Brain Motor Control Lesson 20

Hierarchical Control of Movement n Association cortices & Basal Ganglia l strategy : goals & planning l based on integration of sensory info n Motor cortex & cerebellum l tactics: activation of motor programs n Spinal cord l execution: activation of alpha motor neurons ~

Sensorimotor Cortical System n Integration of sensory information l and directed movements n Anatomy n Descending spinal tracts l Lateral pathway Pyramidal Motor System l Ventromedial pathway l Extrapyramidal pathway ~

Cortical Anatomy n S1 - postcentral gyrus n PPC - Posterior Parietal Cortex n M1 - Precentral Gyrus l Frontal Lobe l somatotopic organization n M2 - Secondary Motor Cortex l SMA - Supplementary Motor Area l PM - Premotor Cortex ~ M1 SMA S1 PM PPC

Primary Motor Cortex n Somatotopic organization l neurons have preferred direction of movement n Motor homunculus ~

M1: Coding Movement n Movement for limbs n Neuron most active l Preferred direction but active at 45  from preferred n How is direction determined? l Populations of M1 neurons l Net activity of neurons with different preferred directions l vectors ~

M1: Coding Movement n 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 n Motor area other than M1 l Premotor & Supplemental Motor Areas n Active during preparation for movement l Planning of movements n Stimulation - complex movements l motor programs n Active during preparation for movement l Planning of movements l e.g. finger movements ~

Planning Movements n Targeting vs trigger stimulus l recording activity of neurons n active when movement planned l for specific direction n Different populations of neurons active l during planning (targeting) l & execution (trigger stimulus) ~

n Simple finger flexion l only M1 activation n Sequence of complex finger movements l M1 + SMA activation ~ n Mental rehearsal of finger movements l only SMA activation ~

The Lateral Pathway n Voluntary movement l distal limbs n Corticospinal (Pyramidal) tract l Primary pathway (> 1 million neurons) l Contralateral control movement n Cortico-rubrospinal tract l Via red nucleus l But some recovery if damage to corticospinal ~

Dorsal Ventral Spinal Cord: Lateral Pathway Corticospinal tract Cortico- rubrospinal tract

Motor Loops n Cortex  Subcortex  Cortex  Spinal cord n Cerebellum l coordination of movement n Basal Ganglia l selection & initiation of voluntary movements n Parallel Processing ~

Motor Loop Through Cerebellum n Lateral cerebellum simplest circuit l 20 million axons n Cortex  pons & cerebellum l Prefrontal, Motor, PPC n Pons & Cerebellum  thalamus l VLc - ventrolateral nucleus n VLc  M1  lateral pathway ~

PrefrontalPPCM1M2 Pons, Cerebellum VLc Distal Limbs Lateral Cerebellar Motor Loop

Basal Ganglia n Caudate nucleus Putamen Globus Pallidus n Substantia Nigra l Tegmentum n Control slow movements l Using immediate sensory feedback ~ Striatum

PrefrontalPPCM1M2 Basal Ganglia VLo Distal Limbs Basal Ganglia Motor Loop

Parkinson’s Disease n 1% of population n Nigrostriatal pathway l Substantia nigra neurons die l Progressive loss n Hypokinesia l Rigidity l Bradykinesia l Akinesia ~

Striatum - - Substantia Nigra + VA/VL Subthalamic Nucleus + Cortex + X Parkinson’s Disease + GP i GP e Direct Indirect

Parkinson’s Disease: Treatment n Basal Ganglia - Cholinergic n Substantia Nigra - Dopaminergic n Drug Therapy l L-DOPA n Pallidectomy n Tissue transplants ~

Huntington’s Disease (Chorea) n Rare Genetic disorder l Single dominant gene, chrom. 4 l onset 30-40s n Progressive disease l Uncontrollable, jerky movements l Dementia n Degeneration of Striatum l Caudate & Putamen n  GABA & ACh neurons ~

Striatum - - Substantia Nigra + VA/VL Subthalamic Nucleus + Cortex + X Huntington’s Disease + GP i GP e Direct Indirect

n HD gene  huntingtin n 3 forms l mutated form binds to protein l involved in energy production l neuron starves n Excitotoxicity contributes to degeneration l glutamate  Nitric oxide (NO) l Potential treatment: Inhibit NO synthase ~ Huntington’s Disease: Cause