title: High frequency oscillations in early cortical somatosensory evoked potentials.
abstract: 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.
authors.affiliation: Third Department of Medicine, Hirosaki University School of Medicine, Japan. isamu@cc.hirosaki-u.ac.jp
authors.forename: I
authors.initials: I
authors.lastname: Ozaki
authors.forename: C
authors.initials: C
authors.lastname: Suzuki
authors.forename: Y
authors.initials: Y
authors.lastname: Yaegashi
authors.forename: M
authors.initials: M
authors.lastname: Baba
authors.forename: M
authors.initials: M
authors.lastname: Matsunaga
authors.forename: I
authors.initials: I
authors.lastname: Hashimoto
mesh_terms: 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