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


Descending Spinal Tracts

• Axons from brain descend along two major pathways

– Lateral Pathways

– Ventromedial Pathways



• The Lateral Pathways

– Voluntary movement originates in cortex

– Components

• Corticospinal tract

(pyramidal tract)

• Rubrospinal tract



• 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



• The Ventromedial Pathways

– Posture and locomotion originates in brain stem

• The Vestibulospinal tract

: head balance, head turning

• The Tectospinal tract: orienting response



• The Ventromedial Pathways

– The Pontine and Medullary

Recticulospinal

Recticulospinal tract

• Pontine: enhances antigravity reflexes

• Medullary: liberates antigravity muscles from reflex



• Summary


The Planning of Movement by the Cerebral

Cortex

• Motor Cortex

– Area 4 and area 6 of the frontal lobe



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



Cortex

• Motor Cortex

– Somatotopic organization of precentral gyrus (like postcentral gyrus)



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



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


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


The Basal Ganglia

• Basal Ganglia: Selection and initiation of willed movements



• Basal ganglia

– Project to the ventral lateral (VLo) nucleus

– Provides major input to area 6

• Cortex

– Projects back to basal ganglia

– Forms a “loop”



• 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



• 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



• 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


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



Motor Cortex

• Coding Movement in M1

– Recordings from a single cell in M1 illustrating

“direction vector”



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)



Motor Cortex

• Coding Movement in

M1(Cont’d)

– Population Vectors


Control of saccadic eye movements by the

Superior Colliculus

• Computational map of Motor ‘error’

• Motor error : Desired eye position – current eye position

30

Up

20

10

Left superior colliculus

2 º

B

5

10

B



C

A  B X 

A

A

C 20

10

Right

20 30

30

-40

-20

(Down)

-10 0 º

+10

+20

(Up)

+40



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


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


The Cerebellum

• Anatomy of the Cerebellum


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


The Cerebellum

• The Motor Loop Through the Lateral Cerebellum

– Calibrated execution of planned, voluntary, multijoint movements


The 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


The Cerebellum


– Cerebellum- “brain inside”

• Learning

• New motor programs created to ensure smooth movement


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


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


End of Presentation


Chapter 14: Brain Control of Movement

Control of saccadic eye movements by the

Superior Colliculus

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Control of saccadic eye movements by the

Superior Colliculus

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