THE CONSISTENCY, EXTENT, AND LOCATIONS OF EARLY-ONSET CHANGES IN CORTICAL NERVE DOMINANCE AGGREGATES FOLLOWING INJURY OF NERVES TO PRIMATE HANDS

The somatosensory cortex of primates contains patch- and bandlike aggr egates of neurons that are dominantly activated by cutaneous inputs fr om the radial, median, and ulnar nerves to the hand. In the present st udy, the area 3b hand cortex of adult monkeys was mapped immediately b efore and after combined median and ulnar nerve transection to evaluat e the consistency, extent, and location of early post-injury alteratio ns in the deprived median and ulnar nerve cortical bands. Several alte rations were observed acutely after injury. (1) The patchlike cortical aggregates of intact radial nerve inputs from the hand underwent a tw o- to three-fold expansion. This expansion was not related to peripher al changes in the radial nerve skin territory, but was due to rapid ce ntral decompression of radial nerve dominance patches. (2) The largest changes involved patches in lateral to central locations of the hand map. (3) The expanded patches occupied cortical zones that were activa ted by inputs from the digits, palm, and posterior hand prior to injur y. These receptive field shifts were initiated within minutes after in jury. (4) Receptive fields of neurons within expanded radial nerve pat ches were normal in size. (5) Besides changes involving radial nerve i nputs from the hand, there was a small expansion of forelimb inputs in to the preinjury hand cortex; however, the representation of face inpu ts did not expand into this cortex. (6) Finally, neurons across 50-69% of the hand cortex were unresponsive to tactile stimuli acutely after this injury. These findings indicate that the distribution patterns o f nerve dominance aggregates in adult primates begin changing within m inutes after nerve injury. Cortical changes involving specific inputs occupy similar extents and locations of cortex, and are arranged in hi ghly consistent patterns, in different individuals. It is suggested th at this consistency reflects specific patterns of central sensitizatio n or disinhibition that are triggered by the injury.