Download Chapter 14: Brain Control of Movement

Bear:
Neuroscience: Exploring the
Brain, 3e
Chapter 14: Brain Control of Movement
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins
Introduction
• The brain influences activity of the spinal cord
– Voluntary movements
• Hierarchy of controls
– Highest level: Strategy
– Middle level: Tactics
– Lowest level: Execution
• Sensorimotor system
– Sensory information used by all levels of the motor
system
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Descending Spinal Tracts
• Axons from brain descend along two major pathways
– Lateral Pathways
– Ventromedial Pathways
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Descending Spinal Tracts
• The Lateral Pathways
– Voluntary movement originates in cortex
– Components
• Corticospinal tract
(pyramidal tract)
• Rubrospinal tract
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Descending Spinal Tracts
• The Lateral Pathways (Cont’d)
– The Effects of Corticospinal Lesions
• Deficit in fractionated movement of arms and
hands
• Paralysis on contralateral side
• Recovery if rubrospinal tract intact
• Subsequent rubrospinal lesion reverses recovery
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Descending Spinal Tracts
• The Ventromedial Pathways
– Posture and locomotion originates in brain stem
• The Vestibulospinal tract
: head balance, head
turning
• The Tectospinal tract:
orienting response
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Descending Spinal Tracts
• The Ventromedial Pathways
–
The Pontine and Medullary
Recticulospinal
Recticulospinal tract
• Pontine: enhances
antigravity reflexes
• Medullary: liberates
antigravity muscles
from reflex
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Descending Spinal Tracts
• Summary
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The Planning of Movement by the Cerebral
Cortex
• Motor Cortex
– Area 4 and area 6 of the frontal lobe
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The Planning of Movement by the Cerebral
Cortex
• Motor Cortex (Penfield)
– Area 4 = “Primary motor cortex” or “M1”
– Area 6 = “Higher motor area” (Penfield)
• Lateral region  Premotor area (PMA)
• Medial region  Supplementary motor area (SMA)
• Motor maps in PMA and SMA
• Similar functions; different groups of muscles
innervated
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The Planning of Movement by the Cerebral
Cortex
• Motor Cortex
– Somatotopic organization of precentral gyrus (like
postcentral gyrus)
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The Planning of Movement by the Cerebral
Cortex
• The Contributions of Posterior Parietal and Prefrontal
Cortex
– Represent highest levels of motor control
• Decisions made about actions and their outcome
– Area 5: Inputs from areas 3, 1, and 2
– Area 7: Inputs from higher-order visual cortical areas
such as MT
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The Planning of Movement by the Cerebral
Cortex
• The Contributions of Posterior Parietal and Prefrontal
Cortex (Cont’d)
– Anterior frontal lobes: Abstract thought,
decision making and anticipating consequences
of action
– Area 6: Actions converted into signals specifying
how actions will be performed
– Per Roland Monitored cortical activation
accompanying voluntary movement (PET)
• Results supported view of higher order motor
planning
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The Contributions of Posterior Parietal
and Prefrontal Cortex
• Neuronal Correlates of Motor
Planning
–
Evarts:Demonstrated
importance of area 6 in
planning movement
• “ready”- Parietal and
frontal lobes
• “set”- Supplementary
and premotor areas
• “go”- Area 6
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The Basal Ganglia
• Basal Ganglia: Selection and initiation of willed
movements
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The Basal Ganglia
• Basal ganglia
– Project to the ventral
lateral (VLo) nucleus
– Provides major input
to area 6
• Cortex
– Projects back to basal
ganglia
– Forms a “loop”
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The Basal Ganglia
• The Motor Loop:
– Excitatory connection
from cortex to putamen
– Cortical activation
• Excites putamen
• Inhibits globus
pallidus
• Release VLo from
inhibition
– Activity in VLo influences
activity in SMA
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The Basal Ganglia
• The Motor Loop (Cont’d)
– Basal Ganglia Disorders
• Parkinson’s disease: Trouble initiating willed movements
due to increased inhibition of the thalamus by basal
ganglia
• Symptoms: Bradykinesia, akinesia, rigidity and
tremors of hand and jaw
• Organic basis: Degeneration of dopaminergic
substantia nigra inputs to striatum
• Dopa treatment: Facilitates production of dopamine
to increase SMA activity
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The Basal Ganglia
• The Motor Loop (Cont’d)
– Basal Ganglia Disorders (Cont’d)
• Huntington’s disease
• Symptoms: Hyperkinesia, dyskinesia, dementia,
impaired cognitive disability, personality
disorder
• Hemiballismus: Violent, flinging movement on
one side of the body
• Loss of inhibition with loss of neurons in
caudate, putamen, globus pallidus
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Initiation of Movement by the Primary
Motor Cortex
• Electrical stimulation of area 4
– Contraction of small group of muscles
• The Input-Output Organization of M1
– Betz cells: Pyramidal cells in cortical layer 5
– Two sources of input to Betz cells
• Cortical areas
• Thalamus
• Coding Movement in M1
– Activity from several neurons in M1 encodes force
and direction of movement
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Initiation of Movement by the Primary
Motor Cortex
• Coding Movement in M1
– Recordings from a single cell in M1 illustrating
“direction vector”
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Initiation of Movement by the Primary
Motor Cortex
• Coding Movement in M1(Cont’d)
– Movement of direction encoded by collective activity
of neurons
• Motor cortex: Many cells active for every
movement
• Activity of each cell: Represents a single “vote”
• Direction of movement: Determined by a tally (and
averaging)
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Initiation of Movement by the Primary
Motor Cortex
• Coding Movement in
M1(Cont’d)
– Population Vectors
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Control of saccadic eye movements by the
Superior Colliculus
• Computational map of Motor ‘error’
• Motor error : Desired eye position – current eye position
30
Left superior colliculus
Up
20
B
A
10
C
Horizontal (Right)
2º
5
AB XA
BC
10
20
30
10
20
30
-40
-20
-10
Right
(Down)
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0º
+10
+20
(Up)
+40
Initiation of Movement by the Primary
Motor Cortex
• The Malleable Motor Map:
Experimental rats
– Microstimulation of M1
cortex normally elicits
whisker movement
– Cut nerve that
supplies whisker
muscles
– Microstimulation now
causes forelimb
movement
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The Cerebellum
• Function: Sequence of muscle contractions; calibration
and coordination.
– Cerebellar lesions
• Ataxia: Uncoordinated and inaccurate movements
• Dysynergia: Decomposition of synergistic
multijoint movements
• Dysmetria: Overshoot or undershoot target
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The Cerebellum
• Anatomy of the Cerebellum
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The Cerebellum
• Anatomy of the Cerebellum (Cont’d)
– Folia and lobules
– Deep cerebellar nuclei: Cerebellar output
• Relay cerebellar cortical output to brain stem
structures
– Vermis: Axial musculature
• Contributes to ventromedial pathways
– Cerebellar hemispheres: limb movements
• Contributes to lateral pathways
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The Cerebellum
• The Motor Loop Through the Lateral Cerebellum
– Calibrated execution of planned, voluntary, multijoint
movements
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The Cerebellum
• The Motor Loop Through the Lateral Cerebellum
– Pontine nuclei
• Axons from layer V pyramidal cells in the
sensorimotor cortex form massive projections to
pons
– Corticopontocerebellar projection
• 20 times larger than pyramidal tract
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The Cerebellum
• The Motor Loop Through the Lateral Cerebellum
– Cerebellum- “brain inside”
• Learning
• New motor programs created to ensure smooth
movement
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Concluding Remarks
• Example of the baseball pitcher
– Walking: Ventromedial pathways
– Ready to pitch
• Neocortex, ventromedial pathways
– Pitch signs and strategy
• Sensory information engages parietal and
prefrontal cortex and area 6
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Concluding Remarks
• Example of the baseball pitcher (Cont’d)
– Winds and throws
• Increased basal ganglia activity (initiation)
• SMA activity  M1 activation
• Corticopontocerebellar pathways  Cerebellum
• Cortical input to reticular formation  Release of
antigravity muscles
• Lateral pathway  engages motor neurons 
action
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End of Presentation
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins