Pathways for Motor Control and Learning

Spinal Cord: The stretch reflex Maintain stability

Spinal Cord: The stretch reflex Maintain stability But modifiable: State dependent e.g., gait, sharpshooter

Spinal Cord: The stretch reflex Maintain stability But modifiable: State dependent Movement as change between postural states.

Reflex-like behavior in the right anatomy…. Complex behavior

Central Pattern Generators Evolutionary Learning

Rapid modification of “ancient” CPG Choi and Bastian, 2007 Split-belt

Rapid modification of “ancient” CPG Choi and Bastian, 2007 Stance Phase Grey: Fast leg Black: Slow leg Context-specific adaptation

Rapid modification of “ancient” CPG Choi and Bastian, 2007 Split-belt Hybrid walking: One leg forward and one leg backward

Descending Signals: Extrapyramidal Pathways Integration of other sensory signals with spinal mechanisms.

Subcortical Characters: The Cerebellum Multisensory (and other) inputs Descending and ascending output

Striatum Globus Pallidus Subthalamic nucleus Substantia nigra Components of the Basal Ganglia Subcortical Characters: The Basal Ganglia

Anatomical features: Multisensory/associative input Complex internal circuitry Restricted output Replication of circuitry

Motor Cortex The Cortex: Primary Motor Cortex

Internal capsule Pyramidal Tract (corticospinal) 90% Crossed; 10% Uncrossed Project to motor neurons and spinal interneurons Origin in M1, premotor, postcentral

Premotor Cortex The Cortex: Secondary Motor Areas Supplementary Motor Area (SMA)

The Cortex: Association “Motor” Areas (take that vision chauvinists) Pre-SMA

Views on hierarchical organization 1. Degree of sensory integration Spinal mechanisms: Limited to somatosensory Cortex: Polysensory

Views on hierarchical organization 1. Degree of sensory integration Spinal mechanisms: Limited to somatosensory Cortex: Polysensory 2. Flexibility: Contextualization of Action Exploiting degrees of freedom

Views on hierarchical organization 1. Degree of sensory integration Spinal mechanisms: Limited to somatosensory Cortex: Polysensory 2. Flexibility: Contextualization of Action Exploiting degrees of freedom 3. Abstraction of control Goal > Action > Movement e.g., reaching for coffee cup

Views on hierarchical organization 1. Degree of sensory integration Spinal mechanisms: Limited to somatosensory Cortex: Polysensory 2. Flexibility: Contextualization of Action Exploiting degrees of freedom 3. Abstraction of control Goal > Action > Movement e.g., reaching for coffee cup 4. Other ???

Motor Learning Three paradigms: Force field learning A: Baseline (null field) B. Force Field C. Initial Perf. D. Late Perf. E. Generated forces, late F. After-effect in null field

Motor Learning Three paradigms: Force field learning Visuomotor transformations DEMO

Motor Learning Three paradigms: Force field learning Visuomotor transformations examples: displacements, rotations, inversions, reversals (mirror drawing), depth distortions

Motor Learning Three paradigms: Force field learning Visuomotor transformations Sequence learning Serial Reaction Time Task Press response key corresponding to stimulus position. Stimuli follow sequence or are chosen at random.

Motor Learning Three paradigms Force field adaptation Visuomotor transformations Sequence learning Does one term (motor learning) fit all? How to determine similarities/differences?

Motor Learning S&W’s (anti)definition: Adaptation vs. Skills Adaptation: Retuning of existing competence. “Regain capabilities in altered circumstances.” Skill: “Expansion of motor repertoire.” Force field: Adaptation Sequence learning: Skill Visuomotor transformation: ???

Acquisition: error type? on-line vs. knowledge of results sensory vs. symbolic? rate of learning?

Acquisition: error type? rate of learning? Generalization local or general? transfer? SRT is symmetric Force field is better right to left VMT may be better left to right (?)

Acquisition: error type? rate of learning? Generalization local or general? transfer? Consolidation: Stability over time? Does learning related task interfere with initial learning? Would this be characteristic of skill or adaptation?

Consolidation in force field learning: B1: Initial force field B2: Second force field, learning after delay (consolidation phase) Time-dependent consolidation. Always some interference from B2. Is “control” correct term? Note that in control, there is an intervening force field– the null field of everyday life.

Motor Learning Three paradigms Force field adaptation Visuomotor transformations Sequence learning Neural systems: Do these tasks engage common regions?