Few data exist about of the role of the insula in the processing of speech. The data of this study suggests the involvement of the upper middle short gyrus in speech production.

For this study, we included 25 patients suffering from severe drug refractory partial epilepsy were investigated by stereo-electroencephalography (SEEG). At least one electrode was used to explore the insular cortex using an oblique approach (trans-frontal or trans-parietal) and who had a normal insular region. In total, 313 stimulations were performed in 27 insula. Eighty-three responses induced by insular electrical stimulation (ES), eight (9.6%) were reported by five patients as speech arrest (5 responses) and a lowering of voice intensity (3 responses). The stereotactic approach allows us to identify the stimulation sites within the insular cortex in terms of its gyri and sulci. Also, the stimulation sites were anatomically localized via image fusion between pre-implantation 3D MRI and post-implantation 3D CT scans revealing the electrode contacts.

Eight responses were reported as speech disturbances. 7 among them were evoked in 4 patients by stimulation in the middle short gyrus (8.4% of total responses, and 25.9% of responses evoked in the middle short gyrus). The site of the 8th response was in the post-central insular gyrus in the same insular region where the oropharyngeal responses induced by other ES (pharyngeal construction) in this study. The data suggest the involvement of the middle short gyrus of the insula in the procedures of language. These responses were evoked in the non-dominant side four times out of five. This study provides evidence that the middle short gyrus of the insula in both hemispheres responds to ES producing speech disturbances.

The results of this study are the first to report language disorders in humans evoked by electrical stimulation of the insular cortex during SEEG explorations by electrodes implanted by oblique approach in terms of gyral and sulcal anatomy.