Functional connectivity of insular efferences

Objectives: The aim of our study was to explore the functional connectivity between the insula and other cortical regions, in human, using cortico-cortical evoked potentials (CCEPs) Experimental design: We performed intra-cerebral electrical stimulation in eleven patients with refractory epilepsy investigated with depth electrodes, including 39 targeting the insula. Electrical stimulation consisted of two series of 20 pulses of 1-ms duration, 0.2-Hz frequency, and 1-mA intensity delivered at each of the 39 insular bipoles. Rates of connectivity were reported whenever a noninsular cortical region was tested by at least ten stimulating/recording electrode pairs in three or more patients Results: Significant CCEPs were elicited in 193 of the 578 (33%) tested connections, with an average latency of 33±5 ms. The highest connectivity rates were observed with the nearby perisylvian structures (59%), followed by the pericentral cortex (38%), the temporal neocortex (28%), the lateral parietal cortex (26%), the orbitofrontal cortex (25%), the mesial temporal structures (24%), the dorsolateral frontal cortex (15%), the temporal pole (14%), and the mesial parietal cortex (11%). No connectivity was detected in the mesial frontal cortex or cingulate gyrus. The pattern of connectivity also differed between the five insular gyri, with greater connectivity rate for the posterior short gyrus (49%), than for the middle short (29%), and two long gyri (28 and 33%) Conclusion: The human insula is characterized by a rich and complex connectivity that varies as a function of the insular gyrus and appears to partly differ from the efferences described in nonhuman primates.