title: Effects of hypnagogic imagery on the event-related potential to external tone stimuli.
abstract: OBJECTIVE
  The purpose of this study was to examine the influence of hypnagogic imagery on the information processes of external tone stimuli during the sleep onset period with the use of event-related potentials.
  
  
  METHODS
  Event-related potentials to tone stimuli were compared between conditions with and without the experience of hypnagogic imagery. To control the arousal level when the tone was presented, a certain criterion named the electroencephalogram stage was used. Stimuli were presented at electroencephalogram stage 4, which was characterized by the appearance of a vertex sharp wave.
  
  
  METHODS
  Data were collected in the sleep laboratory at Hiroshima University.
  
  
  METHODS
  Eleven healthy university and graduate school students participated in the study.
  
  
  METHODS
  N/A.
  
  
  RESULTS
  Experiments were performed at night. Reaction times to tone stimuli were measured, and only trials with shorter reaction times than 5000 milliseconds were analyzed. Electroencephalograms were recorded from Fz, Cz, Pz, Oz, T5 and T6. There were no differences in reaction times and electroencephalogram spectra between the conditions of with and without hypnagogic imagery. These results indicated that the arousal levels were not different between the 2 conditions. On the other hand, the N550 amplitude of the event-related potentials in the imagery condition was lower than in the no-imagery condition.
  
  
  CONCLUSIONS
  The decrease in the N550 amplitude in the imagery condition showed that experiences of hypnagogic imagery exert some influence on the information processes of external tone stimuli. It is possible that the processing of hypnagogic imagery interferes with the processing of external stimuli, lowering the sensitivity to external stimuli.
authors.affiliation: Department of Behavioral Sciences, Faculty of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima, Japan.
authors.forename: Nanae
authors.initials: N
authors.lastname: Michida
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Hayashi
authors.forename: Tadao
authors.initials: T
authors.lastname: Hori
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods*; D000293:Adolescent; D000328:Adult; D004569:Electroencephalography; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D006212:Hallucinations / Q000175:diagnosis*; D006801:Humans; D008297:Male; D011930:Reaction Time