Abstracts

Rationale: Virtual lesioning with 50-Hz electrical stimulation is widely employed to localize functionally-important areas, whereas measurement of remote cortical responses to 1-Hz single-pulse stimulation is useful to characterize the effective connectivity from a given stimulus site. In this study, we identified the expressive aphasia sites in the left frontal lobe using 50-Hz electrical stimulation. We subsequently determined the spatial extent of effective connectivity from the left frontal expressive aphasia sites by measuring cortico-cortical evoked potentials (CCEPs) elicited by 1-Hz single-pulse stimulation.  Methods: Our study included five right-handed patients who were evaluated with extraoperative electrocorticography, 50-Hz stimulation mapping, and measurement of CCEPs. We quantified the voltages of CCEPs elicited by single-pulse stimulation of the left frontal expressive aphasia sites. We subsequently animated the rapid change of CCEP voltages on the three-dimensional MR image with a temporal resolution of 1 ms.  Results: The expressive aphasia sites involved the left inferior-, middle-, and superior-frontal gyri. Single-pulse stimulation of the expressive aphasia sites elicited a negative CCEP component (N1) at the surrounding regions in an anterior-to-posterior direction. Specifically, N1 involved the posterior frontal areas including the precentral gyrus within 20 ms, the posterior superior-temporal and middle-temporal gyri within 25 ms, and the supramarginal gyrus within 30 ms.  Conclusions: The left frontal expressive aphasia sites were distributed to broad areas within the left frontal lobe, and effectively connected to the posterior language areas including the superior-temporal, middle-temporal, and supramarginal gyri. Funding: No funding