Sensorimotor Control of Behavior: Movement

1. Sensorimotor Control of Behavior: Movement Lecture 9

2. Motor Systems • Functions • movement • posture & balance • communication • Guided by sensory systems • internal representation of world & self • detect changes in environment • external & internal ~

3. Movement & Muscles • Movement occurs at joints • Contraction & relaxation of of opposing muscles • agonists • prime movers • antagonists • counterbalance agonists • decelerate movement ~

4. Dorsal + + - + Alpha Motor neurons Ventral Upper Motor Neurons +

5. Movement & Muscles • Movement control more than contraction & relaxation • Accurately time control of many muscles • Make postural adjustment during movement • Adjust for mechanical properties of joints & muscles • inertia, changing positions ~

6. 3 Classes of Movement • Voluntary • complex actions reading, writing, playing piano • purposeful, goal-oriented • learned • improve with practice ~

7. 3 Classes of Movement • Reflexes • involuntary, rapid, stereotyped eye-blink, coughing, knee jerk • graded control by eliciting stimulus ~

8. 3 Classes of Movement • Rhythmic motor patterns • combines voluntary & reflexive acts chewing, walking, running • initiation & termination voluntary • once initiated, repetitive & reflexive ~

9. Organization of Motor Control • Hierarchical & Parallel • Parallel • pathways active simultaneously • e.g. moving arm 1. muscles producing movement 2. postural adjustments during movement • Recovery of function after lesion • overlapping functions ~

10. Hierarchical Control of Movement • 3 levels of control • Cortex • Brainstem • Spinal cord (SC) • Division of responsibility • higher levels: general commands • spinal cord: complex & specific • Each receives sensory input • relevant to levels function ~

11. 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: activates a motor neurons • reflexes • rhythmic pattern generators ~

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

13. 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

14. SMA PPC M1 S1 PM

15. The Descending Spinal Tracts

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

17. The Lateral Pathway • Voluntary movement • distal limbs • 2 tracts • Corticospinal tract • about 1 million axons • Rubrospinal tract • small part of pathway ~

18. Dorsal Corticospinal tract Ventral Spinal Cord: Lateral Pathway Rubrospinal tract

19. Corticospinal tract • Motor cortex ---> spinal cord • uninterrupted axon • 2/3 of axons from motor cortex • 1/3 from somatosensory cortex • Decussates at medulla • Contralateral control movement ~

20. The Rubrospinal Tract • Motor Cortex ---> red nucleus • Red nucleus ---> spinal cord • inputs from motor cortex • bigger role in other mammalian species ~

21. 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 ~

22. 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 ~

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

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

25. Primary Motor Cortex Cortical Control of Movement • Somatotopic organization • neurons have preferred direction of movement • Motor homunculus ~

26. 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 ~

27. 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

28. Motor Association Cortex • Motor area other than M1 • secondary motor cortex (M2) • Premotor & Supplemental Motor Areas • Active during preparation for movement • Planning of movements • Stimulation - complex movements • motor programs ~

29. Supplementary Motor Area - SMA • Primarily midline cortex • Inputs from … • PPC • S1 • Bilateral output to M1 • to distal limbs ~

30. Premotor Area - PMA • Anterior to M1 • Input • primarily from PPC • reciprocal connections with SMA • Outputs to M1 • then proximal limbs ~

31. PPC SMA M1 S1 PMA Spinal cord

32. 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 ~

33. Simple finger flexion • only M1 activation

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

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

36. Sensorimotor Integration • Perceptual development • Active interaction required • environmental feedback important • Held & Hein (1950s) • kittens passively moved • depth perception deficits • & related responses, blinking, looming ~

37. Sensorimotor Integration • Sensory inputs guide movement • visual, auditory, tactile • location of objects in space • Proprioceptive & vestibular • position of our body • Critical for planning & refining movements ~

38. Generation of Rhythmic Motor Patterns

39. Central Pattern Generators • Half-center Model • alternating activity in flexor & extensor • Step-cycle has 2 phases • swing phase • foot off ground & flexing forward • stance phase • foot planted & leg extending • Each limb has own pattern generator ~

40. + + + + + + + + Half-center Model Flexor a Tonic input a Extensor

41. Rhythmic Patterns: Sensory Feedback • Not necessary for locomotion • but slower, less coordinated • Stumble correction reaction • during swing phase • tactile stimulus on dorsal foot ---> flexion • Reflex reversal • override during extension • flexion would cause collapse ~

42. Goal-directed Locomotion • Requires intact supraspinal systems • Coordination of antigravity muscles • Brainstem motor nuclei • modulation of contraction strength • Reticulo-, rubro-, corticospinal • Balance • Vestibulospinal tract (Ventromedial) • Also cortical & subcortical areas ~