Reorganization of human motor cortex after hand replantation

In 10 patients, reorganizational changes of the motor cortex contralateral to a replanted hand (MC _replant) were studied one to 14 years after complete traumatic amputation and consecutive successful replantation of the hand. The organizational state of MC _replant was assessed for the deafferentated and peripherally deefferentated hand-associated motor cortex and the adjacent motor representation of the proximal arm. For this, response maps were established for the first dorsal interosseus and biceps brachii muscle using focal transcranial magnetic stimulation (TMS) on a skull surface grid. Characteristics of the maps were center of gravity (COG), number of effective stimulation sites, amplitude sum, and amplitudes and response threshold at the optimal stimulation point. The COG is defined by the spatial distribution of response amplitudes on the map and lies over the cortex region with the most excitable corticospinal neurones supplying the recorded muscle. The COG of the biceps map in MC _replant was shifted laterally by 9.8 ± 3.6 mm (range 5.0-15.7 mm). The extension of the biceps map in MC _replant was increased 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 cortical response map were normal. The different reorganizational phenomena observed for the motor cortical areas supplying the replanted hand and the biceps brachii of the same arm may be influenced by a different extent of deafferentation and by their different role in hand motor control.