Abstracts

Rationale: Humans communicate with others using a series of facial movements, and selective damage to the primary face motor area frequently leads to dysarthria. We hypothesized that the primary face motor area would consist of an integral part of the auditory language network and thus have effective connectivity to the language areas in the left frontal and temporal lobes. To address this hypothesis, we measured cortico-cortical evoked potentials (CCEPs) on subdural EEG recording and determined the spatial extent of effective connectivity from the primary face motor area within each hemisphere. Methods: This study has been approved by our Institutional Review Board, and informed consent was obtained from the patients or the guardian of pediatric patients. We studied 19 patients with intractable focal epilepsy who underwent functional brain mapping using 50-Hz electrical stimulation and measurement of CCEPs during invasive monitoring. We delivered trains of single-pulse stimulation to the primary face motor area and outlined the spatial extent of resulting CCEPs at the whole brain level. We finally animated the dynamics of CCEP voltage changes on the 3D brain surface image. Results: The 50-Hz electrical stimulation localized the primary face motor area within the pre- and post-central gyri in either hemisphere. Single-pulse stimulation of the primary face motor area elicited early negative CCEPs (referred to as N1) at the posterior inferior-frontal, supra-marginal, and posterior superior-temporal gyri within 20 ms in each hemisphere. N1 involved the middle-temporal gyrus of either hemisphere only modestly within 40 ms. The spatial extent of late negative CCEPs (N2) was similar to that of N1. The study failed to show discernible left-hemispheric dominance of N1 or N2 responses. Conclusions: We provided evidence that the primary face motor area is effectively connected to the left posterior inferior-frontal and posterior superior-temporal gyri often considered to be a part of language areas to be preserved in epilepsy surgery. Nonetheless, the effective connectivity from the primary face motor area may not be specific to the pathways subserving semantic-syntactic processing, taking into account the lack of left-hemispheric dominant N1/N2 responses in the present study. Funding: NIH grant NS064033 (to E. Asano)