title: Minimal olfactory perception during sleep: why odor alarms will not work for humans.
abstract: OBJECTIVE
  To examine olfactory arousal threshold during sleep in comparison to an auditory tone.
  
  
  METHODS
  On night 1, participants rated odor intensity when awake and experienced olfactory stimuli during stage 1 sleep. Night 2 involved stage 2, stage 4, and rapid-eye-movement (REM) sleep trials using the "staircase" threshold-detection method. Electroencephalogram, electrooculogram, electromyogram, electrocardiogram, and respiration were recorded along with behavioral response. An 800-Hz tone was given on trials when odors failed to arouse.
  
  
  METHODS
  Participants slept in individual rooms. Stimulus-delivery systems were operated from a separate room, where an experimenter observed physiologic recordings and behavioral responses.
  
  
  METHODS
  Three healthy men and 3 women aged 20 to 25 years (mean, 22 years).
  
  
  METHODS
  Two odorants, peppermint and pyridine, at 4 concentrations were presented through nasal cannulas using an air-dilution olfactometer. Tones were played over a speaker.
  
  
  METHODS
  Behavioral (button press and oral) responses, electroencephalographic activation, and changes in breathing and heart rate were assessed.
  
  
  RESULTS
  Participants responded to odors on 92% of stage 1 sleep trials. Peppermint was ineffective in stages 2, 4, and REM sleep. Pyridine produced behavioral threshold on 45% of stage 2 trials, none in stage 4, and one third of REM sleep trials. Tones were effective on at least 75% of trials. Heart rate increased significantly only following behavioral responses to odors or tones across sleep stages.
  
  
  CONCLUSIONS
  The data indicate that human olfaction is not reliably capable of alerting a sleeper.
authors.affiliation: Department of Psychiatry and Human Behavior, Sleep Research Laboratory, Brown Medical School/Bradley Hospital, Providence, RI 02906, USA. mary_carskadon@brown.edu
authors.forename: Mary A
authors.initials: MA
authors.lastname: Carskadon
authors.forename: Rachel S
authors.initials: RS
authors.lastname: Herz
mesh_terms: D000328:Adult; D001143:Arousal / Q000502:physiology*; D004569:Electroencephalography; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D009812:Odorants; D012894:Sleep Stages / Q000502:physiology; D012895:Sleep, REM / Q000502:physiology*; D012903:Smell / Q000502:physiology*