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Motor cortex

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Physiology 3120
Tom Stavraky

Human Physiology Monday, November 16, 2009 “Neuro XI” Motor Cortex • Techniques used to study function of particular brain region 1. Stimulation  Electrical  Magnetic: rapidly changing magnetic fields can induce currents in cortex)  Epilepsy (natural) 2. Lesion  Electrical  Chemical  Stroke, degeneration (natural) 3. Recording  Single neurons  Evoked potentials & EEG (observe populations of neurons)  PET scan & fMRI (record differences in blood flow to brain regions • Motor cortex  Region from which low intensity stimulation elicits muscle contractions  Precentral gyrus (i.e. just anterior to central sulcus)  Usually evoked flexion movement at a joint; elicit jerk-like movement because we elicit large numbers of neurons that don’t normally fire together  Movement is contralateral of stimulation • Somatotopic organization  Equivalent to somatotopic organization of somatosensory cortex  Larger representations for the fingers & the face; therefore, there is a bigger area from which we can produce finger movement  Represents a distorted homunculus with larger representations for fingers & face  Evidence  Hughlings Jackson found that epileptic motor seizures move from medial to lateral (i.e. Jacksonian March)  Wilder Penfield confirmed this hypothesis in stimulation studies  Lesions to either (I) paralysis, or (II) weakness • Organization is plastic  Laid down at birth, but modifiable by experience  Evidence  Experimental injury • Blocked small artery that supplied the hand area • Some monkeys were trained after damage, and some were not • The monkeys were trained or not; the monkeys that were trained to use their hand regained some hand function, and hand representation had relocated to adjacent area of cortex previously responsible for shoulders & elbows  Learning • When patients had to learn a keyboard sequence, there was an increase in finger representation in the motor cortex over several weeks
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