Plasticity of the somatosensory cortical map in macaque monkeys after chronic partial amputation of a digit

Activity-dependent changes in cortical representational maps have been reported in many studies of adult mammals. Limits in extent of change have been attributed to limited divergence in the thalamocortical projection. However, studies have commonly been restricted to animals surviving less than a year following relatively modest peripheral sensory perturbations. After extensive deafferentation and long-term survival, more extensive changes, seemingly beyond the limits of thalamocortical divergence, have been reported. We report changes in the somatotopic map in area 3b of an adult macaque monkey, in which part of the index finger of one hand had been amputated two years previously. The representation of the remaining stump occupied the whole region of area 3b normally devoted to the representation of the entire digit. The skin surrounding the stump appeared to have been hyperinnervated by axons severed during the amputation. The hyperinnervation of remaining skin may have reactivated neurons of the somatosensory system silenced by the amputation, leading to the recovery of a cortical map but with a modified organization.