NROC64: Lec 8: Brain Control of Movement (nearly word-for-word what was said in lecture).docx

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14 Mar 2012
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NROC64: Lec 8: Brain Control of Movement
SAQ:
What is the inverse model?
ANSWER:
Cortical structures that convert a sensory intention or goal into a motor command. You need
info about what you need to do in order to achieve that sensory goal. Example of sensory goal
would be to have fovea look at next word while you’re reading. In our motor system, we have
knowledge about how to achieve that sensory goal (for the most part). Inverse model = convert
sensory goal into potential motor action that can be executed in order to achieve sensory goal
Slide 4: Introduction
brain influences activity of spinal cord
o voluntary movements (although sometimes unconscious and not controlled by
volition)
hierarchy of motor control:
o highest level = strategy
o middle level = tactics (planning the execution)
o lowest level = execution
also involves sensory system; sensorimotor system
o proprioception is critical for motor control
Slide 7: Descending spinal tracts
spinal cord at the bottom and there are several pathways that project onto spinal cord
o lateral pathways:
red nucleus (rubrospinal tract)
corticospinal tract
o ventromedial pathways
reticular nuclei
superior colliculus and vestibular nuclei
distinction from lateral and ventromedial come from when you transect thru spinal
cord, these sections are clearly separated and function separately
Slide 8: Lateral pathways
specifically involved in voluntary movement of distal muscles, esp flexors
components:
o corticospinal tract = pyramidal tract
starting point = cortico; end point = spinal ventral horn
decussation in spinal cord
o rubrospinal tract
starting point = red nucleus in midbrain = decussation happens here;
end point = spinal ventral horn
corticospinal tract is the more dominant lateral pathway in humans whereas rubrospinal
tract has lost most of its significance
lesions in lateral pathway may still allow individual to move effectors independently (like
your hand) but to move your fingers will be difficult
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3
Slide 12: Ventromedial pathways
posture and locomotion
mostly project to alpha motor neurons that innervate proximal and axial muscles
whereas lateral pathway is to distal muscles
under brainstem control
Vestibulospinal tracts:
o Projects from vestibular nuclei in medulla
o Innervates neck muscles in order to stabilize vision; when you’re walking,
without thinking you correct your head posture so that your eyes aren’t shaking
all the time
o Also involved in posture (to the legs); stretch reflex to prevent you from falling
Tectospinal tract:
o Projects from superior colliculus (tectum)
o Involved in orienting and attention
o Highly salient stimulus, turn your head towards it (often a combo of eye and
head movements) head for gaze movements
Pontine and Medullary reticulospinal tract:
o Antigravity reflexes
Slide 14: Lesions
Lesion of spinal cord affecting the alpha motor neurons:
o Lack of innervation of muscles themselves = paresis, paralysis
o Atrophy of muscles if no innervation
Lesion above the spinal cord (central lesions) produce opposite effects:
o At the beginning, when you get injury, may go thru spinal shock phase
(hypotonia, hemiplegia) = which is kind of similar to lesion of motor neurons of
spinal cord
o Hypertonia (muscles continuously contracted), hyperreflexia, Babinski (naturally
in babies, stretches out)
o Babinski in brain-damaged like in MS: lack of influence of brain onto alpha
motor neurons, then you get increase in certain reflexes
PLANNING OF MOVEMENT BY CEREBRAL CORTEX:
Slide 16: Cerebral cortex Motor Cortex
Area 4 (M1 = posterior portion of precentral gyrus next to central sulcus) and area 6 of
frontal lobe
Area 6 = premotor area; parts going into the fold are supplementary motor areas
Area S1 (= area 3) and areas 1 and 2 behind that are also involved in motor control with
direct projections
Area 5 which mainly gets inputs from somatosensory cortex
o Important in motor control
Area 7 which gets inputs from visual areas
o Important in motor control; eye movement control
Several areas involved in motor control; but then the entire brain is involved
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If you have plan for movement, then might be associated with premotor areas; if you
don’t have a plan for showing some sort of beh then may involve part of the prefrontal
cortex like areas involved in working memory, problem solving
Slide 17: Motor cortex (Penfield)
Area 6 = higher motor area (penfield)
o Lateral region premotor area (PMA)
o Medial region supplementary motor area (SMA); not just one area; eye
movement area is part of this
Motor maps in PMA and SMA
o Similar fxns; diff groups of muscles innervated **not correct even tho stated by
texted
o For ex, in premotor area = eye fields whereas SMA part = supplementary eye
movement areas same muscle groups but slightly diff fxns
o SMA and PMA DO subserve DIFFERENT FUNCTIONS
Slide 18: How SMA and PMA differ
Need to have some plan of converting sensory goal into a motor action; one component
of the inverse model will rely on cues that either come from outside world or from
inside (like memory)
These 2 are slightly diff processes and can see that for SMA = premotor area
o Histograms of APs recorded from one SMA cell
o Histograms of APs recroded from one PMA cell
Can see that the activity of the 2 cells in the diff regions is somewhat opposite
o For SMA cell, more activity is generated when movement is generated based on
INTERNAL cues (monkey making button presses based on memory)
o For PMA cell, opposite seen; when EXTERNAL cue, PMA fired more than when
internal cue
Beyond frontal cortex, also have parietal areas involved.
Slide 19: Contributions of posterior parietal and prefrontal cortex
Represent highest levels of motor control
o Decisions made about actions and their outcomes
Area 5 is posterior to S1; gets input from areas 3, 1 and 2
Area 7: gets input from higher-order visual cortical areas such as MT, visual info about
motion (dorsal stream)
o Not the site for lesions causing neglect; now we know that it’s more ventral
areas of the parietal cortex and temporal cortex lesions that are associated with
neglect
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Slide 20: Contributions of posterior parietal and prefrontal cortex
anterior frontal lobes: abstract thought, decision making and anticipating consequences
of action
Area 6: actions converted into signals specifying how actions will be performed
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