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11-03-2013 | Pain medicine | Article

Phantom limb pain linked to preserved structure and function in the former hand area

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medwireNews: Amputee phantom pain is associated with strong representations of the missing limb in the brain, show study results.

The researchers hope that these findings could aid the development of treatment approaches, as well as increase understanding of how the brain reorganizes and adapts to new situations.

Previous studies have suggested that phantom pain after arm amputation arises from maladaptive cortical reorganization, triggered by loss of sensory input.

In the present investigation, Tamar Makin, from the University of Oxford in the UK, and colleagues used magnetic resonance imaging (MRI) to study how phantom limb pain felt by people who have had an arm amputated is related to changes in the brain.

The team studied 18 individuals with unilateral upper-limb amputation (amputees), 11 individuals with a congenital unilateral upper-limb deficiency and no phantom sensations (one-handers), and 22 individuals with two full upper limbs (two-handers).

All participants underwent a functional MRI scan while moving each hand separately. Amputees were instructed to "move" their phantom limb and one-handers were instructed to imagine moving their missing hand, as they did not have phantom limbs.

As reported in Nature Communications, Makin and co-investigators observed comparable patterns of movement-related activity when amputees moved their phantom hand compared with two-handed controls moving their non-dominant hand.

The extent to which the amputees maintained the representation of their missing hand was linked to the strength and frequency of the pain the amputees felt; those feeling the greatest pain retained the strongest representations.

The amount of gray matter in the area of the brain representing the phantom hand was reduced in amputees compared with those with two hands. This was also linked to the amount of pain amputees felt; those experiencing stronger pain showed less structural degeneration in the missing hand area following the loss of the limb.

In a press statement, Makin said: "Most people experience 'phantom' sensations in a missing limb after amputation. This disconnect between the physical world and what they are experiencing appears to be linked to a functional detachment in the brain. There seem to be reduced connections between the missing limb part of the brain and the rest of the cortex that's involved in movement."

He concluded: "Our results may encourage rehabilitation approaches that aim to recouple the representation of the phantom hand with the external sensory environment."

By Nikki Withers, medwireNews Reporter

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