Brain Motor Control

Lesson 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

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”

*all votes NOT equal

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 ~

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 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

Motor Loops

Cortex Subcortex Cortex Spinal cord

Cerebellum coordination of movement

Basal Ganglia selection & initiation of voluntary

movements Parallel Processing ~

Motor Loop Through Cerebellum

Lateral cerebellumsimplest circuit

20 million axons Cortex pons & cerebellum

Prefrontal, Motor, PPC Pons & Cerebellum thalamus

VLc - ventrolateral nucleus VLc M1 lateral pathway ~

Prefrontal PPCM1M2

Pons, CerebellumVLc

Distal Limbs

Lateral CerebellarMotor Loop

Basal Ganglia

Caudate nucleus Putamen

Globus Pallidus Substantia Nigra Tegmentum

Control slow movements Using immediate sensory feedback ~

Striatum

Prefrontal PPCM1M2

BasalGanglia VLo

Distal Limbs

Basal GangliaMotor Loop

Parkinson’s Disease

1% of population Nigrostriatal pathway

Substantia nigra neurons die Progressive loss

Hypokinesia Rigidity Bradykinesia Akinesia ~

Striatum

--

SubstantiaNigra

+

VA/VL

SubthalamicNucleus

+

Cortex

+

XParkinson’s Disease

+

GPiGPe

-

--

DirectIndirect

Parkinson’s Disease: Treatment

Basal Ganglia - Cholinergic Substantia Nigra - Dopaminergic Drug Therapy

L-DOPA Pallidectomy Tissue transplants ~

Huntington’s Disease (Chorea) Rare Genetic disorder

Single dominant gene, chrom. 4 onset 30-40s

Progressive disease Uncontrollable, jerky movements Dementia

Degeneration of Striatum Caudate & Putamen

GABA & ACh neurons ~

Striatum

--

SubstantiaNigra

+

VA/VL

SubthalamicNucleus

+

Cortex

+

XHuntington’s Disease

+

GPiGPe

-

--

DirectIndirect

HD gene huntingtin 3 forms

mutated form binds to protein involved in energy production neuron starves

Excitotoxicity contributes to degeneration glutamate Nitric oxide (NO) Potential treatment: Inhibit NO synthase ~

Huntington’s Disease: Cause