Reorganization of human motor cortex after hand replantation

In 10 patients, reorganizational changes of the motor cortex contralateral to a replanted hand (MCreplant) were studied one to 14 years after complete traumatic amputation and consecutive successful replantation of the hand. The organizational state of MCreplant was assessed for the deafferentated a nd peripherally deefferentated hand-associated motor cortex and the adjacen t motor representation of the proximal arm. For this, response maps were es tablished for the first dorsal interosseus and biceps brachii muscle using focal transcranial magnetic stimulation (TMS) on a skull surface grid. Char acteristics of the maps were center of gravity (COG), number of effective s timulation sites, amplitude sum, and amplitudes and response threshold at t he optimal stimulation point. The COG is defined by the spatial distributio n of response amplitudes on the map and lies over the cortex region with th e most excitable corticospinal neurones supplying the recorded muscle. The COG of the biceps map in MCreplant was shifted laterally by 9.8 +/- 3.6 tur n (range 5.0-15.7 mm). The extension of the biceps map in MCreplant was inc reased and the responses were enlarged and had lowered thresholds. For the muscles of the replanted hand, the pattern of reorganization was different: Response amplitudes were enlarged but thresholds, COG, and area of the cor tical response map were normal. The different reorganizational phenomena ob served for the motor cortical areas supplying the replanted hand and the bi ceps brachii of the same arm may be influenced by a different extent of dea fferentation and by their different role in hand motor control.