The influence of post-nerve injury survival duration on receptive field size: Location, location, location

In the present study, we examined the relationship between post-injury survival duration and receptive field size at multiple levels of the ascending somatosensory neuroaxis. In experimentally naïve subjects, receptive fields on the glabrous hand are typically restricted to single digits. Yet, following targeted nerve section, receptive fields often span multiple digits. In these experiments, adult squirrel monkeys were subject to paired transections of the median and ulnar nerves and permitted to survive for varying periods (2–28 months) prior to terminal electrophysiological recording. The frequency of cutaneously activated multiple-digit receptive fields was evaluated in regions of brainstem, thalamus and cortex normally devoted to the (now) partially deafferented hand. We report that for area 3b of primary somatosensory cortex, receptive field size became smaller as a function of survival duration. In contrast, survival duration had no appreciable effect on the frequency of multiple-digit receptive fields in either the cuneate nucleus of the brainstem or the ventroposterior lateral nucleus of the thalamus. These observations suggest that the mechanisms responsible for the refinement of receptive fields are, primarily, resident to the cortex.