Bear Neuroscience Exploring the Brain 3 e Chapter

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 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Descending Spinal Tracts • Axons from brain descend along two major pathways – Lateral

Descending Spinal Tracts • The Lateral Pathways – Voluntary movement originates in cortex – Components • Corticospinal tract (pyramidal tract) • Rubrospinal tract Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

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 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

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 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Descending Spinal Tracts • The Ventromedial Pathways – The Pontine and Medullary Recticulospinal tract • Pontine: enhances antigravity reflexes • Medullary: liberates antigravity muscles from reflex Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Descending Spinal Tracts • Summary Copyright © 2007 Wolters Kluwer Health | Lippincott Williams

The Planning of Movement by the Cerebral Cortex • Motor Cortex – Area 4

The Planning of Movement by the Cerebral Cortex • Motor Cortex (Penfield) – Area 4 = “Primary motor cortex” or “M 1” – 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 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

The Planning of Movement by the Cerebral Cortex • Motor Cortex – Somatotopic organization of precentral gyrus (like postcentral gyrus) Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

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 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

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 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

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 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

The Basal Ganglia • Basal Ganglia: Selection and initiation of willed movements Copyright ©

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” Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

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 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

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 jaw • Organic basis: Degeneration of dopaminergic substantia nigra inputs to striatum • Dopa treatment: Facilitates production of dopamine to increase SMA activity Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

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 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Initiation of Movement by the Primary Motor Cortex • Electrical stimulation of area 4 – Contraction of small group of muscles • The Input-Output Organization of M 1 – Betz cells: Pyramidal cells in cortical layer 5 – Two sources of input to Betz cells • Cortical areas • Thalamus • Coding Movement in M 1 – Activity from several neurons in M 1 encodes force and direction of movement Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Initiation of Movement by the Primary Motor Cortex • Coding Movement in M 1 – Recordings from a single cell in M 1 illustrating “direction vector” Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Initiation of Movement by the Primary Motor Cortex • Coding Movement in M 1(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) Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

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 10 C 10 20 30 Right Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins A B X A

Initiation of Movement by the Primary Motor Cortex • The Malleable Motor Map: Experimental rats – Microstimulation of M 1 cortex normally elicits whisker movement – Cut nerve that supplies whisker muscles – Microstimulation now causes forelimb movement Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

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 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

The Cerebellum • Anatomy of the Cerebellum Copyright © 2007 Wolters Kluwer Health |

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 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

The Cerebellum • The Motor Loop Through the Lateral Cerebellum – Calibrated execution of

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 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

The Cerebellum • The Motor Loop Through the Lateral Cerebellum – Cerebellum- “brain inside” • Learning • New motor programs created to ensure smooth movement Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

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 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Concluding Remarks • Example of the baseball pitcher (Cont’d) – Winds and throws • Increased basal ganglia activity (initiation) • SMA activity M 1 activation • Corticopontocerebellar pathways Cerebellum • Cortical input to reticular formation Release of antigravity muscles • Lateral pathway engages motor neurons action Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins