Computational Analysis of Motor Learning

Three paradigms Force field adaptation Visuomotor transformations Sequence learning Does one term (motor learning) fit all? How to determine similarities/differences? Acquisition: On-line vs. KR feedback Generalization: Transfer

Motor Learning Three paradigms Force field adaptation Visuomotor transformations Sequence learning Does one term (motor learning) fit all? Neural systems: Do these tasks engage common regions?

Motor Learning Three paradigms Force field adaptation Visuomotor transformations Sequence learning Does one term (motor learning) fit all? Neural systems: Do these tasks engage common regions? Test case: Cerebellum

Smith and Shadmehr, 2005 Force field adaptation is impaired in patients with cerebellar degeneration and not basal ganglia degeneration.

Prism adaptation impairment in patient with bilateral cerebellar stroke. Control Participant Cerebellar Stroke Martin et al., 1996

Gomez-Beldarrain et al., 1998 Sequence learning is absent (ipsilesional) in patients with unilateral cerebellar stroke. S S S R S S S R

Classical conditioning of eyeblink response

Cerebellar lesions selectively abolish the learned response. McCormick et al., 1984; many others

Model system of motor learning 1.Dissociation of performance and learning. 2.Many species. 3.Specification of US and CS pathways. -- US, CS simulations. -- Reversible lesions 4.Genetic manipulations.

Cerebellar lesions selectively abolish the learned response. But not all forms of classical conditioning. McCormick et al., 1984; many others Pre-training lesions

Specifying domain of function. Task domain: Cerebellum for motor learning. Computation: Cerebellum for learning precise timing between stimulus events.

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.

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

Multiple levels of learning. Simple associations at DCN Precise timing from cerebellar cortex to flexibly make response adaptive.

Motor Learning Three paradigms Force field adaptation Visuomotor transformations Sequence learning Neural systems: Do these tasks engage common regions? Revisit role of cerebellum: Do these tasks require precise timing?

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.

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. Stimuli, responses lack precise timing. Transfer indicates effector-independent learning. Computational analysis: Cerebellum not essential for sequence learning.

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.

Patient GroupsDegree of Learning Compared to Controls Normal Attenuated None Basal ganglia Parkinson’s:2 41 Focal BG lesions2 10 Cerebellum0 15

Patient GroupsDegree of Learning Compared to Controls Normal Attenuated None Basal ganglia Parkinson’s:2 41 Focal BG lesions2 10 Cerebellum0 15 Imaging results Directional Change in Activation with Learning Increases No Change Decreases Basal Ganglia5 60 Cerebellum0 64

Patient GroupsDegree of Learning Compared to Controls Normal Attenuated None Basal ganglia Parkinson’s:2 41 Focal BG lesions2 10 Cerebellum0 15 Imaging results Directional Change in Activation with Learning Increases No Change Decreases Basal Ganglia5 60 Cerebellum0 64 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?

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.

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 locationwith central color Successive targets follow 8-element sequence or selected randomly. Symbolic cues tax S-R coding system (e.g., Wise premotor)

Patients selectively impaired with symbolic cues. Consistent with performance problem rather than sequence learning per se.

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.

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

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. Directional Change in Activation with Learning Increases No Change Decreases SRT learning0 64

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. Directional Change in Activation with Learning Increases No Change Decreases SRT learning0 64 Prediction: Weak cerebellar/prefrontal activation with direct cues.

Motor Learning Cerebellar role in learning Sequence learningIndirect (no timing) Force field adaptationlikely (on-line timed error signal) Visuomotor transformations???

Motor Learning Cerebellar role in learning Sequence learningIndirect (no timing) Force field adaptationlikely (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

Motor Learning Cerebellar role in learning Sequence learningIndirect (no timing) Force field adaptationlikely (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?

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.

“Constant” somatosensory input that is either expected or unexpected Unexp. Exp. Unexp

Exp Unexp

Errors of Omission and Commission Actual Yes No ExpectedYesCorrectOmission NoCommissionCorrect Errors of commission are well-timed. Errors of omission lack precise timing.