LARGE UNRESPONSIVE ZONES APPEAR IN CAT SOMATOSENSORY CORTEX IMMEDIATELY AFTER ULNAR NERVE CUT

The organization of the primary somatosensory cortex innervated by the ulnar nerve was studied before and immediately after ulnar nerve tran section in 11 cats electrophysiologically mapped under Nembutal or Ket amine anesthesia. The cortex was reexamined a second time beginning 42 hr after nerve transection in four cats anesthetized with Nembutal. O ne additional sham-operated control was also mapped. The region of cor tex formerly served by the ulnar nerve remained largely unresponsive t o somatic stimulation independent of the type of anesthetic used durin g recording. Nonetheless, animals anesthetized with Ketamine had more new responsive sites in deafferented cortex following nerve cut than c ats anesthetized with Nembutal. New responses, when observed, were evo ked by stimulation of a region of skin adjacent to the region served b y the ulnar nerve. These findings suggest that the immediate response to deafferentation of somatosensory cortex is a limited acquisition of novel responses restricted to a region immediately adjacent to cortex containing normal afferent input.