Cortical Control of Movement

1. Cortical Control of Movement Lecture 22

2. 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 ~

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

4. 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

7. Primary Motor Cortex Somatotopic organization neurons have preferred direction of movement Motor homunculus ~

8. 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 ~

9. M1: Coding Movement Implications 1. MostM1 active for every movement 2. Activity of each neuron 1 �vote� 3. direction determined by averaging all votes ~

10. 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 ~

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

12. 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 ~

13. 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 ~

14. The Descending Spinal Tracts

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

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

17. Spinal Cord: Lateral Pathway

18. 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 ~

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

20. 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 ~

21. 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 ~

22. Spinal Cord: Ventromedial Pathway

23. Major Descending Spinal Tracts

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