Very high frequency oscillations (over 1000 Hz) in human epilepsy.
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.


CONCLUSIONS
Recording of VHFO may be useful for identifying the epileptogenic zone.
Usui
Naotaka
N
National Epilepsy Center, Shizuoka Institute of Epilepsy and Neurological Disorders, Shizuoka, Japan. n-usui@szec.hosp.go.jp
Terada
Kiyohito
K
Baba
Koichi
K
Matsuda
Kazumi
K
Nakamura
Fumihiro
F
Usui
Keiko
K
Tottori
Takayasu
T
Umeoka
Shuichi
S
Fujitani
Shigeru
S
Mihara
Tadahiro
T
Inoue
Yushi
Y
D000293:Adolescent; D000328:Adult; D001683:Biological Clocks / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000379:methods*; D004827:Epilepsy / Q000175:diagnosis* / Q000503:physiopathology*; D006801:Humans; D013355:Subdural Space / Q000502:physiology; D055815:Young Adult