Minimal olfactory perception during sleep: why odor alarms will not work for humans

Sleep. 2004 May 1;27(3):402-5.


Study objectives: To examine olfactory arousal threshold during sleep in comparison to an auditory tone.

Design: 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.

Setting: Participants slept in individual rooms. Stimulus-delivery systems were operated from a separate room, where an experimenter observed physiologic recordings and behavioral responses.

Participants: Three healthy men and 3 women aged 20 to 25 years (mean, 22 years).

Interventions: Two odorants, peppermint and pyridine, at 4 concentrations were presented through nasal cannulas using an air-dilution olfactometer. Tones were played over a speaker.

Measurements: 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Arousal / physiology*
  • Electroencephalography
  • Electromyography
  • Female
  • Humans
  • Male
  • Odorants*
  • Sleep Stages / physiology
  • Sleep, REM / physiology*
  • Smell / physiology*