Somatotopic consolidation: a third phase of reorganization after peripheral nerve injury in adult squirrel monkeys.

It has previously been demonstrated that the central somatosensory topographic reorganization within deprived cortex that follows peripheral nerve injury in adult monkeys occurs in at least two stages: an immediate unmasking period; and a more prolonged period where deprived areas of cortex come to express new receptive fields in a topographically arranged manner. In the present experiments, we have compared cortical topography many months after combined median and ulnar nerve transection with "complete" reorganization evident at relatively short (i.e., 2-5 months) survival times. We find further reorganizational changes in cortical topography with longer survival times. That is, the roughly somatotopic, generally multiple-digit receptive fields frequently observed at the shorter survival times are generally sharpened to more distinct, single-digit receptive fields at longer survival times. We hypothesize that the early crudely topographic maps reflect all available inputs while the refined map is the outcome of an extraction process where only the most useful subset of available inputs is expressed. It is further suggested that this distillation process is a use-dependent phenomenon.