EVOLUTION OF CORTICAL RESPONSIVENESS SUBSEQUENT TO MULTIPLE FORELIMB NERVE TRANSECTIONS - AN ELECTROPHYSIOLOGICAL STUDY IN ADULT CAT SOMATOSENSORY CORTEX

Multiunit recordings along mediolateral rows in the primary somatosens ory cortex of the animals described by C. Avendano, D. Umbriaco, R.W. Dykes, and L. Descarries (1995, J. Comp. Neurol. 354:321-332) provided information about the functional status of the regions in and near th e deafferented cortex. Responses changed along this axis from normally organized receptive fields in the hindlimb representation through a t ransition zone of unusually small receptive fields into the clearly de afferented forelimb representation, where receptive fields were uncomm on and often had unusual characteristics. The most abrupt change along this axis was the appearance of a repetitive, bursting discharge patt ern in the multiunit activity near the border of the deprived cortex. The appearance of this pattern was used as a reference to describe dif ferences between normal and deprived cortices. The nature of these dif ferences evolved with time. Much of the deprived cortex lacked identif iable receptive fields for months after the nerve transections and, 1 year later, still only about half of the recording sites within the de prived region displayed organized receptive fields. Some sites within the deprived region lacking definable receptive fields could be excite d at long latencies by somatic stimuli anywhere on the body. With time , regions of normal cortex near the border with the deprived zone beca me more involved in these processes. Spontaneous activity and threshol ds also changed with time in both normal and deprived cortices. These electrophysiological responses occurred during a time when choline ace tyltransferase staining was reduced in and around the deprived cortex (Avendano et al., 1995); the effects of nerve transections were most p ronounced between the 8th and 13th weeks, as was the reduction in immu nostaining; however, although immunostaining had returned to normal le vels at 1 year, many parts of the deprived cortex remained without new afferent drive, some being unresponsive to any somatic stimuli. (C) 1 995 Wiley-Liss, Inc.