Cortical potentials evoked by innocuous tactile and noxious thermal stimulation in the rat: differences in localization and latency

Abstract

Thermal stimulation of the rat hindleg at noxious intensities produced by laser-emitted radiant heat yielded replicable average evoked responses (AERs) in contralateral primary somatosensory cortex. In monopolar recordings, responses of opposite polarity were observed at the same depth at sites surrounding the point yielding maximum amplitude responses; potentials recorded at both central and surround sites reversed polarity in depth recordings. Compared to responses evoked by innocuous tactile stimulation, AERs to noxious thermal stimuli exhibited longer peak latencies, a more posterior localization, and a relatively higher amplitude negative component; all of these differences were statistically significant. These findings may reflect differences in central sensory mechanisms mediating the two types of stimuli and indicate the utility of the present technique for studying central mechanisms of pain perception.