title: Coherence of the electroencephalogram during the first sleep cycle.
abstract: OBJECTIVE
  The increasing amplitude of the electroencephalogram (EEG) during non-rapid eye movement sleep implies a progressive synchronization of neuronal activity. We sought to characterize the spatial relationship of cortical activity at different frequencies during the first sleep cycle, focusing on sleep stages 3 and 4 (slow wave sleep).
  
  
  METHODS
  Sleep EEGs were obtained at home from six adults using a portable recorder. Signal power and magnitude squared coherence were measured during the first sleep cycle. Spectra obtained from bipolar and common reference derivations were compared.
  
  
  RESULTS
  During slow wave sleep, signal power is highest in the delta frequency band and regional coherence below 5 Hz is broadly distributed. Although signal power in the alpha and sigma frequency bands is lower, peaks of regional coherence in those bands are similar to or higher than delta-band coherence. Regional coherence during slow wave sleep is differentially distributed with a 14 Hz component in central and posterior regions and a 10 Hz component in frontal and central regions.
  
  
  CONCLUSIONS
  Ten and 14 Hz rhythms are an essential component of slow wave sleep.
  
  
  CONCLUSIONS
  The interpretation of scalp EEG power and coherence spectra is limited by the lack of a satisfactory recording reference. However, conclusions can be made by comparing and contrasting results from both bipolar and common reference recordings.
authors.affiliation: Department of Neurology, Yale University School of Medicine, New Haven, CT 06520-8018, USA. robert.duckrow@yale.edu
authors.forename: R B
authors.initials: RB
authors.lastname: Duckrow
authors.forename: H P
authors.initials: HP
authors.lastname: Zaveri
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D004569:Electroencephalography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012894:Sleep Stages / Q000502:physiology*