NMDA RECEPTORS AND PLASTICITY IN ADULT PRIMATE SOMATOSENSORY CORTEX

Topographic maps in adult primate somatosensory cortex are capable of dramatic reorganizations after peripheral nerve injuries. In the prese nt experiments, we have deprived a circumscribed portion of the hand m ap in somatosensory cortex of four adult squirrel monkeys by transecti ng the median nerve to one hand, and evaluated the hypothesis that N-m ethyl-d-aspartate (NMDA) glutamatergic receptors are necessary for the reorganization that follows within four weeks. In one monkey, we conf irm previous results demonstrating that the deprived cortex has regain ed responsiveness in its expanse four weeks after median nerve transec tion. However, in three monkeys in which NMDA receptors were concurren tly blocked, most of the deprived cortex remained unresponsive. Thus, much of the cortical ''recovery'' that typically follows peripheral ne rve injury in adult monkeys is apparently dependent on NMDA receptors and may well be due to Hebbian-like changes in synaptic strength. Perh aps the elimination of the normally dominant inputs to ''median nerve cortex'' permits the gradual strengthening of correlations between the activity of the formally impotent presynaptic and deprived postsynapt ic elements. These enhanced correlations may also have been made possi ble by reductions in intracortical inhibition as a necessary but not s ufficient condition. (C) 1996 Wiley-Liss, Inc.