We studied painful and non-painful somaesthetic sensations elicited by direct electrical stimulations of the insular cortex performed in 43 patients with drug refractory temporal lobe epilepsy, using stereotactically implanted depth electrodes. Painful sensations were evoked in the upper posterior part of the insular cortex in 14 patients, mostly in the right hemisphere. Non-painful sensations were elicited in the posterior part of the insular cortex in 16 patients, in both hemispheres. Thus, painful and non-painful somaesthetic representations in the human insula overlap. Both types of responses showed a trend toward a somatotopic organization. These results agree with previous anatomical and unit recording studies in monkeys indicating a participation of the posterior part of the insular cortex in processing both noxious and innocuous somaesthetic stimuli. In humans, both a posterior and an anterior pain-related cortical area have been described within the insular cortex using functional imaging. Our results help to define the respective functional roles of these two insular areas. Finally, lateralization in the right hemisphere of sites where painful sensations were evoked is coherent with the hypothesis of a preponderant role of this hemisphere in species survival.

The role of the insular cortex in the genesis of temporal lobe epileptic (TLE) seizures has been investigated in 21 patients with drug‐refractory TLE using chronic depth stereotactic recordings of the insular cortex activity and video recordings of ictal symptoms during 81 spontaneous electroclinical seizures. All of the recorded seizures were found to invade the insula, most often after a relay in the ipsilateral hippocampus (19/21 patients). However, 2 patients had seizures that originated in the insular cortex itself. Ictal symptoms associated with the insular discharges were similar to those usually attributed to mesial temporal lobe seizures, so that scalp video‐electroencephalographic monitoring does not permit making any difference between ictal symptoms of temporo‐mesial and insular discharges. A favorable outcome was obtained after a temporal cortectomy sparing the insular cortex in 15 of 17 operated patients. Seizures propagating to the insular cortex were found to be fully controlled by surgery, whereas those originating in the insular cortex persisted after temporal cortectomy. The fact that seizures originating in the insular cortex are not influenced by temporal lobectomy is likely to explain some of the failures of this surgical procedure in TLE. Ann Neurol 2000;48:614–623

Summary: Purpose:We report the results of 75 intracortical electrical stimulations of the insular cortex performed in 14 patients during stereo-electroencephalography (SEEG) investigation of drug-resistant partial epilepsy. The insular cortex was investigated on electroclinical arguments suggesting the possibility of a perisylvian spread or a rapid multilobar diffusion of the discharges during video EEG.Methods: In these 14 patients, 27 stereotactically implanted transopercular electrodes reached the insular cortex (1 1 the right insula, 16 the left insula). Square pulses of current were applied between the two deepest adjacent contacts of each transopercular electrode using low (1 Hz) or high-frequency (50 Hz) stimulation. Only symptoms evoked in the absence of afterdischarges were analyzed.Results: Clinical responses were evoked in 10 of the 14 patients (in 20 of the 27 insular sites) and showed a clear topographic specificity inside the insular cortex. Viscerosensitive and visceromotor responses, similar to those evoked by temporomesial stimulation, were evoked by anterior insular stimulation and somesthetic sensation, similar to those evoked by opercular cortex stimulation, by posterior insular stimulation.Conclusions: The topographic organization of the induced responses within the insular cortex suggest that two different cortical networks, a visceral network extending to the temporomesial structures and a somesthetic network reaching the opercular cortex, are disturbed with stimulation of the anterior or the posterior insula, respectively. Thus ictal symptoms associated with the spread of the epileptic discharges to the insular cortex might be difficult to distinguish from those usually reported during temporomesial or opercular discharges. Key Words: Insula of Reil-Temporal lobe-Epilepsy-Stereoelectroencephalography-Stimulation.Lesional and functional data available in humans suggest that the paralimbic insular cortex is involved in visceromotor, viscerosensitive, and somesthetic functions as well as in motor, pain, and speech functions (1). The insular cortex has rarely been investigated using depth electrodes because of its anatomic location, burried under the frontal, temporal, and parietal opercular cortices and separated from them by a dense wall of arteries running in the sylvian fissure. Three previous studies are available in the literature concerning direct stimulation of the human insular cortex. Penfield and Faulk, 1955 (2), reported evoked visceromotor, viscerosensitive, gustatory, and somesthetic responses after stimulation of the inferior part of the insular cortex during intrasurgical procedures. Using stereo-electroencephalography (SEEG), Wieser, 1983 (3), concluded that 5140% of Accepted January 19, 2000. Address correspondence and reprint requests to Dr. K. Ostrowsky at Functional Neurology and Epileptology Department, H8pital Neurologique, 59 Boulevard Pinel, 69300 Lyon, France. insular cortex stimulations evoke visceral sensations. Oppenheimer et al. 1992 (4), focused on cardiac rhy...

This is the first quantitative SEEG study providing insight into the mechanisms generating seizures in nodular heterotopia. We demonstrate that both the heterotopic lesion and particularly the normotopic cortex are involved in the epileptogenic network. This could open new perspectives on multitarget treatments, other than resective surgery, aimed at modifying the epileptic network.