• Katsuya Kobayashi, Riki Matsumoto, Masao Matsuhashi, Kiyohide Usami, Akihiro Shimotake, Takeharu Kunieda, Takayuki Kikuchi, Kazumichi Yoshida, Nobuhiro Mikuni, Susumu Miyamoto, Hidenao Fukuyama, Ryosuke Takahashi, and Akio Ikeda.
• Department of Neurology, Kyoto University Graduate School of Medicine, 54, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan. Electronic address: 31258a@kuhp.kyoto-u.ac.jp.
• Clin Neurophysiol. 2017 Sep 1; 128 (9): 1673-1681.

ObjectiveWe aimed to clarify that high frequency activity (HFA) of cortico-cortical evoked potentials (CCEPs), elicited by single pulse electrical stimulation (SPES), reflects cortical excitability.MethodsWe recruited 16 patients with refractory partial epilepsy who had chronic subdural electrode implantation for presurgical evaluation. A repetitive SPES was given to (1) the seizure onset zone (SOZ) and (2) the control cortices (non-seizure onset zone: nSOZ). CCEPs were recorded from the neighboring cortices within SOZ and nSOZ. We applied short-time Fourier transform to obtain the induced responses for the timing of early (<50ms after SPES) and late CCEP components and analyzed the logarithmic power change for ripple (<200Hz) and fast ripple (>200Hz) bands.ResultsTwenty-one clear CCEPs were recorded for both the SOZ and nSOZ. The HFA power of early CCEPs in SOZ significantly increased compared to that in nSOZ in both frequency bands, particularly in mesial temporal lobe epilepsy (MTLE).ConclusionSimilar to the features of spontaneous pathological HFOs, the power of stimulus-induced HFAs in SOZ were greater than that outside SOZ, particularly in MTLE.SignificanceHFA overriding CCEPs can be a surrogate marker of cortical excitability in epileptic focus.Copyright © 2017 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.

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