Very high frequency oscillations (over 1000 Hz) in human epilepsy
Naotaka Usui1, Kiyohito Terada, Koichi Baba
1National Epilepsy Center, Shizuoka Institute of Epilepsy and Neurological Disorders, Shizuoka, Japan. n-usui@szec.hosp.go.jp
Objective:
High frequency oscillations (HFO) of 100-500Hz have been reported in epileptic human brain. However, the questions of how fast these oscillations can reach, and which frequency range is clinically important remain unanswered. We recorded interictal and ictal very high frequency oscillations (VHFO) of 1000-2500Hz by subdural electrodes using 10kHz sampling rate. We describe the characteristics of VHFO, and discuss their underlying mechanism and clinical significance.
Methods:
Five patients with neocortical epilepsy were studied. All patients underwent intracranial EEG monitoring with subdural electrodes. EEG recording with sampling rate of 10kHz was conducted. Histopathology revealed malformation of cortical development in all cases.
Results:
In four of five patients, very high frequency activities of 1000-2500Hz were detected in highly localized cortical regions (one to four electrodes in individual patient). We named these activities "very high frequency oscillations (VHFO)". Interictally, VHFO appeared intermittently, and were interrupted by spikes. Sustained VHFO without spikes appeared around the start of seizures.
Conclusions:
Both interictal and ictal VHFO can be recorded by subdural electrodes. Compared to HFO previously reported, VHFO have much higher frequency, more restricted distribution, smaller amplitude, and different timing of onset.
Significance:
Recording of VHFO may be useful for identifying the epileptogenic zone.
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