Changes in cortical sensory responses with a cryogenic blockade of nucleus ventralis posterolateralis

Abstract

The contribution of nucleus ventralis posterolateralis (VPL) to sensory responses in the cortex of the cat was investigated. Averaged evoked potentials (AEP) were collected in response to paw, click, and light stimuli from primary sensory area S1 and the precruciate (PCA), anterior lateral (ALA), and posterior middle suprasylvian (PMSA) cortical association areas. Activity in VPL was reversibly blocked using a cryoprobe system to produce localized cooling. Reduction in amplitude of the short latency component of the AEP in S1 in response to the paw stimulus indicated that VPL was blocked. The short latency component of responses in the three association cortices was also blocked by cooling VPL, but the latency of this component was 20 msec longer than that of S1. Cross-correlation analyses of AEPs were performed to evaluate waveform similarity. Responses in a single cortical area to two different stimulus modalities or responses in two different cortical areas to one stimulus modality had about the same degree of waveform similarity. The effect of cooling VPL on waveform similarity was minimal and was not consistent for either stimulus pairs or cortical pairs. We concluded that VPL contributes to short latency responses in association cortices, but by a projection system differing from that to S1 since the latency to the changed response component was 20 msec longer than that observed for S1 cortex. Some similarity of sensory response waveform was found, but VPL makes little or no contribution to this similarity. No evidence was found for covariation of response excitability in cortical areas.