Transcript Group 3, Week 10

The Role of the Basal
Ganglia in Habit Formation
By Henry H. Yin & Barbara J. Knowlton
Group 3, Week 10
Alicia Iafonaro
Kimberly Villalva
Tawni Voyles
1. Discuss the relationship of BG and hippocampus to place and
response strategies.
Poldrack and Packard argued that direct or indirect neural connections
between the hippocampus and dorsal striatum could mediate the
competition between them.
Tolman, Packard, and McGaugh- trained rats to retrieve food from one arm
of a cross maze surrounded by various environmental cues.
• After training it is given a probe test- starting arm is placed at the
opposite end of the maze.
• If the rat used the response strategy and turned left, shows that the
learning was inflexible and response-specific. If the rat used the place
strategy and turned right, shows that the animal was able to in corporate
surrounding spatial cues in deciding (choose opposite of what was
learned in training).
1. Discuss the relationship of BG and hippocampus to
place and response strategies.
Results
• Most rats used the place strategy during the probe test, but after extensive
training they switched to a response strategy.
• Rats were more likely to use the place strategy despite extended training
showed inactivity of the dorsal striatum.
• Rats who used the response strategy more frequently, even early in
training showed inactivity of the hippocampus.
Support for Poldrack and Packard idea of the dorsal striatum and the
hippocampus can be viewed as competing learning systems because each
strategy used inactivity in either the dorsal striatum or hippocampus.
1. Discuss the relationship of BG and hippocampus to
place and response strategies.
The authors suggest that the hippocampus does not compete with or
function independently of the dorsal striatum. They can act together with
other regions, such as the medial and ventral striatal regions form a
function circuit.
• DSM contains special selective neurons that fire when animals take a particular
route to reach a goal.
• Contains head- direction neurons with activity aligned with that of the place
fields of hippocampal place cells.
• Information about current position provided by
these cells can be used to signal where to go to
reach a definite goal.
• This information is suggest that is information is
conveyed to the DMS via the cortico-striatal
projection from the hippocampal pyramidal neurons.
2. How does performance learning in different tasks tell us something
about the different functions of the two learning systems? . . .
•There is a dissociation between declarative learning (dependent on the
MTL) and non-declarative (habit) learning (dependent on striatum).
In the Probabilistic Clarification Task:
Patients w/ Parkinson's:
Patients w/ Amnesia:
•These patients had abnormal striatal
functioning due to loss of
dopaminergic input.
•Impaired in the implicit learning of
these associations, although they
achieved normal levels of
performance with further training
•Learned associations normally,
independently of MTL structures that
support declarative memory.
•Assumed to rely on non-declarative
learning.
•MRI: showed activation in the
hippocampus & surrounding MTL
cortical regions.
•Achieved good performance by
relying on declarative memory.
Control Participants:
•Activation in striatal regions during
learning.
•Relied on non-declarative learning
mechanisms.
. . . Are the two systems always operating in a
mutually exclusive way?
•Results suggest that multiple neural systems can support
learning in the probabilistic clarification task.
•Many real world tasks encountered by humans probably
involve BOTH habit and declarative learning.
•The system that contributes most to performance depends on:
•The amount of training
•The ease of memorizing associations between stimuli
•The relative integrity of the basal ganglia and the medial
temporal lobe in the learner.
3. What evidence suggest that the picture of BG function
in learning is more complex than simple habit formation?
How does “habit formation” fail to describe this function?
Despite the evidence for basal ganglia involvement in habit
learning, many findings cannot be explained by the idea that
the dorsal striatum is the substrate of this type of learning.
Studies from caudate cells in monkeys
• the neural activity encoding the preferred direction of saccade
could change according to whether that direction is rewarded,
and this activity is rapidly modified as new contingencies are
encountered
• recording from the prefrontal cortex (PFC) and caudate has
shown that caudate activity rapidly adapts to the contingency
before PFC activity does, and even before significant
improvements in performance occur
3. What evidence suggest that the picture of BG function
in learning is more complex than simple habit formation?
How does “habit formation” fail to describe this function?
Such data suggest that:
• Certain learning mechanisms in the striatum do not
have the characteristics of habit learning
• Anticipation of future rewards has a crucial role in
regulating striatal activity
Changes in neural activity, as a result of learning,
occurred at a rate too rapid to be explained by the
slow and gradual changes posited by traditional S-R/
reinforcement theory. Showing its failure to describe
habit formation.
4. Use some diagrams to make clear the anatomy:
“The caudate in primates
is part of the ‘associative
striatum’, which receives
inputs from association
cortices. It corresponds to
the dorsomedial striatum
(caudate) in rodents,
whereas the putamen is
part of the sensorimotor
striatum, corresponding
to the dorsolateral
striatum (putamen) in
rodents.”
5. Discuss physical and functional differences
between DLS and DMS systems.
• Dorsal Striatum is made up of:
• Caudate (medial) (upper left)
• Putamen (lateral) (right)
• Globus Pallidus (ventral)
(lower left)
• DLS & DMS differ in:
• Connectivity
• Distribution of various
receptors
• Mechanisms of synaptic
plasticity
Dorsolateral Striatum (DLS)
•
•
•
Involved in stimulusresponse learning
Controls movement and is
connected to sensorimotor
functioning (seeing,
hearing, moving, etc.)
For example, when we
move a part of our body in
a new way and it feels
good, for example salsa
dancing, the dorsolateral
striatum is active.
Dorsomedial Striatum (DMS)
• Involved in action-outcome
learning
• Controls flexible behavior and
is connected to areas where
associations are recognized
and formed
• Belongs to the same functional
system as the hippocampus.
• For example, When we feel a
sense of accomplishment for
having tried something new,
the association is recognized
in the dorsomedial striatum.
6. Explain this statement: “It appears that because their habit
system was disrupted by the lesion, the alternative A-O system
assumed control over behavior . . .
•Because the DLS (the region thought to be involved in
Stimulus-Response learning) had a lesion and was nonfunctional, the habit of lever pressing did not seem to be
consolidated in these rats.
•After the value of the reward had been reduced and the rats
were later tested for extinction, control rats pressed the levers at
a higher rate than the rats with lesions to the DLS.
•It appears as if lever pressing had become a habit for the
controls.
•It seems that when the Stimulus-Response type of learning
cannot be performed by the DLS, the Action-Outcome type of
learning compensates for this by becoming the primary type of
learning to occur.
. . . However, a similar effect was not observed in rats with
DMS lesions
•In this case, the DMS (the region thought to be involved in
Action-Outcome learning) had a lesion and was nonfunctional.
•Contrary to the previous experiment, it appears that the
Stimulus-Response type of learning is unable to compensate
for the lack of Action-Outcome learning whenever the
structures responsible for Action-Outcome learning are
damaged.