A sensory map of the lost hand
A functional hand is essential, but a hand is not just a perfected gripping tool. It is an inherent part of our identity, of our relationship with the world and with others. A hand is irreplaceable: at the clinical level alone transplantation still presents too many risks and disadvantages. Göran Lundborg, a hand surgeon at the Malmö University Hospital (SE) and member of the SmartHand project, highlights something of a paradox: ‘The amputee would like to have an artificial hand but one which he experiences as an inherent part of his own body.’ In principle, it is possible to induce a sensitivity in the artificial hand by connecting a sensor located on the prosthesis to an electrode implanted directly into the somatosensory cortex or into the peripheral nervous system. But the specific nature of the relationship between a lost hand and the brain allows us to envisage another possibility. ‘The amputation of a hand causes considerable functional reorganisations of the sensorial cortex,’ explains Göran Lundborg. ‘One of the consequences of these reorganisations is the formation of a sensory map of the lost hand on the surface of the stump.’ Stimulation of a precise location on this map is felt by the amputee at the same place on his lost hand (see box). Is this then the way of giving the amputee the sensation of having an artificial hand that is very much his own? It is too soon to say. The first stage is to re-create the sensation of force exerted on the object gripped.
Will there be a map of sensors of the lost hand on the surface of the stump? if so,how?