Dipole Source Analysis of Laser-Evoked Subdural Potentials Recorded From Parasylvian Cortex in Humans

The location of the human nociceptive area(s) near the Sylvian fissure is still controversial in spite of evidence from imaging and evoked potential studies that noxious heat stimuli activate somatosensory areas in that region. Some studies have suggested the secondary somatosensory cortex (SII) on the upper bank of the Sylvian fissure posterior to the central sulcus, others the anterior insula or parietal area 7b. In this study, we applied dipole source analysis techniques to laser-evoked potentials (LEPs) that were recorded from subdural grid electrodes in three patients. As a functional marker, auditory-evoked potentials (AEPs) with a generator on the opposite bank of the Sylvian fissure were recorded from the same electrodes. The LEP global field power (GFP), a measure of spatial variance, showed a first peak at about 150 ms latency, corresponding to the latency of the N1 recorded from the scalp. In contrast to scalp recordings, the amplitude of the first GFP peak recorded from the grid was larger tha...