Describe the theory of cortical reorganisation PDF

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Describe the theory of cortical reorganisation, and make a persuasive argument that it can explain phantom pain

Cortical reorganisation, or otherwise known as cortical remapping, is the process where an existing cortical map is affected by a stimulus creating a ‘new’ cortical map. Cortical reorganisation is not only altered by injury but also training and stimulation related to behaviour (Flor 2003). The idea of cortical reorganisation is that each body region has its own corresponding cortical neurons topographically mapped, from the body through to the thalamus and the sensory cortex. When disruption occurs in the cortical maps, example amputation or deafferentation, it results in a decrease of input to sensorimotor cortices and thus diminishes cortical representation. The portion of the brain in charge of the amputation or neuron activity will be dominated by the adjacent cortical regions which receives stimulus, therefore establishing a remapped system. Clinical manifestations resulted from this include phantom limb sensations and phantom limb pain (MacIver et al 2008 ). The purpose of this is so affected individuals can regain function from injury.

Phantom limb describes the phenomena of experiencing sensations in a missing body part. Estimated that 60-70% that undergone amputation experience phantom pain in the amputated limb (Sherman et al 1984). Tim Pons revealed that the primary somatosensory cortex in monkeys underwent substantial reorganisation after loss of sensory input. Pons touched the part related to the affected region and noted no activity occurring. Though, when the monkey’s face was stroked, it showed that neurons corresponding to the amputated region was actively firing (Phantom Limb Syndrome). This demonstrates that sensory neuronic information from the monkey’s face occupied the cortex of the amputated hand, thus suggesting phantom pain is correlated to cortex reorganisation and caused in phantom pain to occur. One way of proving cortical reorganisation as an explanation for phantom pain is the use of magnetoencephalography (MEG). It is a non-invasive technique which reads magnetic fields produced by neuronic activity in the brain (Hämäläinen et al., 1993). The use of MEG produces maps which can identify cortical regions that demonstrates sensory input. In a study done by Ramachandran, he discovered that sensory information from the face and the arms invaded the hand region on the somatosensory map on four limb amputated individuals (Yang et al). Results from these MEG studies indicated that after reorganisation has occurred, the sensory information in the

face has been fired to the current cortical area as well as the previous cortical area, thus depicting phantom pain. Functional magnetic resonance imaging (fMRI) has substantial connections between phantom limb and cortical reorganisation. fMRI can recognize oxygenation in blood flow found in certain parts in the brain. In a research conducted by Maclver, thirteen patients with upper limb amputations were in a six-week investigation for activation during lip and hand movement. After investigation, individuals noticed a decline in the intensity and hostility of pain, corresponding to suppression of cortical reorganisation (MacIver et al., 2008). Patients with strokes also undergo cortical reorganisation for recovery. The mechanisms for recovery are based on structural and functional changes in brain circuits which have close functional relation to the circuits disturbed by stroke (Murphy 2009). In conclusion, cortical reorganisation is a major reason as to why patients feel phantom pain, since many body parts share close functional relations to each other, hence if one part of the body is hindered, an adjacent correlating region will merge and cause phantom pain.

References (i)

Flor H. Cortical reorganisation and chronic pain: implications for rehabilitation. J Rehabil Med. 2003 May;(41 Suppl):66-72. doi: 10.1080/16501960310010179. PMID: 12817660.

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MacIver K, Lloyd DM, Kelly S, Roberts N, Nurmikko T. Phantom limb pain, cortical reorganization and the therapeutic effect of mental imagery. Brain. 2008 Aug;131(Pt 8):2181-91. doi: 10.1093/brain/awn124. Epub 2008 Jun 20.

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Sherman RA, Sherman CJ, Parker L. Chronic phantom and stump pain among American veterans: results of a survey. Pain. 1984 Jan;18(1):83-95. doi: 10.1016/03043959(84)90128-3. PMID: 6709380.

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All Answers Ltd. (November 2018). Is Cortical Reorganisation a Strong Explanation of Phantom Limb Syndrome?. Retrieved from https://nursinganswers.net/essays/is-corticalreorganisation-a-strong-explanation-of-phantom-limb-syndrome.php?vref=1

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Hämäläinen, M., Hari, R., Ilmoniemi, R., Knuutila, J. and Lounasmaa, O. (1993).

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MacIver, K., Lloyd, D., Kelly, S., Roberts, N. and Nurmikko, T. (2008). Phantom limb pain, cortical reorganization and the therapeutic effect of mental imagery. Brain, 131(8), pp.2181-2191.

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Murphy TH, Corbett D. Plasticity during stroke recovery: from synapse to behaviour. Nat Rev Neurosci. 2009 Dec;10(12):861-72. doi: 10.1038/nrn2735. Epub 2009 Nov 4. PMID: 19888284.

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