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

5. SMA M1
PPC S1 PM

6. Sensorimotor Pathwaysf o n t a l
SMA
PPC M1 S1 PM

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
Dorsal
Ventral
Corticospinal
tract
Cortico-
rubrospinal
tract

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
Dorsal
Ventral
Vestibulospinal
tract
Tectospinal
tract
Medullary
Reticulospinal
tract
Pontine
Reticulospinal
tract

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

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