Detection of seizure-associated high-frequency oscillations above 500Hz

Kobayashi, Katsuhiro; Agari, Takashi; Oka, Makio; Yoshinaga, Harumi; Date, Isao; Ohtsuka, Yoko; Gotman, Jean

doi:10.1016/j.eplepsyres.2009.10.008

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Volume 88, Issue 2 , Pages 139-144, February 2010

Detection of seizure-associated high-frequency oscillations above 500Hz

Katsuhiro Kobayashi
- Department of Child Neurology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, and Okayama University Hospital, Shikatacho 2-chome 5-1, Kita-ku, Okayama 700-8558, Japan
- Corresponding author. Tel.: +81 86 235 7372; fax: +81 86 235 7377.
Takashi Agari
- Department of Neurological Surgery, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, and Okayama University Hospital, Shikatacho 2-chome 5-1, Kita-ku, Okayama 700-8558, Japan
Makio Oka
- Department of Child Neurology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, and Okayama University Hospital, Shikatacho 2-chome 5-1, Kita-ku, Okayama 700-8558, Japan
Harumi Yoshinaga
- Department of Child Neurology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, and Okayama University Hospital, Shikatacho 2-chome 5-1, Kita-ku, Okayama 700-8558, Japan
Isao Date
- Department of Neurological Surgery, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, and Okayama University Hospital, Shikatacho 2-chome 5-1, Kita-ku, Okayama 700-8558, Japan
Yoko Ohtsuka
- Department of Child Neurology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, and Okayama University Hospital, Shikatacho 2-chome 5-1, Kita-ku, Okayama 700-8558, Japan
Jean Gotman
- Montreal Neurological Institute, McGill University, 3801 University Street, Montreal, Quebec, Canada H3A 2B4

Received 27 August 2009; received in revised form 6 October 2009; accepted 15 October 2009.

Summary

High-frequency oscillations (HFOs) of up to 500Hz in EEG are considered to have close relation with ictogenesis. We had the unique opportunity to record a seizure in EEG with intracerebral macroelectrodes and a sampling frequency of 10kHz. Considering the notion that faster HFOs are likely more ictogenic, we investigated this ictal EEG data to find if even faster HFOs were present.

HFOs were investigated in interictal spikes and seizure activity using time–frequency spectra: t values corresponding to frequencies from 100 to 1000Hz were obtained by comparison to the background and controlled by the false discovery rate (FDR).

The seizure had a right hippocampal onset. HFOs up to 800Hz as well as HFOs below 500Hz built up in the hippocampal discharges more at the beginning of the seizure and during the preictal period than in the interictal period. These HFOs were visually confirmed in temporally expanded EEG traces.

We demonstrated for the first time the existence of HFOs above 500Hz and up to 800Hz with intracerebral macroelectrodes in an epileptic patient; they occurred primarily in association with the seizure discharge. HFOs above 500Hz possibly reflect facilitation of ictogenic neuronal hypersynchronization.

Keywords: High-frequency oscillation, Mesial temporal lobe epilepsy, Ictal EEG, Time–frequency analysis, False discovery rate