Connectivity of the frontal and anterior insular network: a cortico-cortical evoked potential study

OBJECTIVE The frontal and insular fiber network in humans remains largely unknown. This study investigated the connectivity of the frontal and anterior insular network in humans using cortico-cortical evoked potential (CCEP). METHODS This retrospective analysis included 18 patients with medically intractable focal epilepsy who underwent stereoelectroencephalography and CCEP. Alternating 1-Hz electrical stimuli were delivered to parts of the frontal lobe and anterior insula (prefrontal cortex [PFC], ventrolateral and dorsolateral premotor area [vPM and dPM, respectively], presupplementary motor area [pre-SMA], SMA, frontal operculum, and anterior insula). A total of 40-60 stimuli were averaged in each trial to obtain CCEP responses. The distribution of CCEP was evaluated by calculating the root mean square of CCEP responses. RESULTS Stimulation of the PFC elicited prominent CCEP responses in the medial PFC and PMs over the ipsilateral hemisphere. Stimulation of the vPM and dPM induced CCEP responses in the ipsilateral frontoparietal areas. Stimulation of the pre-SMA induced CCEP responses in the ipsilateral medial and lateral frontal areas and contralateral pre-SMA, whereas stimulation of the SMA induced CCEP responses in the bilateral frontoparietal areas. Stimulation of the frontal operculum induced CCEP responses in the ipsilateral insula and temporal operculum. CCEPs were observed in the ipsilateral medial, lateral frontal, and frontotemporal operculum in the anterior insular stimulation. Stimulation of the vPM and SMA led to the network in the dominant hemisphere being more developed. CONCLUSIONS Various regions within the frontal lobe and anterior insula were linked to specific ipsilateral and contra lateral regions, which may reflect distinct functional roles.