A white matter tract mediating awareness of speech.

OBJECTIVE To investigate the effects of extraoperative electrical stimulation of fiber tracts connecting the language territories. METHODS We describe results of extraoperative electrical stimulation of stereotactic electrodes in 3 patients with epilepsy who underwent presurgical evaluation for epilepsy surgery. Contacts of these electrodes sampled, among other structures, the suprainsular white matter of the left hemisphere. RESULTS Aside from speech disturbance and speech arrest, subcortical electrical stimulation of white matter tracts directly superior to the insula representing the anterior part of the arcuate fascicle, reproducibly induced complex verbal auditory phenomena including (1) hearing one's own voice in the absence of overt speech, and (2) lack of perception of arrest or alteration in ongoing repetition of words. CONCLUSION These results represent direct evidence that the anterior part of the arcuate fascicle is part of a network that is important in the mediation of speech planning and awareness likely by linking the language areas of the inferior parietal and posterior inferior frontal cortices. More specifically, our observations suggest that this structure may be relevant to the pathophysiology of thought disorders and auditory verbal hallucinations.