S43 Insular semiology: From observation of cases to cortical stimulation

Abstract

Objectives Stereotactic stimulations of the insular cortex through intracranial electrodes aim at characterizing the semiology of insular seizures. These stimulations, carried out in the context of Stereo-Electro-Encephalography (SEEG) during pre-surgical monitoring of epilepsy, reproduce the ictal symptoms observed during the development of insular seizures. Methods We reviewed the results of insular stimulations performed in 222 patients admitted between 1997 and 2015 for pre-surgical SEEG exploration of atypical temporal or perisylvian epilepsy. Stimulations (50 Hz, trains of 5s, pulses of 0.5 ms, intensity 0.2–3.5 mA) were carried out using trans-opercular electrodes implanted orthogonal to mid-sagittal plane. Results 550 of 669 stimulations were clinically eloquent in the absence of any post-discharge (237 and 313 respectively in right and left insula). Somatosensory responses (61% of evoked sensations) including pain and visceral sensations (14.9%) were the most frequent, followed by auditory sensations (8%), vestibular illusions (7.5%), speech impairment (5%), gustatory, (2.7%) and olfactory (1%) sensations. Although these responses showed some functional segregation (in particular a privileged pain representation in the postero-superior quadrant), there was a clear spatial overlap between representations of the different modalities. Discussion Symptoms evoked by insular stimulations are multiple. None of them can be considered as absolutely specific to the insular cortex, but the occurrence in given seizure of a somatosensory symptom such as pain or of a laryngeal spasm associated to vestibular, auditory, aphasic, or olfacto-gustatory symptoms points to a discharge development in the insular cortex. Conclusion Inular cortex is the only cortical region where stimulations demonstrate such a multi-modal representation.