Chp. 11: Sensorimotor Function

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Chp. 11 Sensorimotor Function Hippocampal
Plasticity

• Ovarian hormones can influence motor activity.
• review main components of the motor system
• consider role of hormones in altering motor
  responses by acting on neurons within the basal
  ganglia and cerebellum
• estrogen plays a major role in facilitating motor
  responses an effect seen when comparing females
  at different stages of their estrus cycle or when
  comparing males and females
• Hormones also can influence sensory perception.
• Consider the role of hormones on the process of
  learning and memory.
• review the role of the hippocampus as an
  important structure involved in learning and
  memory processes
• consider the role of gonadal steroids in altering
  the morphology of neurons within the hippocampus,
  and possible differences that exist between males
  and females in learning and memory we will also
  consider the role of adrenal hormones on the
  process of learning and memory, and the link
  between elevated levels of glucocorticoids,
  hippocampal damage and memory loss

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Motor System

• The motor system can be divided into two groups
  of circuits
• pyramidal system consists of pyramidal neurons
  within the cerebral cortex that project to lower
  motorneurons in the brainstem and spinal cord to
  control voluntary movement
• several cortical areas are involved in the
  initiation of movement
• neuronal activity within supplementary motor area
  and premotor cortex precedes activity within the
  primary motor cortex
• neuronal activity in the primary motor cortex is
  associated with the initiation of movement
• pyramidal neurons within the primary motor cortex
  project to, and activate, lower motorneurons in
  the brainstem and spinal cord
• lower motor neurons innervate skeletal muscle
  controlling contraction of various muscle groups
  and the movement of body parts (e.g., movement of
  arm or chewing)

Supplementary Motor Area
Premotor Cortex
Primary Motor Cortex
initiation of movement
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Motor System

• The motor system can be divided into two groups
  of circuits
• extrapyramidal system composed of all other
  projection pathways that influence motor control
• basal ganglia
• cerebellum
• groups of neurons within the brainstem that send
  projections into the spinal cord
• neurons within the basal ganglia and cerebellum
  are interconnected with the cerebral cortex
  through a series of feedback loops--one way in
  which the basal ganglia and cerebellum can
  influence motor responses
• in addition, components of the basal ganglia have
  been linked to cognitive processes (memory)

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Motor System

• Basal Ganglia
• the basal ganglia include caudate nucleus,
  putamen and globus pallidus
• in humans, the caudate nucleus and putamen are
  typically segregated in lower mammals (like the
  rat), the caudate nucleus and putamen are
  combined into one structure
• striatum is a term used to refer to both the
  caudate nucleus and putamen
• corpus striatum refers to the caudate nucleus,
  putamen and globus pallidus
• two additional brain regions are interconnected
  with the basal ganglia--subthalamic nucleus and
  substantia nigra
• the basal ganglia forms a variety of
  interconnected loops with the subthalamic
  nucleus, substantia nigra, thalamus and cerebral
  cortex
• bottom line basal ganglia (and associated brain
  regions) receives input from sensory and motor
  cortices, it processes and integrates the
  information, and then sends the output to
  supplementary and premotor cortices to control
  motor activity

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L
The brain is organized bilaterally--with
similar brain structures present on right and
left sides.
R
Primary Motor Cortex
Striatum
Substantia nigra provides an important source of
dopamine to the striatum
Substantia nigra
In most instances, motor control is contralateral
such that the right primary motor cortex controls
movements on the left side of the body.
control of movement on the left side of the body
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Motor System

• In humans, two clinical syndromes have provided
  insight into the basic function of the basal
  ganglia Parkinsons disease and Huntingtons
  disease
• Parkinsons disease
• dopamine neurons within the substantia nigra
  degenerate leading to increased inhibition of
  motor activity
• individuals with this disorder show several
  symptoms including
• bradykinesia--a reduction in the speed of
  movements
• difficulty initiating and stopping movements
• development of resting tremor--a regular
  involuntary, oscillatory movement of a body part,
  usually hands and extremities

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Motor System

• In humans, two clinical syndromes have provided
  insight into the basic function of the basal
  ganglia Parkinsons disease and Huntingtons
  disease
• Huntingtons disease
• degeneration of neurons within the striatum
  including neurons that synthesize the
  neurotransmitters GABA and acetylcholine
• effect of this cell loss is disinhibition of
  motor activity (increased activity)
• individuals with this disorder show several
  symptoms including
• progressive dementia--cognitive deficits
• choreiform movements--rapid, irrregular flow of
  motion associated with fingers, arms and facial
  muscles effects can include piano-playing
  fexion-extension movements of the fingers,
  elevation and depression of the shoulders and
  hips, crossing and uncrossing of the legs, and
  grimacing movements of the face
• Huntingtons disease is a hereditary disease
  onset of symptoms occurs during the third or
  fourth decade of life (30s and 40s)

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Motor System

• In rodents, dopaminergic projections from the
  substantia nigra to the striatum have been
  implicated in motoric function
• locomotion
• stereotyped behavior
• rotational behavior
• postural asymmetries
• These effects of dopamine are associated with
  dopaminergic receptors within the striatum
  several subtypes are present
• subtypes D1 dopamine receptors and D2 dopamine
  receptors
• Estrogen plays an important role in facilitating
  dopamine neurotransmission within the striatum
  which leads to selective increases in motoric
  function
• changes in motoric function in females at
  different stages of the estrus cycle
• sex differences in motor function

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Motor System

• Different types of drugs have been used to study
  the effects of dopamine activity in the striatum
• apomorphine--dopamine agonist that binds to
  dopamine receptors
• amphetamine--drug that stimulates release of
  dopamine from nerve terminals in the striatum
  secondarily, then the released dopamine will bind
  to dopamine receptors
• haloperidol--dopamine receptor antagonist that
  acts by blocking dopamine receptors (blocks the
  ability of dopamine to bind to its receptor)
• The administration of apomorphine or amphetamine
  increases dopamine activity within the brain
  (including the striatum) two main motoric
  effects are produced
• first, there is an increase in locomotion and
  exploratory behavior
• second, there is an increase in the display of
  stereotyped behaviors--repetitive movements of
  head, whiskers and forelimbs these repetitive
  movements can include chewing movements,
  excessive sniffing, up/down movements of the
  head, and so on

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Motor System

• The administration of apomorphine or amphetamine
  can also induce rotational behavior this
  phenomenon is usually studied in animals in which
  the nigrostriatal dopamine system has been
  damaged unilaterally. Depending on the drug
  that is given, animals will turn in a particular
  direction.

Fewer dopamine terminals in the striatum on the
lesioned side less dopamine available for
release.
R
L
Striatum
Selectively destroy dopamine neurons by
administering a neurotoxin to the substantia
nigra on one side (6-hydroxydopamine)
Substantia nigra
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Motor System
Striatum
Effect
animal turns toward the lesion (away from
striatum that has the greatest activity)
increase in dopamine activity on intact
side (reflects release)
if you administer amphetamine
animal turns away from the lesion (away from
striatum that has the greatest activity)
increase in dopamine activity on both
sides (dopamine receptor activation)
if you administer apomorphine
receptor supersensitivity
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Motor System

• Amphetamine stimulates dopamine release more
  dopamine will be released on the intact side
  (greater activity) animal will turn toward
  lesion.
• Apomorphine stimulates dopamine receptors
  reduced levels of dopamine on the lesioned side
  leads to an increase in dopamine receptors more
  dopamine receptors will be activated on lesioned
  side (greater activity) animal will turn away
  from lesion.

amphetamine
Decreased levels of dopamine produce
a compensatory increase in dopamine receptors in
the striatum on the lesioned side.
Turning
apomorphine
R
L
Striatum
Dopamine receptor
Substantia nigra
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Motor System

• Bottom line changes in gonadal steroids that
  occur during the estrus cycle (primarily the rise
  in estrogen) stimulates release of dopamine
  within the striatum that leads to alterations in
  the behavior of the female rat.
• estrogen levels are elevated during late
  proestrus-early estrus (prior to, and during the
  start of behavioral estrus and ovulation)
  estrogen levels are lower at other times (e.g.,
  diestrus)
• dopamine synthesis and release within the
  striatum is greatest during estrus
• administration of amphetamine can stimulate
  greater release of dopamine in the striatum of
  female rats in estrus in comparison to females in
  diestrus this can be seen in tissue slices of
  striatum that are placed into a tissue chamber
  and perfused with amphetamine this can also be
  seen in freely moving rats using microdialysis to
  sample dopamine release within the striatum after
  administration of amphetamine
• administration of amphetamine produced greater
  levels of stereotyped behavior (such as sniffing
  and head and forelimb movements) in female rats
  in estrus in comparison to those in diestrus

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Motor System

• administration of amphetamine also produced
  greater amounts of rotational behavior in females
  during estrus in comparison to females in
  diestrus
• removal of the ovaries (ovariectomy) reduces
  estrogen levels in female rats and will decrease
  stereotypy and rotational behavior induced by
  drugs
• associated with this decline in behavior is a
  decrease in the release of dopamine by
  amphetamine in ovariectomized females
• administration of estrogen to ovariectomized
  females will enhance dopamine-related behaviors
  and increase dopamine release within the striatum
  in response to amphetamine

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Motor System

• The effects of estrogen on striatal activity can
  also be seen in spontaneous behaviors
• you can train female rats to walk across a narrow
  beam suspended about 3 feet above the floor task
  that reflects sensorimotor coordination
• you can analyze how well the female does on this
  task by examining the accuracy of foot placement
  on the beam--if the foot was placed on top of the
  narrow beam--correct, if the foot slipped off
  the top or grabbed onto the side--footfault
• Does performance on this task change over the
  estrus cycle?
• YES--the number of footfaults decrease during
  estrus the female rat performs better on task
  when estrogen levels are high
• you can reproduce this effect by administering
  estrogen directly into the striatum

implant cholesterol into striatum (control)
no effect on footfaults
OVX female rats
train females to walk on beam
significant decline in footfaults
implant estrogen into striatum
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Motor System

• How does estrogen induce its effects at the level
  of the striatum?
• its is presently unknown
• there are few neurons in the striatum that
  accumulate estrogen (few estrogen receptors)
• effects of estrogen may be nontraditional, that
  is, estrogen may act at the membrane of nerve
  terminals to enhance dopamine release versus
  control of gene transcription there is evidence
  for rapid effects of gonadal steroids on
  membranes (but we dont know, in most cases, how
  these rapid effects occur)
• it is possible that estrogen may alter other
  neurocircuits that project to the striatum and
  that regulate dopamine release (e.g., frontal
  cortex)
• it is also possible that estrogen may influence
  the amount of dopamine available for release
  there are dopamine neurons within the substantia
  nigra that possess estrogen receptors
• however, these latter observations do not explain
  how estrogen implants within the striatum can
  alter dopamine release and behavior

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Motor System

• In addition to differences in the behavior of
  female rats during different days of the estrus
  cycle, there are sex differences in the
  activation of motoric responses by drugs
• male rats show lower rates of rotational
  behavior, locomotor activity, and stereotypy in
  response to amphetamine than do female rats in
  estrus
• male rats also show lower level of dopamine
  release in response to amphetamine than do female
  rats in estrus
• castration of male rats has no effect on motoric
  responses nor on striatal dopamine release
• in contrast, ovariectomy in female rats
  significantly decreases amphetamine-induced
  dopamine release in the striatum and
  amphetamine-stimulated motoric behaviors
• important link between estrogen and
  dopamine-responsiveness in females

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Motor System

• There are also differences between males and
  females in a more natural setting--open-field
  activity test.
• In the open-field activity test, a rat is placed
  in a large open testing arena and the amount of
  time spent walking around (ambulation) and
  rearing can be determined
• females ambulate and rear more than males
• ovariectomy decreases these responses, while
  castration has no effect in males
• The relationship between estrogen and increases
  motoric responses in the adult is associated with
  organizational and activation effects
• androgens/estrogens need to be low during
  perinatal development for feminization of this
  behavioral response (organizational effect)
• increases in estrogen that occur in females
  during estrus cycle are needed to produce high
  levels of open-field activity in the adult
• The significance of estrogen-stimulated motoric
  responses may be associated with finding a mate
  and/or motoric responses involved with mating.

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Motor System

• Cerebellum
• the cerebellum receives sensory and motor input,
  processes the information, and then sends its
  output (via Purkinje cells) to deep cerebellar
  nuclei which integrate the input with other motor
  control systems
• bottom line cerebellum is involved primarily in
  controlling the timing and pattern of muscles
  activated during movement, postural support and
  maintenance of muscle tone
• Purkinje cell firing is correlated with movement
  (electrophysiological studies)
• gonadal steroids have been shown to modulate the
  firing of Purkinje cells during movement
• estrogen increases firing rate of Purkinje cells
• progesterone decreases the firing rate of
  Purkinje cells

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Motor System

• Cerebellum
• it has been suggested that the rise in estrogen
  followed by the rise in progesterone may play a
  role in sensorimotor gating in the
  cerebellum--influencing how the cerebellum
  responds to sensorimotor input and its role in
  controlling motor output
• the increases in estrogen and proesterone occur
  during late proestrus to early estrus and are
  associated with changes in proceptive and
  receptive (lordosis) responses it is possible
  that changes occurring in Purkinje cell firing
  rates are associated with proceptive and
  receptive behaviors although, how this occurs is
  not known
• of interest, progesterone can bind to GABA-A
  receptors to potentiate the effects of GABA at
  its receptor
• GABA is an inhibitory neurotransmitter that acts
  to increase chloride (Cl-) conductance into the
  cell, with a net effect of increased inhibition
• the binding of progesterone to the GABA-A
  receptor is thought to mediate the decrease in
  Purkinje cell firing that occurs when
  progesterone levels are high

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Sensory Perception

• In addition to hormonal effects on motor
  responses, hormones can also influence sensory
  perception.
• the vomeronasal organ mediates detection of
  pheromones that stimulate various responses such
  as activation of sex behavior or preferences for
  odors on gonadally-intact conspecifics
• gonadectomy decreases these responses
• administration of testosterone to males, and
  estrogen to females, can restore these responses
• There is also evidence that hormones can
  influence taste and pain sensitivity.
• female rats show a greater preference for sweet
  tastes and salt solutions than males
• stress-induced analgesia (opioid-dependent form)
  is greater in males than in females
• female rats are more responsive to electric
  footshock than males during footshock, females
  respond to lower intensities of shock (lower pain
  thresholds) and react more quickly (shorter
  escape latencies)

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Hippocampus

• Major cellular components
• dentate gyrus (major source of inputs)
• Ammons horn fields CA1, CA2, CA3/CA4
  (integrative role)
• subiculum (major source of efferents)
• Major pathways and connections
• hippocampus receives highly processed sensory
  information about internal and external events
• perforant pathway hippocampus is reciprocally
  connected to the entorhinal cortex entorhinal
  cortex has connections with other corticial
  areas (visual, auditory information)
• fimbria-fornix hippcampus is also reciprocally
  connected to septum, thalamus and hypothalamus
• several pathways that allow for intrahippocampal
  connections
• commissural connections neuronal connections
  made between neurons in two hippocampi
• Schaffer collaterals connections between
  neurons made on one side of hippocampus

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Hippocampus

• Hippocampus plays an important role in two main
  processes
• learning and memory
• especially tasks that involve processes of
  spatial cues
• evidence for sex differences in hippocampal
  structure
• also evidence for sex differences in the
  performance of spatial tasks gonadal steroids
  have been implicated in organizational and
  activational effects on performance
• in the adult, changes in hippocampal structure
  accompany hormone changes during estrus
• brake on HPA axis
• hippocampus possesses mineralocorticoid and
  glucocorticoid receptors
• mineralocorticoid receptors are linked to
  circadian changes in HPA axis
• glucocorticoid receptors are linked to
  terminating a stress response
• chronic exposure to glucocorticoids can damage
  the hippocampus leading to higher levels of
  glucocorticoids, more hippocampal damage, and so
  on damage to the hippocampus has been linked to
  memory deficits

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Hippocampus

• Patient H.M.
• H.M. suffered from intractable epilepsy
  (epileptic seizures)
• an epileptic seizure means that a large
  collection of neurons in the brain discharge in
  abnormal synchrony--seizures can be focal that
  spread throughout cortex or generalized, and may
  involve loss of consciousness as well as
  contraction of groups of skeletal muscle
• intractable means that his epileptic seizures
  were resistant to treatment
• to stop his epileptic seizures, heunderwent
  bilateral hippocampectomy--bilateral removal of
  his hippocampi
• following surgery
• GOOD NEWS his epilepsy stopped
• BAD NEWS while he could remember events early
  in his life, he could not remember events just
  prior to surgery (mild form of retrograde
  amnesia), and he was unable to form new memories
  (anterograde amnesia)

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Hippocampus

• Patient H.M.
• these events in Patient H.M. highlight the
  important role that the hippocampus plays in the
  processes of learning and memory
• mild form of retrograde amnesia and anterograde
  amnesia indicates that the hippocampus plays an
  important role in learning and in the formation
  of short-term memory (working memory)
• however, the ability of H.M. to remember early
  events in his life indicates that the hippocampus
  is not the location where long-term memories are
  stored

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Hippocampus

• What processes have been implicated in learning
  and memory?
• long-term potentiation (LTP)
• an increase in neural activity at particular
  synapses will strengthen those synapses
• this strengthening process involves an in crease
  in synaptic efficacy which simply means that a
  greater synaptic response will be produced in
  response to a given input
• response is believed to last from hours to days
  (short-term responses)

one action potential
little neural activity
little NT released
weak synapse
lots of neural activity
one action potential
strong synapse
lots of NT released
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Hippocampus

• changes in neuronal morphology
• an increase in neural activity will lead to an
  increase in neuronal connections
• this strengthening process involves increasing
  synaptic input and the dendritic complexity of
  neurons 1) more synapses, 2) more dendritic
  spines, 3) increase in length and branching of
  dendrites
• response can last from days to weeks to years
  (short and long-term responses)

little neural activity
lots of neural activity
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Hippocampus

• Learning and Memory
• cellular mechanisms are varied but can involve
• enhanced neurotransmission within
  synapse--increase in synaptic efficacy this is
  thought to reflect an increase in release of
  neurotransmitter
• formation of new connections
• these cellular mechanisms of learning and memory
  have been observed within the hippocampus
• these changes are thought to reflect learning and
  formation of short-term memories especially
  associated with tasks involving spatial cues
• similar plastic events have also been observed
  within other brain areas including the cerebral
  cortex (e.g., visual cortex) and cerebellum

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Hippocampus

• Do gonadal steroids affect neuronal morphology in
  the hippocampus?
• Answer--yes!
• There is evidence that elevations in estrogen and
  progesterone can regulate the number of dendritic
  spines on neurons in the hippocampus in adult
  female rats.
• Study by Gould et al. (1990)
• Question Does estrogen and progesterone
  regulate spine density in neurons within the
  hippocampus?
• spine density number of spines per length of
  dendrite number of synapses on spines

Synapses
dendritic shaft
axosomatic
axoaxonal
axodendritic
dendritic spine
spine
shaft
dendrite
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Hippocampus

• Methods
• adult female rats intact, OVX oil, OVX
  estrogen, OVX estrogen progesterone
• euthanized animals and stained brain tissue with
  Golgi technique--silver stain that fills the
  dendrites, cell bodies and axons of specific
  neurons
• measured the number of spines per length of
  apical or basilar dendrites of neurons in CA1,
  CA3, and dentate gyrus in female rats
• Results
• ovariectomy produced a significant decrease in
  spine density in apical dendrites of neurons
  within CA1 region of hippocampus
• administration of estrogen or estrogen plus
  progesterone produced a significant increase in
  spine density in the apical dendrites of CA1
  region of hippocampus
• the effect was specific to CA1 region of
  hippocampus no change occurred in CA3 region or
  in dentate gyrus
• the effect was rapid occurring after only two
  days of estrogen and 5 hours of progesterone

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Hippocampus

• Conclusion
• the levels of estrogen and progesterone can
  affect the number of spines present within a
  select group of neurons within the hippocampus
  (CA1 region) of adult female rats
• Subsequent studies have shown that such changes
  in spine density also occur with the natural
  fluctuation in hormones that takes place during
  the estrus cycle.
• high estrogen and progesterone levels high
  spine density (late proestrus/early estrus)
• low estrogen and progesterone levels low spine
  density
• these changes are occurring in adult female rats
  every four or five days

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Hippocampus

• Are there sex differences in the structure of the
  hippocampus?
• Answer--yes! There is evidence for a complex
  interaction between early experience (rearing),
  dendritic morphology and sex of individual
  (rats).
• animals raised in an enriched environment possess
  neurons that are more complex than animals raised
  under normal laboratory conditions an enriched
  environment involves the presence of other
  animals and various objects to interact with,
  while normal laboratory conditions are more
  plain and animals may be housed alone or in small
  groups with no objects to play with
• if you compare males and females housed in the
  complex environment to rats housed under normal
  laboratory conditions, you can see several
  differences
• in the apical dendritic tree of CA3 neurons,
  females housed in the enriched environment have
  more dendrites concentrated proximal (close) to
  the cell body, while males in the enriched
  environment had more dendrites concentrated
  distal (far) from cell body
• in the dentate gyrus, females housed in enriched
  environments had granule cells with an increase
  in dendritic length while males in a similar
  environment did not show this change

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Hippocampus

• Are there sex differences in learning and memory?
• Answer--yes!
• There are numerous examples of differences
  between males and females in performance on
  various tests of learning and memory.
• Males are better at passive avoidance learning
  than females (e.g., males learn more quickly to
  not leave a platform because they will get
  shocked).
• Females are better at active avoidance learning
  than males (e.g., females learn to respond more
  quickly to a cue such as a light or tone that
  signals that they should move to another part of
  a chamber to avoid being shocked).
• However, Beatty has argued that such differences
  may simply reflect sex differences in activity.
  That is, females are more active than males and
  as a consequence they may do better on active
  avoidance tasks because of an increased
  likelihood of making the association between
  movement to a given part of a chamber , cue
  presentation and a decrease in shock. Females
  may do more poorly on passive avoidance tasks
  because of they cant sit still.

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Hippocampus

• Are there sex differences in learning and memory?
• It is thought that performance on other more
  complex tasks, such as radial arm maze or the
  Morris water maze, may be less influenced by sex
  differences in activity.
• Maze tasks are considered tests of spatial
  abilities in rodents because animals solve these
  maze tasks by using cues from the surroundings
  outside of the maze.
• The hippocampus (in rats) is thought to be
  essential for solving tasks that require the
  animal to use its spatial abilities.
• There is evidence that males tend to perform
  better on spatial tasks than females.
• This sex difference in seen in some species but
  not all.
• This difference is also somewhat
  limited--greatest sex differences are observed
  during acquisition of the task, and often fewer
  differences are seen once the task has been
  learned.
• It has been suggested that males and females used
  different cues to solve spatial tasks (which may
  underlie differences in acquisition), and there
  is evidence to suggest that exposure to gonadal
  steroids during development and in the adult can
  alter what cues are used to solve a given task.

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Hippocampus

• Study by Williams et al. (1990)
• Question Does exposure to androgens or
  estrogens early in life affect spatial abilities
  in adulthood?
• Methods
• 4 groups male rats castrated on day 1 (MNC),
  sham-operated control males (MC), female rats
  exposed to estrogen from days 1-10 (FNE), and
  sham-operated control females treated with oil
  (FC)
• at 45 days of age, all groups were gonadectomized
  (MNC group was already castrated) this was done
  to control for any activational effects of on
  performance
• at 70 days of age, all rats were placed on a food
  deprivation schedule that kept tham at 85 of
  their free-feeding body weight rats were trained
  to run down arms of the maze for food
• tested the performance of the rats on locating
  food pellets when only some of the arms were
  baited--12-arm maze, 8 arms were baited with food
  and 4 arms were not this relationship remained
  constant throughout the experiment

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Hippocampus

• Study by Williams et al. (1990)
• Methods
• they determined how well animals performed on
  this task by analyzing number of errors made
  until all food pellets were obtained
• 2 types of errors 1) remembering not to go into
  unbaited arms, and 2) remembering what arms were
  visited on a given day (1 test per day for 18
  days)
• Results
• males and masculinized females showed faster
  acquisition of maze task than did females or
  feminized males
• however, after acquisition, no sex differences in
  performance were observed

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Hippocampus

• Study by Williams et al. (1990)
• Question Why are males and females different in
  acquisition of the radial arm maze? Do these
  differences reflect the cues that males and
  females use to solve the task?
• Methods
• similar groups as before 4 groups male rats
  castrated on day 1 (MNC), sham-operated control
  males (MC), female rats exposed to estrogen from
  days 1-10 (FNE), and sham-operated control
  females treated with oil (FC) all groups were
  gonadectomized
• trained the animals on the radial arm maze until
  high performance levels were obtained
• they changed either landmark cues, geometry or
  both and tested the performance of the animals on
  task
• landmark cues cues located within or around a
  maze (table, chair, transport cart) they
  manipulated these cues by rearranging items or
  removing them
• geometric cues shape of room (corners of room)
  manipulated geometry by enclosing the maze within
  a black circular arena

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Hippocampus

• Study by Williams et al. (1990)
• Results
• males and androgenized females used primarily
  geometry to solve the task
• females and feminized males used both geometry
  and landmarks in performing task
• Conclusions
• males use fewer cues (geometry) to solve the
  radial maze than females (geometry and landmark
  cues)
• the need to learn fewer cues may explain why
  males acquire the task more quickly than females
• enhanced spatial ability in males is promoted by
  perinatal exposure to gonadal steroids--1)
  castration of newborn males decreased rate of
  acquisition, and 2) administration of estrogen to
  newborn females within first 10 days of life
  increased rate of acquisition
• after acquisition, no sex differences in
  performance were observed

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Hippocampus

• Sex differences in maze performance have been
  associated with sex differences in brain
  structure--hippocampus.
• Study by Jacobs et al. (1990) compared the size
  of the hippocampus in two species of prarire
  voles that show sex differences in performance on
  spatial tasks.

Spatial Task
Hippocampus
males perform better than females
11 larger in males than in females
meadow vole
no sex difference in performance on task
no sex difference in size of hippocampus
pine vole
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Hippocampus

• Performance on spatial tasks can also be affected
  by hormones in the adult.
• In males
• maximal performance on some spatial tasks are
  seen in males only after puberty (rise in
  testosterone levels)
• increase in spine density in CA1 neurons of male
  mice observed after puberty
• In females
• performance on spatial tasks can be altered
  during estrus cycle

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Hippocampus

• Study by Warren Juraska (1997)
• Question Does performance on spatial tasks by
  females vary with their estrus cycle?
• Methods
• several groups of animals were studied, but they
  focused primarily on females during 2 stages of
  the estrus cycle in 2 forms of the Morris water
  maze
• 2 main groups of females females in late
  proestrus (elevated estrogen levels) versus
  females in late estrus (estrogen levels are low)
• Morris water maze requires that an animal learn
  to find a platform submerged under water (water
  is murky--not a visual task)
• place form of maze--females had to use spatial
  cues surrounding the maze to find platform
  (spatial task)
• cued form of maze--a black ball was suspended
  above the platform, so females had to learn to
  find platform by going toward black ball (cued
  task)

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Cued Task
Spatial Task
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Hippocampus

• Study by Warren Juraska (1997)
• Methods
• animals received pretraining trials on either the
  spatial task or the cued task
• on the day of the experiment, females in late
  proestrus or late estrus received 8 trials, 1
  hour break, followed by 8 additional trials
• how quickly did they find the platform?
• Results
• on spatial task, late estrus females found
  platform more quickly than late proestrus females
• on the cued task, late proestrus females found
  platform more quickly than late estrus
• Conclusions
• the increase in estrogen during late proestrus
  (when there is an increase in dendritic spines)
  is associated with decreased performance on the
  spatial task, but increased performance on the
  cued task

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Hippocampus

• Overall Summary
• sex differences can be seen in tasks involving
  spatial learning and memory
• in males
• increased performance may be associated with the
  use of fewer cues to learn the task (geometry)
• gonadal steroids have an organizing effect on
  spatial ability
• rise in testosterone at puberty may also act to
  enhance spatial abilities (at least on some
  tasks)--activating effect
• in females
• decreased performance may be associated with
  learning more and possibly different cues
  associated with a spatial task
• in adults, increased estrogen (and associated
  changes in spine density in the hippocampus)
  appears to inhibit performance on tasks requiring
  use of spatial cues but may enhance
  responsiveness to other cues

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