Transplanted hands regain representation in motor and somatosensory cortex

In Figure 8.11 (b and c), we saw that when a finger is denervated or lost, adjacent intact parts of the hand take over its representation in somatosensory cortex. When a hand is lost, the cortical regions that represent the upper arm and face expand, taking over the cortical area that previously represented the missing hand (Figure 8.12). Similar changes occur in the motor cortex after loss of a hand.

Recent research shows a reciprocal phenomenon: when hands are transplanted to a patient, there is cortical reorganization that gives the new hands apparently normal representation in primary motor cortex (M1) and primary somatosensory cortex (S1).

Over the last few years, a number of cases have been reported in which a severed hand has been surgically reattached or in which a hand has been transplanted. In 2000 the first double hand transplant was reported, and representation of the hand in the cortex was studied both preoperatively and postoperatively with fMRI recordings (Giraux et al., 2001). The patient, D.C., lost his hands in 1996 when a home-made model rocket exploded. The transplant operations were performed in 2000 in Lyons, France by a 50-member surgical team. Similar fMRI recording sessions were made 6 months before the grafts and 2, 4, and 6 months afterwards.

In each session, the patient was instructed to (1) flex and extend the last four digits of the right hand, (2) flex and extend the right elbow, (3) flex and extend the last four digits of the left hand, and (4) flex and extend the left elbow. The instructions were to really try to execute the movements and not just to imagine them (personal communication from A. Sirigu, August 31, 2001). To make sure that C.D. was trying to move the fingers, the investigators monitored the movements of the muscles in the forearm that control movements of the fingers; this was done both before and after the transplants.

Before the operation, attempted movements of the hand activated only the most lateral part of the normal hand area in M1, adjacent to the face area (see Figure 11.13). During the six postoperative months, the area of cortex activated by hand movements expanded to occupy the entire normal hand region. Before surgery, much of the hand region was activated by movement of the elbow; during recovery, representation of the elbow moved back to the classical arm area. Similar changes of sensory hand representation were observed in S1. So the reorganization of the cortex occurred in an orderly way. Some expansion of the hand region was observed at 2 and 4 months postoperatively, although at that time C.D. could barely move his transplanted hands.

C.D. has continued to regain sensitivity and control of his hands. He can localize stimuli on his hands, and he can modulate movements. Although he does not have much strength in his hands, he can perform such tasks as picking up a comb and combing himself. A case of a double hand transplant in Austria in 2000 with satisfactory recovery was reported in the press (BBC News Online, 2000). The patient was a policeman who lost his hands in 1996 in a terrorist explosion. Although brain recordings were not undertaken in the Austrian case, the recovery of motor and sensory functions indicates brain plasticity. These cases show plasticity of both motor and somatosensory cortex in adult humans.

References:

BBC News Online (September 4, 2000). Hand transplant man 'ready for work.'

Giraux, P., Sirigu, A., Schneider, F. and Dubenard, J.-M. (2001). Cortical reorganization in motor cortex after graft of both hands. Nature Neuroscience, 4:7, 691-692.