Abstracts

Rationale: A number of investigators have utilized intracranial measurement of cortico-cortical evoked potentials (CCEPs) to delineate the effective connectivity from given sites to distant brain regions. In the present study, we determined the spatiotemporal profiles of CCEP-based connectivity from the stimulation-defined speech arrest sites at the whole brain level. Methods: We studied 16 patients who underwent cortical resection following extra-operative electrocorticography recording and revealed the speech arrest sites in the 50-Hz electrical stimulation mapping. We defined the speech arrest sites as those at which 50-Hz electrical stimulation elicited a transient speech arrest. We measured CCEPs for localization of the remote sites effectively connected to eloquent areas as part of the presurgical epilepsy evaluation. We delivered trains of biphasic single-pulse electrical stimulation to adjacent electrode pairs. At all intracranial electrode sites, we quantified the voltages of CCEPs elicited by single-pulse stimulation of the speech arrest sites. We then animated the dynamics of CCEP voltage changes on the 3D FreeSurfer averaged brain surface image. Results: The 50-Hz electrical stimulation localized the speech arrest sites within the regions proximal to the inferior precentral gyrus on either hemisphere. Single-pulse stimulation of the speech arrest sites elicited an initial negative CCEP component (referred to as N1) at the middle- and inferior-frontal gyri at ≈10 ms, at the post-central and supramarginal gyri at 10-15 ms, superior-temporal gyrus at 15-20 ms, and middle-temporal gyrus at ≈20 ms. Conclusions: Our results suggest that the stimulation-defined speech arrest sites are effectively connected to widespread supra- and infra-sylvian regions on either hemisphere. The observation of N1 latency longer within the infra-sylvian regions compared to within the supra-sylvian regions is consistent with the notion that the N1 component within the infra-sylvian regions reflect neural activation elicited by single-axonal neural propagation via longer white matter fibers. Funding: NIH grant NS064033 (to E. Asano).