title: Examining initial sleep onset in primary insomnia: a case-control study using 4-second epochs.
abstract: OBJECTIVE
  To explore the sleep onset process in primary insomnia patients, new rules for scoring 4-second epochs were implemented to score sleep and artifacts during initial sleep onset. Conventional scorings in 20-second and 60-second epochs were also obtained.
  
  
  METHODS
  The start of the initial 60-second epoch of stage 1 was used to define "time zero" (t0). Sleep onset periods from 11 patients and 11 individually age- and sex-matched controls spanned from 5 minutes before t0 through 29 minutes after t0. Using the new rules, the periods were scored blind to group assignment. This t0 time-referenced the data analysis to one plausible midpoint in the sleep onset process. In parallel, latencies were time-referenced from good night time.
  
  
  RESULTS
  Reliability in scoring sleep and artifacts was adequate (kappa = 0.68 & 0.63, respectively, p <0.001). Group differences in sleep latencies were marginal in 60-second and 20-second scoring but significant with a definition of 4-second sleep latency. Patients had more 4-second epochs scored as awake (Mantel-Haenszel chi2 = 271, d.f. = 1, p <0.001) and containing artifact (M-H chi2 = 143, p <0.001). Patients took longer to achieve 30 continuous 4-second epochs of NREM sleep (Breslow chi2 = 4.03, d.f. = 1, p = 0.045) after t0. Patients accumulated sleep more slowly with all 3 scoring rules after t0. A slower rate of accumulating sleep after t0 was detected only with the 4-second scoring (p = 0.047).
  
  
  CONCLUSIONS
  Evidence was present for momentary state-switching instabilities in the patients during the initial sleep onset process. Using rules for scoring small epochs may reveal such instabilities more readily than traditional scoring methods.
authors.affiliation: University of Pittsburgh, Department of Psychiatry, Pittsburgh, PA, USA. moulde@upmc.edu
authors.forename: Douglas E
authors.initials: DE
authors.lastname: Moul
authors.forename: Anne
authors.initials: A
authors.lastname: Germain
authors.forename: J David
authors.initials: JD
authors.lastname: Cashmere
authors.forename: Michael
authors.initials: M
authors.lastname: Quigley
authors.forename: Jean M
authors.initials: JM
authors.lastname: Miewald
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Buysse
mesh_terms: D016022:Case-Control Studies; D016009:Chi-Square Distribution; D005260:Female; D006801:Humans; D008297:Male; D017286:Polysomnography / Q000379:methods*; D015203:Reproducibility of Results; D007319:Sleep Initiation and Maintenance Disorders / Q000175:diagnosis*; D012894:Sleep Stages; D014851:Wakefulness