High frequency oscillations in early cortical somatosensory evoked potentials.
OBJECTIVE
To evaluate the characteristics of high frequency (HF) components of the early cortical somatosensory evoked potentials (SEPs).


METHODS
We recorded 8-channel SEPs from the frontal and left centro-parietal scalp after right median nerve stimulation with a wide band-pass (0.5-2000 Hz) and digitized at 40 kHz sampling rate in 12 healthy subjects. HF components were analyzed after digital band-pass filtering (300-1000 Hz). The power spectrum was obtained by a maximum entropy method.


RESULTS
HF oscillations (maximum power at 600-800 Hz) consisting of 5 to 8 peaks were discriminated from the preceding P14 far-field in all cases and their phases were reversed between the frontal and contralateral parietal regions. In addition, in subjects with a high amplitude central P22 potential in original wide-band recordings, a single HF oscillation with a maximum at the central region was present. Furthermore, this component showed no phase reversal over the centro-parietal area.


CONCLUSIONS
We therefore conclude that HF oscillations are superimposed not only on the tangential N20-P20 but on the radial P22 potential, and are generated from both tangential (area 3b) and radial (area 1) current sources.
Ozaki
I
I
Third Department of Medicine, Hirosaki University School of Medicine, Japan. isamu@cc.hirosaki-u.ac.jp
Suzuki
C
C
Yaegashi
Y
Y
Baba
M
M
Matsunaga
M
M
Hashimoto
I
I
D000328:Adult; D002540:Cerebral Cortex / Q000502:physiology*; D004558:Electric Stimulation; D019277:Entropy; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology; D009991:Oscillometry