The role of parietal opercular and insular cortex in somatosensory
François Mauguière
and pain sensation in humansFunctional Neurology and Epileptology Department, Neurological Hospital, 69003 Lyon, France
All models of median nerve (MN) somatosensory and CO2-laser evoked SEPs or SEFs include sources located in the upper bank of the Sylvian fissure, contra- and ipsilateral to stimulation. Intracerebral recordings using depth electrodes implanted perpendicular to the cortical surface, as performed during presurgical Stereo-EEG investigations of patients with partial epileptic seizures, offer the possibility to assess the waveform, latencies, and sources of somatosensory and pain evoked potentials. Intracerebral recordings show that the SII area and the insular cortex are involved in the processing of normal somatosensory and pain sensation. Intracortical EPs to CO2-laser stimulation recorded in the upper bank of the Sylvian fissure and in the insular cortex peak in the 140 - 200 ms latency range (N140 - P170) and are maximal at a depth of 40 - 50 mm from midline. This location is similar to that of responses to electric median nerve stimulation which in the 60 - 90 ms latency range (N60 - P90). These data converge to the conclusion that the parietal-opercular and insular cortex might play a role in the integration of noxious and non-noxious inputs as suggested by previous modelling studies of SEFs. Moreover, the recording of polarity reversal along the axis of electrode tracks perpendicular to the scalp surface, using a remote earlobe reference electrode, suggests that some of the dipolar sources of somatosensory and pain responses in SII are radial to the scalp surface.
