THE MANY MANIFESTATIONS OF A CEREBELLAR TIMING SYSTEM

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Computational Analysis of Motor Learning
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Motor Learning Three paradigms Force field
adaptation Visuomotor transformations Se
quence learning Does one term (motor learning)
fit all? How to determine similarities/differen
ces? Acquisition On-line vs. KR
feedback Generalization Transfer
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Motor Learning Three paradigms Force field
adaptation Visuomotor transformations Se
quence learning Does one term (motor learning)
fit all? Neural systems Do these tasks engage
common regions?
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Motor Learning Three paradigms Force field
adaptation Visuomotor transformations Se
quence learning Does one term (motor learning)
fit all? Neural systems Do these tasks engage
common regions? Test case Cerebellum
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Force field adaptation is impaired in patients
with cerebellar degeneration and not basal
ganglia degeneration.
Smith and Shadmehr, 2005
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Prism adaptation impairment in patient with
bilateral cerebellar stroke.
Control Participant
Cerebellar Stroke
Martin et al., 1996
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Sequence learning is absent (ipsilesional) in
patients with unilateral cerebellar stroke.
S S S R S S S R
Gomez-Beldarrain et al., 1998
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Classical conditioning of eyeblink response
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Cerebellar lesions selectively abolish the
learned response.
McCormick et al., 1984 many others
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• Model system of motor learning
• Dissociation of performance and learning.
• Many species.
• Specification of US and CS pathways.
• -- US, CS simulations. -- Reversible
  lesions
• Genetic manipulations.

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Cerebellar lesions selectively abolish the
learned response. But not all forms of classical
conditioning.
Pre-training lesions
McCormick et al., 1984 many others
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Specifying domain of function. Task domain
Cerebellum for motor learning. Computation
Cerebellum for learning precise timing
between stimulus events.
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Specifying domain of function. Task domain
Cerebellum for motor learning. Computation
Cerebellum for learning precise timing
between stimulus events.
Timing hypothesis accounts for dissociation of
heart rate and eyeblink responses.
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Lesions of the cerebellar hemisphere do not
abolish eyeblink response but do disrupt the
adaptive timing.
Prelesion Postlesion
Trained with 200 ms ISI Trained with 500 ms ISI
Perrett et al., 1993
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Multiple levels of learning. Simple
associations at DCN Precise timing from
cerebellar cortex to flexibly make response
adaptive.
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Motor Learning Three paradigms Force field
adaptation Visuomotor transformations Se
quence learning Neural systems Do these tasks
engage common regions? Revisit role of
cerebellum Do these tasks require
precise timing?
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Sequence learning as test case.
Stimuli appear at one of four positions. Press
response key in corresponding position. Stimuli
follow sequence or are chosen at random.
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Sequence learning as test case.
Stimuli appear at one of four positions. Press
response key in corresponding position. Stimuli
follow sequence or are chosen at random.
Learning series of spatial associations. Stimu
li, responses lack precise timing. Transfer
indicates effector-independent learning. Computat
ional analysis Cerebellum not essential for
sequence learning.
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Avalanche of patient and imaging studies with SRT
task central question Is Structure X involved
in learning? Extensive focus on basal ganglia
and cerebellum given hypothesized role in skill,
procedural learning, and automaticity.
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Patient Groups Degree of Learning Compared to
Controls Normal Attenuated
None Basal ganglia Parkinsons 2
4 1 Focal BG lesions 2 1 0
Cerebellum 0 1 5
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Patient Groups Degree of Learning Compared to
Controls Normal Attenuated
None Basal ganglia Parkinsons 2
4 1 Focal BG lesions 2 1 0
Cerebellum 0 1 5 Imaging results
Directional Change in Activation with
Learning Increases No Change
Decreases Basal Ganglia 5
6 0 Cerebellum 0 6 4
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Patient Groups Degree of Learning Compared to
Controls Normal Attenuated
None Basal ganglia Parkinsons 2
4 1 Focal BG lesions 2 1 0
Cerebellum 0 1 5 Imaging results
Directional Change in Activation with
Learning Increases No Change
Decreases Basal Ganglia 5
6 0 Cerebellum 0 6 4
If both BG and Cerebellar lesions impair SRT
learning, why are imaging results so
different? If cerebellar lesions are so
devastating to learning, why decrease with
learning, esp. when motor cortical areas show
increase w/ learning?
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Sequence learning as test case. Performance-based
hypothesis
Cortical-cerebellar interactions to maintain S-R
mapping.
Non-cerebellar systems for forming sequential
associations.
Patient deficit Poor sequence learning because
noisy S-R codes provide weak input for
associative mechanisms.
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Prediction Deficit in SRT learning will be
reduced in patients with cerebellar lesions if
S-R coding requirements are minimized.
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Prediction Deficit in SRT learning will be
reduced in patients with cerebellar lesions if
S-R coding requirements are minimized.
Reach to target Reach to target associated
location with central color
Successive targets follow 8-element sequence or
selected randomly. Symbolic cues tax S-R coding
system (e.g., Wise premotor)
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Patients selectively impaired with symbolic
cues. Consistent with performance problem rather
than sequence learning per se.
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Experiment 2 Use more traditional
keypressing SRT task Compare with patient
control PD patients
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Experiment 2 Use more traditional
keypressing SRT task Compare with patient
control PD patients
Ataxia group shows selective impairment with
symbolic cues. Controls and PD learn with both
cues.
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Results bring together patient and imaging
work. Lesion All human cerebellar
studies have used symbolic cues. One monkey
lesion study used direct cues normal performance
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Results bring together patient and imaging
work. Lesion All human cerebellar
studies have used symbolic cues. One monkey
lesion study used direct cues normal
performance Imaging Consistent with imaging
studies showing reduction in cerebellar
activation over the course of learning. Demands
on maintaining S-R mapping will decrease over
time as mapping becomes well-learned. Directi
onal Change in Activation with Learning
Increases No Change Decreases SRT
learning 0 6 4
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Results bring together patient and imaging
work. Lesion All human cerebellar
studies have used symbolic cues. One monkey
lesion study used direct cues normal
performance Imaging Consistent with imaging
studies showing reduction in cerebellar
activation over the course of learning. Demands
on maintaining S-R mapping will decrease over
time as mapping becomes well-learned. Directi
onal Change in Activation with Learning
Increases No Change Decreases SRT
learning 0 6 4 Prediction Weak
cerebellar/prefrontal activation with direct cues.
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Motor Learning Cerebellar role in
learning Sequence learning Indirect (no
timing) Force field adaptation likely (on-line
timed error signal) Visuomotor
transformations ???
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Motor Learning Cerebellar role in
learning Sequence learning Indirect (no
timing) Force field adaptation likely (on-line
timed error signal) Visuomotor
transformations ??? Imaging and patient work
suggests yes. Working memory account Two
S-R maps required in transformed environment
S-R Map 1 Old Map S-R Map 2
Hypothesis of New Map
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Motor Learning Cerebellar role in
learning Sequence learning Indirect (no
timing) Force field adaptation likely (on-line
timed error signal) Visuomotor
transformations ??? Compare single- and
multi-step transformations. Single 25 deg
displacement in one step Multi 5 deg
every 20 trials
Predictions?
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Classic model of cerebellum and error detection
and correction. Parallel fibers Simple spikes
indicate context. Climbing fibers Complex
spikes indicate error. Complex spike activity
leads to weight change.
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Constant somatosensory input that is either
expected or unexpected
Unexp. Exp. Unexp
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Unexp. Exp. Unexp
Exp Unexp
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Errors of Omission and Commission
Actual Yes No Expected Yes Corre
ct Omission No Commission Correct Errors of
commission are well-timed. Errors of omission
lack precise timing.