Functional Mapping of the Insular Cortex: Clinical Implication in Temporal Lobe Epilepsy

Abstract

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...

Localization of Abnormal Discharges Causing Insular Epilepsy by Magnetoencephalography

“…This spike type, also known to be common in TLE , may represent temporal lobe activity propagated from the insula. The insular cortex is known to have dense neuronal connections to the temporal cortex (Penfield and Faulk 1955;Augustine 1996;Isnard et al 2000;Ostrowsky et al 2000). Consequently, insular epilepsy and TLE are likely to have common clinical features as well as similar scalp EEG distribution and MEG localization of E/ M-spikes.…”

“…Scalp electroencephalography (EEG) is relatively insensitive to detect neuronal activity in the insula because of this deep location, so insular epilepsy is rarely reported (Fiol et al 1988;Cukiert et al 1998). Furthermore, the insular cortex has multiple connections with the adjacent cerebral cortex, especially with the temporal lobe (Penfield and Faulk 1955;Augustine 1996), so that insular epilepsy shares similar clinical features with temporal lobe epilepsy (TLE), including nausea, abnormal throat sensation, epigastric discomfort, chewing, and lip smacking (Fiol et al 1988;Roper et al 1993;Cukiert et al 1998;Ostrowsky et al 2000). Scalp EEG localizes the epileptic discharges of both TLE and insular epilepsy in the anterior temporal lobe.…”

Presurgical Assessment of Patients with Refractory Temporal Lobe Epilepsy

“…Extreme bradycardia and even atrioventricular block has been described when compromising autonomic control centers at the temporal lobe. As a general rule, the autonomic manifestations of temporal lobe seizures such as ictal vomiting, urinary urgency, spitting, tend to lateralize to the non-dominant hemisphere for language (Ostrowsky, 2000). Ictal vomiting may be the only manifestation of simple partial seizures, and has been linked to temporal lobe seizures in the non-dominant hemisphere (Kotagal, 1995;Devinsky, 1995).…”

Insular epilepsy surgery under neuronavigation guidance using depth electrode

“…The insular cortex hidden by the frontal or temporal operculum can be an epileptic zone [3,14,15]. Seizures originating in the insular cortex used to be confused with frontal, temporal, or frontotemporal lobe seizures.…”

“…Because of its location deep within the sylvian fissure, scalp electroencephalography is relatively insensitive [3,24]. The implantation of subdural electrodes, such as transsylvian or stereotactic depth electrodes, perpendicular to the midsagittal plane by the transopercular route can be used for limited monitoring of the wide insular cortex [3,14].…”