Brain Advance Access originally published online on July 14, 2006
Brain 2006 129(8):2202-2210; doi:10.1093/brain/awl180
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Mapping phantom movement representations in the motor cortex of amputees
1 Institut des Sciences Cognitives, CNRS Bron, France 2 Université Claude Bernard Lyon1 Lyon, France 3 Department of Neurobiology and Anatomy, University of Rochester Rochester, NY, USA 4 IBCCF, UFRJ Rio de Janeiro, Brazil
Correspondence to: Dr Angela Sirigu, Institut des Sciences Cognitives, CNRS, 67, Boulevard Pinel, 69675 Bron, France E-mail: sirigu{at}isc.cnrs.fr
Limb amputation results in plasticity of connections between the brain and muscles, with the cortical motor representation of the missing limb seemingly shrinking, to the presumed benefit of remaining body parts that have cortical representations adjacent to the now-missing limb. Surprisingly, the corresponding perceptual representation does not suffer a similar fate but instead persists as a phantom limb endowed with sensory and motor qualities. How can cortical reorganization after amputation be reconciled with the maintenance of a motor representation of the phantom limb in the brain? In an attempt to answer this question we explored the relationship between the cortical representation of the remaining arm muscles and that of phantom movements. Using transcranial magnetic stimulation (TMS) we systematically mapped phantom movement perceptions while simultaneously recording stump muscle activity in three above-elbow amputees. TMS elicited sensations of movement in the phantom hand when applied over the presumed hand area of the motor cortex. In one subject the amplitude of the perceived movement was positively correlated with the intensity of stimulation. Interestingly, phantom limb movements that the patient could not produce voluntarily were easily triggered by TMS, suggesting that the inability to voluntarily move the phantom is not equivalent to a loss of the corresponding movement representation. We suggest that hand movement representations survive in the reorganized motor area of amputees even when these cannot be directly accessed. The activation of these representations is probably necessary for the experience of phantom movement.
Key Words: amputation; phantom limb; transcranial magnetic stimulation; motor cortex; movement
Abbreviations: MEP, motor-evoked potential; TMS, transcranial magnetic stimulation
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Received January 17, 2006. Revised June 8, 2006. Accepted June 9, 2006.
5Present address: Centre Interdisciplinaire de Recherche en Réadaptation et Intégration Sociale, Québec, Canada
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