Cortical Control of Movement

Lecture 20

Hierarchical Control of Movement

Association cortices & Basal Ganglia strategy : goals & planning based on integration of sensory info

Motor cortex & cerebellum tactics: activation of motor programs

Spinal cord execution: activation of alpha motor

neurons ~

Sensorimotor Cortical System

Integration of sensory information and directed movements

Anatomy Descending spinal tracts

Lateral pathway Pyramidal Motor System

Ventromedial pathway Extrapyramidal pathway ~

Cortical Anatomy S1 - postcentral gyrus PPC - Posterior Parietal Cortex M1 - Precentral Gyrus

Frontal Lobe somatotopic organization

M2 - Secondary Motor Cortex SMA - Supplementary Motor Area PM - Premotor Cortex ~

M1

SMA

S1

PM

PPC

M1 S1

PM

SMA

PPC

Prefrontal

Sensorimotor Pathways

Primary Motor Cortex

Somatotopic organization neurons have preferred direction of movement

Motor homunculus ~

M1: Coding Movement

Movement for limbs Neuron most active

Preferred direction but active at 45 from preferred

How is direction determined? Populations of M1 neurons Net activity of neurons with different

preferred directions vectors ~

M1: Coding Movement

Implications

1. Most M1 active for every movement

2. Activity of each neuron 1 “vote”

3. direction determined by averaging all votes ~

Motor Association Cortex Motor area other than M1

Premotor & Supplemental Motor Areas Active during preparation for movement

Planning of movements Stimulation - complex movements

motor programs Active during preparation for movement

Planning of movements e.g. finger movements ~

Motor Association Cortex Active before movement Supplemental Motor Area

Bilateral lesions unable to move or speak voluntarily

Some reflexive movement retained Premotor

Unilateral lesion impaired stability, gait, hand coordination

Fine motor control OK ~

M1 S1

PMA

SMA

Spinal cord

PPC

Planning Movements

Targeting vs trigger stimulus recording activity of neurons

active when movement planned for specific direction

Different populations of neurons active during planning (targeting) & execution (trigger stimulus) ~

Simple finger flexion only M1 activation

Sequence of complex finger movements M1 + SMA activation ~

Mental rehearsal of finger movements only SMA activation ~

The Descending Spinal Tracts

Brain to Spinal Cord

Upper motor neurons communication with lower () motor

neurons Lateral pathway

direct cortical control Ventromedial pathway

brain stem control ~

The Lateral Pathway

Voluntary movement distal limbs

Corticospinal (Pyramidal) tract Primary pathway (> 1 million neurons) Contralateral control movement

Cortico-rubrospinal tract Via red nucleus But some recovery if damage to

corticospinal ~

Dorsal

Ventral

Spinal Cord: Lateral Pathway

Corticospinal tract

Cortico-rubrospinal tract

The Ventromedial Pathway

Neurons originate in brainstem Vestibulospinal & tectospinal tracts

head & posture posture orienting responses

Pontine & medullary reticulospinal tracts originate in reticular formation trunk & antigravity leg muscles tracts are antagonistic ~

Major Descending Spinal Tracts

Motor Cortex

Spinal cord

Red Nucleus

Reticular Nuclei

Superior Colliculusvestibular nuclei

VentromedialLateral