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PLASTICITY AFTER INJURY (INFLUENCING FACTORS (Lesion size: controversial,…
PLASTICITY AFTER INJURY
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INFLUENCING FACTORS
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Location of the lesion: subcortical regions produce greater impairment due to less plastic mechanisms (e.g. redundancy of circuitry)
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PHANTOM LIMB
Reorganization of topography. After amputation of an arm, sensory input from the face begins to activate the hand area of the Penfield homunculus in cortical area S1.
Remapping theory of referred sensations: referred sensation emerge as a direct consequence of the changes in topography following differentiation
Experiments with phantom limb patients are used to explain brain plasticity. Why? Because topography is extremely labile so even in the adult brain massive reorganization can occur over extremely short periods
Phantom pain: some patients experience excruciatingly painful involuntary clenching spasms in the phantom limb; the experience their limbs digging into their phantom palm and are unable to open the hand voluntarily to relieve the pain
Mirror Therapy
Contradiction: since nothing is seen or felt other than the pain, there is nothing directly contradicting it; when the patient looks at the visual reflection of the real hand, however, he sees that there is not external object causing the pain so his brain rejects the pain signal as spurious (not formally studied)
Discrepancy: phantom pain is – at least in part – a response to the discrepancy between different senses such as vision and proprioception (opposition: not every discrepancy leads to pain)
Neuromechanism: it might be that when you watch someone being touched, even though your ‘touch mirror neurons’ are activated the receptors in your skin are not stimulated and this lack of activity (the ‘null signal’) informs your regular garden variety touch neurons (i.e. non-mirror touch neurons) that your hand is not being touched --> they in turn partially veto the output of mirror touch neurons at some later stage so you do not actually experience touch sensations