy: studies on the effect of amphetamines and
neuroleptics in rats. Acta Neurologica Scandinavica Suppl, 50, 3-66.
Folstein, S. E., & Rosen-Sheidley, B. (2001). Genetics of autism: complex aetiology for a
heterogeneous disorder. Nature Reviews Genetics, 2(12), 943-955.
Frick, K. M., & Fernandez, S. M. (2003). Enrichment enhances spatial memory and increases
synaptophysin levels in aged female mice. Neurobiology ofAgiii,,. 24(4), 615-626.
Frick, K. M., Steams, N. A., Pan, J. Y., & Berger-Sweeney, J. (2003). Effects of environmental
enrichment on spatial memory and neurochemistry in middle-aged mice. Learning and
Memory, 10(3), 187-198.
Frith, C. D., & Done, D. J. (1983). Stereotyped responding by schizophrenic patients on a two-
choice guessing task. Psychological Medicine, 13(4), 779-786.
Garner, J. P., & Mason, G. J. (2002). Evidence for a relationship between cage stereotypes and
behavioral disinhibition in laboratory rodents. Behavioural Brain Research, 136(1), 83-
Garner, J. P., Mason, G. J., & Smith, R. (2003a). Stereotypic route-tracing in experimentally
caged songbirds correlates with general behavioral disinhibition. Animal Behaviour, 66,
Garner, J. P., Meehan, C. L., & Mench, J. A. (2003b). Stereotypies in caged parrots,
schizophrenia and autism: evidence for a common mechanism. Behavioural Brain
Research, 145(1-2), 125-134.
Gobbo, O. L., & O'Mara, S. M. (2004). Impact of enriched-environment housing on brain-
derived neurotrophic factor and on cognitive performance after a transient global
ischemia. Behavioural Brain Research, 152(2), 231-241.
Graybiel, A. M., Canales, J. J., & Capper-Loup, C. (2000). Levodopa-induced dyskinesias and
dopamine-dependent stereotypes: a new hypothesis. Trends in Neurosciences, 23(10
Graybiel, A. M., & Rauch, S. L. (2000). Toward a neurobiology of obsessive-compulsive
disorder. Neuron, 28(2), 343-347.
Greer, J. M., & Capecchi, M. R. (2002). Hoxb8 is required for normal grooming behavior in
mice. Neuron, 33(1), 23-34.
Guillou, J. L., Rose, G. M., & Cooper, D. M. (1999). Differential activation of adenylyl cyclases
by spatial and procedural learning. Journal ofNeuroscience, 19(14), 6183-6190.
Hadley, C., Hadley, B., Ephraim, S., Yang, M. C., & M.H., L. (2006). Spontaneous stereotypy
and environmental enrichment in deer mice (Peromyscus maniculatus): Reversibility of
experience. Applied Animal Behaviour Science, 97, 312-322.
Head, D., Bolton, D., & Hymas, N. (1989). Deficit in cognitive shifting ability in patients with
obsessive-compulsive disorder. Biological Psychiatry, 25(7), 929-937.
Hebb, D. 0. (1949). The Organization ofBehavior. New York: John Wiley & Sons.
Herrero, M. T., Barcia, C., & Navarro, J. M. (2002). Functional anatomy of thalamus and basal
ganglia. Child's Nervous System, 18(8), 386-404.
Heyder, K., Suchan, B., & Daum, I. (2004). Cortico-subcortical contributions to executive
control. Acta Psychologica (Amst), 115(2-3), 271-289.
Hollander, E., Anagnostou, E., Chaplin, W., Esposito, K., Haznedar, M. M., Licalzi, E., et al.
(2005). Striatal volume on magnetic resonance imaging and repetitive behaviors in
autism. Biological Psychiatry, 58(3), 226-232.
Iwamoto, E. T., & Way, E. L. (1977). Circling behavior and stereotypy induced by intranigral
opiate microinj sections. Journal ofPharmacology and Experimental Therapeutics, 203(2),
Jankowsky, J. L., Melnikova, T., Fadale, D. J., Xu, G. M., Slunt, H. H., Gonzales, V., et al.
(2005). Environmental enrichment mitigates cognitive deficits in a mouse model of
Alzheimer's disease. Journal ofNeuroscience, 25(21), 5217-5224.
Jenkins, J. R. (2001). Feather picking and self-mutilation in psittacine birds. Veterinary Clinics
of North America: Exotic Animal Practice, 4(3), 651-667.
Jog, M. S., Kubota, Y., Connolly, C. I., Hillegaart, V., & Graybiel, A. M. (1999). Building neural
representations of habits. Science, 286(5445), 1745-1749.
Jones, G. H., Marsden, C. A., & Robbins, T. W. (1991). Behavioural rigidity and rule-learning
deficits following isolation-rearing in the rat: neurochemical correlates. Behavioural
Brain Research, 43(1), 35-50.
Keller, F., & Persico, A. M. (2003). The neurobiological context of autism. Molecular
Neurobiology, 28(1), 1-22.
Kesner, R. P., Bolland, B. L., & Dakis, M. (1993). Memory for spatial locations, motor
responses, and objects: triple dissociation among the hippocampus, caudate nucleus, and
extrastriate visual cortex. Experimental Brain Research, 93(3), 462-470.
Kim, J., & Ragozzino, M. E. (2005). The involvement of the orbitofrontal cortex in learning
under changing task contingencies. Neurobiology ofLearning andMemory, 83(2), 125-
Knopman, D., & Nissen, M. J. (1991). Procedural learning is impaired in Huntington's disease:
evidence from the serial reaction time task. Neuropsychologia, 29(3), 245-254.
Kramer, J. C., Fischman, V. S., & Littlefield, D. C. (1967). Amphetamine abuse. Pattern and
effects of high doses taken intravenously. Jama, 201(5), 305-309.
Krebs, H. I., Hogan, N., Hening, W., Adamovich, S. V., & Poizner, H. (2001). Procedural motor
learning in Parkinson's disease. Experimental Brain Research, 141(4), 425-437.
Lambert, T. J., Fernandez, S. M., & Frick, K. M. (2005). Different types of environmental
enrichment have discrepant effects on spatial memory and synaptophysin levels in female
mice. Neurobiology ofLearning and Memory, 83(3), 206-216.
Leggio, M. G., Mandolesi, L., Federico, F., Spirito, F., Ricci, B., Gelfo, F., et al. (2005).
Environmental enrichment promotes improved spatial abilities and enhanced dendritic
growth in the rat. Behavioural Brain Research, 163(1), 78-90.
Lewis, M. H. (2004). Environmental complexity and central nervous system development and
function. Mental Retardation and Developmental Disabilities Research Reviews, 10(2),
Lewis, M. H., & Baumeister, A. H. (1982). Stereotyped mannerisms in mentally retarded
persons: Animal models and theoretical analyses. International Review ofResearch in
Mental Retardation, 11, 123-161.
Lewis, M. H., & Bodfish, J. W. (1998). Repetitive behavior disorders in autism. Mental
Retardation and Developmental Disabilities Research Reviews, 4, 80-89.
Lewis, M. H., Gluck, J. P., Beauchamp, A. J., Keresztury, M. F., & Mailman, R. B. (1990).
Long-term effects of early social isolation in Macaca mulatta: changes in dopamine
receptor function following apomorphine challenge. Brain Research, 513(1), 67-73.
Lewis, M. H., Tanimura, Y., Lee, L. W., & Bodfish, J. W. (2006). Animal models of restricted
repetitive behavior in autism. Behavioural Brain Research, 0(0), 0-0.
Lopez, B. R., Lincoln, A. J., Ozonoff, S., & Lai, Z. (2005). Examining the relationship between
executive functions and restricted, repetitive symptoms of Autistic Disorder. Journal of
Autism and Developmental Disorders, 35(4), 445-460.
Lutz, C., Well, A., & Novak, M. (2003). Stereotypic and self-injurious behavior in rhesus
macaques: a survey and retrospective analysis of environment and early experience.
American Journal ofPrimatology, 60(1), 1-15.
Malone, R. P., Gratz, S. S., Delaney, M. A., & Hyman, S. B. (2005). Advances in drug
treatments for children and adolescents with autism and other pervasive developmental
disorders. CNS Drugs, 19(11), 923-934.
Marsh, R., Alexander, G. M., Packard, M. G., Zhu, H., Wingard, J. C., Quackenbush, G., et al.
(2004). Habit learning in Tourette syndrome: a translational neuroscience approach to a
developmental psychopathology. Archives of General Psychiatry, 61(12), 1259-1268.
Mason, G. J. (1991). Stereotypies: a critical review. AnimalBehaviours, 41, 1015-1037.
Mason, G. J. (1993). Age and context affect the stereotypes of caged mink. Behaviour, 127,
McDonald, R. J., & White, N. M. (1994). Parallel information processing in the water maze:
evidence for independent memory systems involving dorsal striatum and hippocampus.
Behavioral and Neural Biology, 61(3), 260-270.
McGreevy, P. D., French, N. P., & Nicol, C. J. (1995). The prevalence of abnormal behaviours in
dressage, evening and endurance horses in relation to stabling. Veterinary Record,
Meehan, C. L., Garner, J. P., & Mench, J. A. (2004). Environmental enrichment and
development of cage stereotypy in Orange-winged Amazon parrots (Amazona
amazonica). Developmental Psychobiology, 44(4), 209-218.
Meloni, I., Bruttini, M., Longo, I., Mari, F., Rizzolio, F., D'Adamo, P., et al. (2000). A mutation
in the rett syndrome gene, MECP2, causes X-linked mental retardation and progressive
spasticity in males. American Journal ofHuman Genetics, 67(4), 982-985.
Militerni, R., Bravaccio, C., Falco, C., Fico, C., & Palermo, M. T. (2002). Repetitive behaviors
in autistic disorder. European Child and Adolescent Psychiatry, 11(5), 210-218.
Missale, C., Nash, S. R., Robinson, S. W., Jaber, M., & Caron, M. G. (1998). Dopamine
receptors: from structure to function. Physiological Reviews, 78(1), 189-225.
Moceri, V. M., Kukull, W. A., Emanual, I., van Belle, G., Starr, J. R., Schellenberg, G. D., et al.
(2001). Using census data and birth certificates to reconstruct the early-life
socioeconomic environment and the relation to the development of Alzheimer's disease.
Epidemiology, 12(4), 383-389.
Mooney, E. L., Gray, K. M., & Tonge, B. J. (2006). Early features of autism: Repetitive
behaviours in young children. European Child and Adolescent Psychiatry, 15(1), 12-18.
Moretti, P., Bouwknecht, J. A., Teague, R., Paylor, R., & Zoghbi, H. Y. (2005). Abnormalities of
social interactions and home-cage behavior in a mouse model of Rett syndrome. Human
Molecular Genetics, 14(2), 205-220.
Mostofsky, S. H., Goldberg, M. C., Landa, R. J., & Denckla, M. B. (2000). Evidence for a deficit
in procedural learning in children and adolescents with autism: implications for cerebellar
contribution. Journal ofInternational Neuropsychological Society, 6(7), 752-759.
Muller, N., Putz, A., Kathmann, N., Lehle, R., Gunther, W., & Straube, A. (1997).
Characteristics of obsessive-compulsive symptoms in Tourette's syndrome, obsessive-
compulsive disorder, and Parkinson's disease. Psychiatry Research, 70(2), 105-114.
Nordstrom, E. J., & Burton, F. H. (2002). A transgenic model of comorbid Tourette's syndrome
and obsessive-compulsive disorder circuitry. Molecular Psychiatry, 7(6), 617-625, 524.
O'Sullivan, R. L., Rauch, S. L., Breiter, H. C., Grachev, I. D., Baer, L., Kennedy, D. N., et al.
(1997). Reduced basal ganglia volumes in trichotillomania measured via morphometric
magnetic resonance imaging. Biological Psychiatry, 42(1), 39-45.
Paban, V., Jaffard, M., Chambon, C., Malafosse, M., & Alescio-Lautier, B. (2005). Time course
of behavioral changes following basal forebrain cholinergic damage in rats:
Environmental enrichment as a therapeutic intervention. Neuroscience, 132(1), 13-32.
Packard, M. G., & Knowlton, B. J. (2002). Learning and memory functions of the basal ganglia.
Annual Review ofNeuroscience, 25, 563-593.
Packard, M. G., & McGaugh, J. L. (1992). Double dissociation of fornix and caudate nucleus
lesions on acquisition of two water maze tasks: further evidence for multiple memory
systems. Behavioral Neuroscience, 106(3), 439-446.
Packard, M. G., & White, N. M. (1991). Dissociation of hippocampus and caudate nucleus
memory systems by posttraining intracerebral injection of dopamine agonists. Behavioral
Neuroscience, 105(2), 295-306.
Parent, A., & Hazrati, L. N. (1995). Functional anatomy of the basal ganglia. I. The cortico-basal
ganglia-thalamo-cortical loop. Brain Research Reviews, 20(1), 91-127.
Park, G. A., Pappas, B. A., Murtha, S. M., & Ally, A. (1992). Enriched environment primes
forebrain choline acetyltransferase activity to respond to learning experience.
Neuroscience Letters, 143(1-2), 259-262.
Pennington, B. F., & Ozonoff, S. (1996). Executive functions and developmental
psychopathology. Journal of Child Psychology and Psychiatry, 37(1), 51-87.
Peterson, B. S., Skudlarski, P., Anderson, A. W., Zhang, H., Gatenby, J. C., Lacadie, C. M., et al.
(1998). A functional magnetic resonance imaging study of tic suppression in Tourette
syndrome. Archives of General Psychiatry, 55(4), 326-333.
Pham, T. M., Soderstrom, S., Winblad, B., & Mohammed, A. H. (1999). Effects of
environmental enrichment on cognitive function and hippocampal NGF in the non-
handled rats. Behavioural Brain Research, 103(1), 63-70.
Pittenger, C., Fasano, S., Mazzocchi-Jones, D., Dunnett, S. B., Kandel, E. R., & Brambilla, R.
(2006). Impaired bidirectional synaptic plasticity and procedural memory formation in
striatum-specific cAMP response element-binding protein-deficient mice. Journal of
Neuroscience, 26(10), 2808-2813.
Poldrack, R. A., Prabhakaran, V., Seger, C. A., & Gabrieli, J. D. (1999). Striatal activation
during acquisition of a cognitive skill. Neuropsychology, 13(4), 564-574.
Powell, S. B., Newman, H. A., McDonald, T. A., Bugenhagen, P., & Lewis, M. H. (2000).
Development of spontaneous stereotyped behavior in deer mice: effects of early and late
exposure to a more complex environment. Developmental Psychobiology, 37(2), 100-
Powell, S. B., Newman, H. A., Pendergast, J. F., & Lewis, M. H. (1999). A rodent model of
spontaneous stereotypy: initial characterization of developmental, environmental, and
neurobiological factors. Physiology and Behavior, 66(2), 355-363.
Presti, M. F., Gibney, B. C., & Lewis, M. H. (2004). Effects of intrastriatal administration of
selective dopaminergic ligands on spontaneous stereotypy in mice. Physiology and
Behavior, 80(4), 433-439.
Presti, M. F., & Lewis, M. H. (2005). Striatal opioid peptide content in an animal model of
spontaneous stereotypic behavior. Behavioural Brain Research, 157(2), 363-368.
Presti, M. F., Mikes, H. M., & Lewis, M. H. (2003). Selective blockade of spontaneous motor
stereotypy via intrastriatal pharmacological manipulation. Pharmacology Biochemistry
and Behavior, 74(4), 833-839.
Presti, M. F., Powell, S. B., & Lewis, M. H. (2002). Dissociation between spontaneously emitted
and apomorphine-induced stereotypy in Peromyscus maniculatus bairdii. Physiology and
Behavior, 75(3), 347-353.
Ragozzino, M. E. (2002). The effects of dopamine D(1) receptor blockade in the prelimbic-
infralimbic areas on behavioral flexibility. Learning and Memory, 9(1), 18-28.
Rampon, C., Tang, Y. P., Goodhouse, J., Shimizu, E., Kyin, M., & Tsien, J. Z. (2000).
Enrichment induces structural changes and recovery from nonspatial memory deficits in
CA1 NMDAR1-knockout mice. Nature Neuroscience, 3(3), 238-244.
Randrup, A., & Munkvad, I. (1967). Stereotyped activities produced by amphetamine in several
animal species and man. Psychopharmacologia, 11, 300-310.
Restivo, L., Ferrari, F., Passino, E., Sgobio, C., Bock, J., Oostra, B. A., et al. (2005). Enriched
environment promotes behavioral and morphological recovery in a mouse model for the
fragile X syndrome. Proceedings of the National Academy of Sciences of the USA,
Roth, R. M., Baribeau, J., Milovan, D., O'Connor, K., & Todorov, C. (2004). Procedural and
declarative memory in obsessive-compulsive disorder. Journal ofInternational
Neuropsychological Society, 10(5), 647-654.
Rutten, A., van Albada, M., Silveira, D. C., Cha, B. H., Liu, X., Hu, Y. N., et al. (2002). Memory
impairment following status epilepticus in immature rats: time-course and environmental
effects. European Journal ofNeuroscience, 16(3), 501-513.
Schmitz, N., Rubia, K., Daly, E., Smith, A., Williams, S., & Murphy, D. G. (2006). Neural
correlates of executive function in autistic spectrum disorders. Biological Psychiatry,
Schneider, T., & Przewlocki, R. (2005). Behavioral alterations in rats prenatally exposed to
valproic acid: animal model of autism. Neuropsychopharmacology, 30(1), 80-89.
Schneider, T., Turczak, J., & Przewlocki, R. (2006). Environmental enrichment reverses
behavioral alterations in rats prenatally exposed to valproic acid: issues for a therapeutic
approach in autism. Neuropsychopharmacology, 31(1), 36-46.
Schrijver, N. C., Pallier, P. N., Brown, V. J., & Wurbel, H. (2004). Double dissociation of social
and environmental stimulation on spatial learning and reversal learning in rats.
Behavioural Brain Research, 152(2), 307-314.
Schrijver, N. C., & Wurbel, H. (2001). Early social deprivation disrupts attentional, but not
affective, shifts in rats. Behavioral Neuroscience, 115(2), 437-442.
Sears, L. L., Vest, C., Mohamed, S., Bailey, J., Ranson, B. J., & Piven, J. (1999). An MRI study
of the basal ganglia in autism. Progress in Neuropsychopharmacology and Biological
Psychiatry, 23(4), 613-624.
Segal, D. S., Kuczenski, R., & Florin, S. M. (1995). Does dizocilpine (MK-801) selectively
block the enhanced responsiveness to repeated amphetamine administration? Behavioral
Neuroscience, 109(3), 532-546.
Shahbazian, M., Young, J., Yuva-Paylor, L., Spencer, C., Antalffy, B., Noebels, J., et al. (2002).
Mice with truncated MeCP2 recapitulate many Rett syndrome features and display
hyperacetylation of histone H3. Neuron, 35(2), 243-254.
Snowdon, D. A., Kemper, S. J., Mortimer, J. A., Greiner, L. H., Wekstein, D. R., & Markesbery,
W. R. (1996). Linguistic ability in early life and cognitive function and Alzheimer's
disease in late life. Findings from the Nun Study. Jama, 275(7), 528-532.
Spires, T. L., Grote, H. E., Varshney, N. K., Cordery, P. M., van Dellen, A., Blakemore, C., et al.
(2004). Environmental enrichment rescues protein deficits in a mouse model of
Huntington's disease, indicating a possible disease mechanism. Journal ofNeuroscience,
Spitznagel, M. B., & Suhr, J. A. (2002). Executive function deficits associated with symptoms of
schizotypy and obsessive-compulsive disorder. Psychiatry Research, 110(2), 151-163.
Sprengelmeyer, R., Canavan, A. G., Lange, H. W., & Homberg, V. (1995). Associative learning
in degenerative neostriatal disorders: contrasts in explicit and implicit remembering
between Parkinson's and Huntington's diseases. Movement Disorders, 10(1), 51-65.
Steiner, H., & Gerfen, C. R. (1998). Role of dynorphin and enkephalin in the regulation of
striatal output pathways and behavior. Experimental Brain Research, 123(1-2), 60-76.
Stern, Y., Gurland, B., Tatemichi, T. K., Tang, M. X., Wilder, D., & Mayeux, R. (1994).
Influence of education and occupation on the incidence of Alzheimer's disease. Jama,
Swaisgood, R. R., White, A. M., Zhou, X., Zhang, G., & Lindburg, D. G. (2005). How do giant
pandas (Ailuropoda melanoleuca) respond to varying properties of enrichments? A
comparison of behavioral profiles among five enrichment items. Journal of Comparative
Psychology, 119(3), 325-334.
Symons, F. J., Butler, M. G., Sanders, M. D., Feurer, I. D., & Thompson, T. (1999). Self-
injurious behavior and Prader-Willi syndrome: behavioral forms and body locations.
American Journal of Mental Retardation, 104(3), 260-269.
Szatmari, P., Georgiades, S., Bryson, S., Zwaigenbaum, L., Roberts, W., Mahoney, W., et al.
(2005). Investigating the structure of the restricted, repetitive behaviours and interests
domain of autism. Journal of Child Psychology and Psychiatry, 47(6), 582-590.
Tarou, L. R., Bloomsmith, M. A., & Maple, T. L. (2005). Survey of stereotypic behavior in
prosimians. American Journal ofPrimatology, 65(2), 181-196.
Taylor, D. K., Bass, T., Flory, G. S., & Hankenson, F. C. (2005). Use of low-dose
chlorpromazine in conjunction with environmental enrichment to eliminate self-injurious
behavior in a rhesus macaque (Macaca mulatta). Comparative Medicine, 55(3), 282-288.
Turner, C. A., & Lewis, M. H. (2003). Environmental enrichment: effects on stereotyped
behavior and neurotrophin levels. Physiology and Behavior, 80(2-3), 259-266.
Turner, C. A., Lewis, M. H., & King, M. A. (2003). Environmental enrichment: effects on
stereotyped behavior and dendritic morphology. Developmental Psychobiology, 43(1),
Turner, C. A., Yang, M. C., & Lewis, M. H. (2002). Environmental enrichment: effects on
stereotyped behavior and regional neuronal metabolic activity. Brain Research, 938(1-2),
Turner, M. (1999). Repetitive behaviour in autism: a review of psychological research. Journal
of Child Psychology and Psychiatry, 40(6), 839-849.
Uylings, H. B., Groenewegen, H. J., & Kolb, B. (2003). Do rats have a prefrontal cortex?
Behavioural Brain Research, 146(1-2), 3-17.
van der Meulen, J. A., Joosten, R. N., de Bruin, J. P., & Feenstra, M. G. (2006). Dopamine and
Noradrenaline Efflux in the Medial Prefrontal Cortex During Serial Reversals and
Extinction of Instrumental Goal-Directed Behavior. Cerebral Cortex, 0(0), 0-0.
van Praag, H., Kempermann, G., & Gage, F. H. (2000). Neural consequences of environmental
enrichment. Nature Reviews Neuroscience, 1(3), 191-198.
van Rijzingen, I. M., Gispen, W. H., & Spruijt, B. M. (1997). Postoperative environmental
enrichment attenuates fimbria-fomix lesion-induced impairments in Morris maze
performance. Neurobiology ofLearning and Memory, 67(1), 21-28.
Vandebroek, I., Berckmoes, V., & Odberg, F. 0. (1998). Dissociation between MK-801- and
captivity-induced stereotypes in bank voles. Psychopharmacology (Berl), 137(3), 205-
Vandebroek, I., & Odberg, F. 0. (1997). Effect of apomorphine on the conflict-induced jumping
stereotypy in bank voles. Pharmacology Biochemistry and Behavior, 57(4), 863-868.
Vickery, S. S., & Mason, G. J. (2005). Stereotypy and perseverative responding in caged bears:
further data and analyses. AppliedAnimal Behaviour Science, 91, 247-260.
Wagner, A. K., Kline, A. E., Sokoloski, J., Zafonte, R. D., Capulong, E., & Dixon, C. E. (2002).
Intervention with environmental enrichment after experimental brain trauma enhances
cognitive recovery in male but not female rats. Neuroscience Letters, 334(3), 165-168.
Wallis, J. D., Dias, R., Robbins, T. W., & Roberts, A. C. (2001). Dissociable contributions of the
orbitofrontal and lateral prefrontal cortex of the marmoset to performance on a detour
reaching task. European Journal ofNeuroscience, 13(9), 1797-1808.
Werme, M., Messer, C., Olson, L., Gilden, L., Thoren, P., Nestler, E. J., et al. (2002). Delta FosB
regulates wheel running. Journal ofNeuroscience, 22(18), 8133-8138.
White, L., Katzman, R., Losonczy, K., Salive, M., Wallace, R., Berkman, L., et al. (1994).
Association of education with incidence of cognitive impairment in three established
populations for epidemiologic studies of the elderly. Journal of Clinical Epidemiology,
White, N. M., & McDonald, R. J. (2002). Multiple parallel memory systems in the brain of the
rat. Neurobiology ofLearning and Memory, 77(2), 125-184.
Will, B., Deluzarche, F., & Kelche, C. (1983). Does post-operative environment attenuate or
exacerbate symptoms which follow hippocampal lesions in rats? Behavioural Brain
Research, 7(1), 125-132.
Williams, B. M., Luo, Y., Ward, C., Redd, K., Gibson, R., Kuczaj, S. A., et al. (2001).
Environmental enrichment: effects on spatial memory and hippocampal CREB
immunoreactivity. Physiology and Behavior, 73(4), 649-658.
Winocur, G., & Greenwood, C. E. (1999). The effects of high fat diets and environmental
influences on cognitive performance in rats. Behavioural Brain Research, 101(2), 153-
Woodcock, E. A., & Richardson, R. (2000). Effects of environmental enrichment on rate of
contextual processing and discriminative ability in adult rats. Neurobiology ofLearning
and Memory, 73(1), 1-10.
Yin, H. H., & Knowlton, B. J. (2006). The role of the basal ganglia in habit formation. Nature
Reviews Neuroscience, 7(6), 464-476.
Young, D., Lawlor, P. A., Leone, P., Dragunow, M., & During, M. J. (1999). Environmental
enrichment inhibits spontaneous apoptosis, prevents seizures and is neuroprotective.
Nature Medicine, 5(4), 448-453.
The candidate was born in Tokyo, Japan to Nobuo and Reiko Tanimura. She has one older
sister, Chie. She completed high school at Meguro Seibi Gakuen in Tokyo. She moved to
California in 1998 and received her Bachelor of Arts in Psychology from California State
University, Sacramento in May 2002 with honors. After working for a short period of time in
Tokyo, she joined the laboratory of Dr. Mark H. Lewis and began her graduate education in
August 2003. Currently she is pursuing her Ph.D. in the Behavioral Neuroscience program at the
University of Florida.