Cortical Control of Movement

1. Cortical Control of Movement Lecture 20

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. SMA M1 PPC S1 PM 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 ~

5. Sensorimotor Pathways SMA PPC P r e f r o n t a l M1 S1 PM

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

7. 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 ~

8. Implications 1. Most M1 active for every movement 2. Activity of each neuron 1 “vote” 3. direction determined by averaging all votes ~ M1: Coding Movement

9. 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 ~

10. Motor Association Cortex • Active before movement • Supplemental Motor Area • Bilateral lesions  unable to move or speak voluntarily • Some reflexive movement retained • Premotor • Unilateral lesion  impaired stability, gait, hand coordination • Fine motor control OK ~

11. SMA PPC M1 S1 PMA Spinal cord

12. 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) ~

13. Simple finger flexion • only M1 activation

14. Sequence of complex finger movements • M1 + SMA activation ~

15. Mental rehearsal of finger movements • only SMA activation ~

16. The Descending Spinal Tracts

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

18. 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 ~

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

20. 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 ~

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