Cortical Control of Movement Lecture 22

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

SMA M1 PPC S1 PM

Sensorimotor Pathways f o n t a l SMA PPC M1 S1 PM

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. MostM1 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 secondary motor cortex (M2) Premotor & Supplemental Motor Areas Stimulation - complex movements motor programs Active during preparation for movement Planning of movements e.g. finger movements ~

Supplementary Motor Area - SMA Primarily midline cortex Input from PPC and prefrontal Bilateral output to M1 Distal & proximal limbs closing hand, orienting body ~

Premotor Area - PM Anterior to M1 Input primarily from PPC Reciprocal connections with SMA Outputs to M1 Proximal & axial muscles orienting body & arm to target ~

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) PM active before movement ~

The Descending Spinal Tracts

Brain to Spinal Cord Upper motor neurons communication with lower (a) motor neurons Lateral pathway direct cortical control Ventromedial pathway brain stem control ~

The Lateral Pathway Voluntary movement distal limbs 2 tracts Corticospinal tract about 1 million axons Cortico-rubrospinal tract facial muscles cranial nerves ~

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

Corticospinal tract Also called Pyramidal tract Motor cortex ---> spinal cord uninterrupted axon 2/3 of axons from motor cortex 1/3 from somatosensory cortex Decussates at medullary pyramids Contralateral control movement ~

The Cortico-rubrospinal Tract Motor Cortex ---> red nucleus Red nucleus ---> spinal cord inputs from motor cortex bigger role in other mammalian species ~

Lateral Pathway Damage Lesion both tracts no independent movement of distal limbs voluntary movements slow & less accurate Corticospinal only same deficits recovery over several months compensation by 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 ~

Spinal Cord: Ventromedial Pathway Dorsal Ventral Vestibulospinal tract Tectospinal tract Medullary Reticulospinal tract Pontine Reticulospinal tract

Major Descending Spinal Tracts Motor Cortex Lateral Ventromedial Reticular Nuclei Superior Colliculus vestibular nuclei Red Nucleus Spinal cord

Sensorimotor Integration Somatosensory cortex provides spatial coordinates Motor Cortex executes movements Results in meaningful behavior ~