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