Abstracts

Rationale: The insula harbors areas essential for motor, sensory, auditory and language processing. It is also associated with different pathologies e.g. epilepsy, autism. Most of the evidence about insular connectivity emerged from animals tract tracing and human imaging studies (Cerliani L, Thomas RM, Jbabdi S, Siero JC, Nanetti L, Crippa A, Gazzola V, D'Arceuil H, Keysers C (2011): Probabilistic tractography recovers a rostrocaudal trajectory of connectivity variability in the human insular cortex. Hum Brain Mapp.33: 2005-2034.). Insular functional connectivity can be studied also in patients with refractory epilepsy undergoing intracerebral EEG (icEEG) investigation, by applying electrical stimulation to cortical areas and recording evoked potentials (EP) in distant connected structures.Methods: We used electrical brain stimulation in the context of presurgical evaluation of epileptic patients admitted to our unit. Eleven patients were included. Bipolar electrical stimulation, consisting of two series of 20 pulses of 1 ms duration, 0.2 Hz frequency, and 1 mA intensity, were delivered at each insular contact. For each stimulated insular anatomical region, we calculated a rate of connectivity, reflecting the proportion of other contacts showing significant evoked potentials.Results: Statistically significant evoked potentials were recorded in 74% of intra-insular tested connections and 28% of insular efferents with other cortical regions. Latency averaged 26 3 ms for the intra-insular connections and 33 8 ms for the insular efferents. All insular gyri were interconnected, most connections were reciprocal, showing no clear anterior to posterior directionality. The insula was connected reciprocally with most of the other extra-insular regions. No connection was observed between the right and left insulae. Conclusions: Our findings show for the first time the human functional intra-insular and the insular efferent connections using electrical brain stimulation. These findings point to specific features of Human insula connectivity as compared to non-Human primates, and remain consistent with the complex integration role devoted to the Human insula in many cognitive domains.