Electrical stimulation of the insulo-opercular region: visual phenomena and altered body-ownership symptoms.

PURPOSE: Using direct intracerebral electrical stimulation (ES) in epileptic patients to evoke symptoms to help identify the functional neuroanatomy of the insular lobe and opercula.

METHODS: We selected 43 patients who had at least 1 electrode inserted into the insula or opercula via an oblique approach among 135 patients with intractable epilepsy. Bipolar stimulation was chosen, and the stimulation parameters of the biphasic waves included a pulse width of 0.2 ms, a frequency of 50 Hz, a duration of 3 s, and an intensity gradually increasing from 0.5 to 4 mA.

RESULTS: In total, 93 electrodes were implanted into the insula or insular opercula, and 169 of 281 contacts (60.1%) evoked 212 responses by ES of the insula. 142 responses were induced by stimulating the insular opercula in 126 of 343 sites (36.7%). Usual responses, such as somatosensory, visceral sensory, speech, auditory, and motor responses, were evoked. In addition, rarely reported responses, including cardiovascular symptoms (tachycardia), visual symptoms evoked by ES of the parietal and temporal opercula, and vestibular symptoms (like the loss of ownership of the body) evoked following stimulation of the posterior insula and parietal operculum, were also induced in our study.

CONCLUSIONS: The insula and opercula perform various and complicated functions. The posterior insula and parietal operculum could play important roles in body-ownership symptoms. The complicated visual phenomena were partially related to the temporal operculum.