Motor Events

Dr Christian Thode

MAKE NOTES ON THE FIRST TWO WEEKS OF CHRISTIAN THODES LECTURES “ VERTEBRATE BRAIN

Overview

Motor Events:

• Neuronal Programmes

  • animal models

  • feedback loops

• Planning movement

  • role of the cortex

  • role of the basal ganglia

  • role of the cerebellum

Planning & Control of Movement

Comparison - Hierarchy of Regions

Song Learning in the Zebra Finch

• Birdsong, like human speech, is a motor behaviour. It is learned progressively in two phases:

  • sensory – the bird is exposed to a tutor’s song, and stores this as long-term memory

  • sensorimotor – the juvenile bird forms its own vocalisations

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The Avian Song System

• It consists of two interconnected neuronal circuits.

• The motor pathway innervates the vocal organ (syrinx); it is required for song production. The connected Field L provides information on the bird’s own song.

• The anterior forebrain pathway is involved in song learning and maintenance; it forms a feedback loop to the vocal motor pathway.

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Feedback Loops

• During singing, the desired and the actual movement are compared and corrections are made – feedback loops involve different parts of the brain.

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Motor Cortex

• The primary motor cortex (area 4 or M1) is located in front of the central sulcus, next to the somatosensory cortex (S1).

• The regions of area 6, the supplementary motor area and premotor area, also contribute to movements.

  • → area 4 – simple movement

  • area 6 – complex movements

  • → Wilder Penfield;

  • contralateral activation

  • ⇒ somatotopic organisation

• → Wilder Penfield;

  contralateral activation

  ⇒ somatotopic organisation

Somatotopic Map (Motor Cortex)

Motor Cortex

• Key contributions come from the posterior parietal cortex, which receives information from the primary sensory cortex and visual cortex.

• The parietal cortex is connected to the prefrontal cortex (abstract thought, decisions, prediction of consequences).

• Both areas are at the highest level in the hierarchy of motor control.

  • → send axons to area 6 to code for what actions will take place ⇒ corticospinal tract

• PET scans light up areas 4, 6 and 8 (prefrontal) when actions are performed from memory.

Basal Ganglia

Basal Ganglia Motor Loop

• The basal ganglia themselves receive input from the frontal, prefrontal and parietal cortex (⇒ motor loop).

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Direct Connections

• The motor loop involves the excitation of inhibitory neurons (putamen) that inhibit inhibitory neurons (globus pallidus).

  • → cells in the globus pallidus are spontaneously active

  • ⇒ inhibition there results in excitation of the SMA

• The SMA is interconnected with area 4 and stimulates cells there to produce movement in the correct direction and time.

  • ⇒ initiation of voluntary movements

Direct & Indirect Connections

Basal Ganglia & Parkinson’s Disease

Motor Loop in Parkinson’s Disease

Cerebellum

• The cerebellum (Cb) is important for the co-ordination and accuracy of motor activities.

  • → monitors and corrects

  • → integrates information from the vestibular apparatus and proprioceptors

  • → predicts movements

• These regulating effects are [not] noticeable after alcohol consumption.

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Inputs to Cerebellum

Outputs from the Cerebellum

Summary of Motor Loops