Intracranial electrical stimulations of human insular cortex: A stereo-EEG study in patients with drug-resistant focal epilepsy

The insular lobe is the less known of human cerebral lobes and few researches have been performed in order to comprehend its function. Lesional and functional neuroimaging studies were initially performed suggesting different roles of the insular lobe. More recently intracranial stimulation studies had contributed to understand the functions of the human insula. We studied the clinical manifestations induced by intracerebral electrical stimulations performed during the pre-surgical work-out in 96 epileptic patients submitted to SEEG, with at least one electrode exploring the insular cortex. In order to precisely localize the position of the electrodes we carried out a postoperative 3D CT-scan or a 3D MRI, and then we fused the images with the preoperative MRI in the same stereotactic referenced system. Electrical bipolar stimulations were carried out at low frequency and high frequency. The most frequent induced symptom was a somatosensory manifestation (72%), mainly paresthesic sensation involving the contralateral face and upper limb, while other types of clinical modification were extremely infrequent. Our data provide evidence of a prominent somatosensory role of the human insular cortex. The fusion imaging methodology enabled us to precisely localize the stimulated contacts, excluding those that were not located into the insular cortex, probably explaining the higher amount of sensory manifestations respect to previous articles.