Late somatosensory evoked cerebral potentials in response to cutaneous heat stimuli

Late components of cerebral potentials evoked by brief heat pulses applied to various skin sites were used to monitor the afferent pathways of pain and temperature sensitivity. Radiation at 10.6 micron wave length generated by a CO2 laser stimulator predominantly activates superficial cutaneous A delta and C nociceptors and elicits late and ultralate cerebral potentials. This paper deals with the investigation of the component structure and topography of the A delta fibre mediated late potentials, which were compared with the corresponding late potentials in response to standard electrical nerve stimuli. In the upper limb both stimulus types evoked a large positive potential (nerve: 260 msec, skin: 390 msec latency), preceded by a negativity (nerve: 140 msec, skin: 250 msec). Whereas these components were always maximal at the vertex, an earlier negativity appeared over the somatosensory projection area (nerve: 70 msec, skin: 170 msec). After stimulation of the lower limb all latencies were delayed by 20-30 msec. As a rule, the heat-evoked potentials appeared about 100 msec later than the corresponding potentials after electrical nerve stimulation. Similarities in interpeak latencies and scalp topography indicated similar cerebral processing.