Bear: Neuroscience: Exploring the Brain, 3e Chapter 14: Brain Control of Movement

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

Descending Spinal Tracts The Lateral Pathways Voluntary movement - originates in cortex Components Corticospinal tract (pyramidal tract) Rubrospinal tract

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

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

Descending Spinal Tracts The Ventromedial Pathways The Pontine and Medullary Recticulospinal Recticulospinal tract Pontine: enhances antigravity reflexes Medullary: liberates antigravity muscles from reflex

Descending Spinal Tracts Summary

The Planning of Movement by the Cerebral Cortex Motor Cortex Area 4 and area 6 of the frontal lobe

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

The Planning of Movement by the Cerebral Cortex Motor Cortex Somatotopic organization of precentral gyrus (like postcentral gyrus)

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

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

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

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”

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

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

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

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

Initiation of Movement by the Primary Motor Cortex Coding Movement in M1 Recordings from a single cell in M1 illustrating “direction vector”

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)

Initiation of Movement by the Primary 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 B BC AB XA A 10 C 10 20 30 Right

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

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 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

The Cerebellum The Motor Loop Through the Lateral 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