title: Diurnal variations in alpha power density and subjective sleepiness while performing repeated vigilance tasks.
abstract: OBJECTIVE
  Diurnal variations in EEG activity and subjectively rated sleepiness while performing repeated vigilance tasks were examined.
  
  
  METHODS
  Nine diurnally active healthy males underwent repeated vigilance tasks at 08:00, 11:00, 14:00, 17:00 and 20:00 h. An electroencephalogram (EEG) was taken while the subjects performed the tasks with their eyes open. The alpha power spectra (8.6-13.3 Hz) of EEG was integrated. Subjectively rated sleepiness, reaction time and oral temperature were also measured.
  
  
  RESULTS
  Significant diurnal variations were found for alpha power, subjectively rated sleepiness and oral temperature. The alpha power was significantly smaller at 08:00 than at 11:00, 14:00, 17:00 and 20:00 h. The subjectively rated sleepiness was significantly larger at 08:00 than at 11:00, 17:00 and 20:00 h. The diurnal variation in alpha power did not correspond to that in subjectively rated sleepiness. On the other hand, repeated vigilance tasks increased the alpha power, subjectively rated sleepiness and reaction time at each time of day. The increase in alpha power was significantly greater at 14:00 than at 08:00 and 20:00 h.
  
  
  CONCLUSIONS
  The diurnal variation was found in alpha power while performing vigilance tasks. Furthermore, the increase in alpha power with repetition of the task depended on the time of day.
authors.affiliation: Department of Public Health, Akita University School of Medicine, 1-1-1 Hondo, 010-8543, Akita City, Japan. higuchi@med.akita-u.ac.jp
authors.forename: S
authors.initials: S
authors.lastname: Higuchi
authors.forename: Y
authors.initials: Y
authors.lastname: Liu
authors.forename: T
authors.initials: T
authors.lastname: Yuasa
authors.forename: A
authors.initials: A
authors.lastname: Maeda
authors.forename: Y
authors.initials: Y
authors.lastname: Motohashi
mesh_terms: D000328:Adult; D000513:Alpha Rhythm / Q000379:methods; D000704:Analysis of Variance; D001143:Arousal / Q000502:physiology; D001611:Beta Rhythm / Q000379:methods; D002940:Circadian Rhythm / Q000502:physiology*; D006801:Humans; D008297:Male; D011930:Reaction Time / Q000502:physiology*; D013826:Theta Rhythm / Q000379:methods; D013997:Time Factors