INPUT-INCREASE AND INPUT-DECREASE TYPES OF CORTICAL REORGANIZATION AFTER UPPER EXTREMITY AMPUTATION IN HUMANS

A plastic remodeling of regions in somatosensory cortex has previously been observed to occur in separate experimental paradigms in response to loss of somatosensory input and to increase in input. In this stud y, both types of cortical reorganization have been observed to occur c oncurrently in the same adult human nervous system as a result of a si ngle intervention, Following upper extremity amputation, magnetic sour ce imaging revealed that tactile stimulation of the lip evoked respons es not only in the area of the somatosensory cortex corresponding to t he face, but also within the cortical region that would normally corre spond to the now absent hand. This ''invasion'' of the cortical amputa tion zone was accompanied by a significant increase in the size of the representation of the digits of the intact hand, presumably as a resu lt of an increased importance of sensory stimulation consequent to inc reased dependence on that hand imposed by the loss of the contralatera l extremity.