title: Direct effects of light on alertness, vigilance, and the waking electroencephalogram in humans depend on prior light history.
abstract: OBJECTIVE
  Light can induce an acute alerting response in humans; however, it is unknown whether the magnitude of this response is simply a function of the absolute illuminance of the light itself, or whether it depends on illuminance history preceding the stimulus. Here, we compared the effects of illuminance history on the alerting response to a subsequent light stimulus.
  
  
  METHODS
  A randomized, crossover design was used to compare the effect of two illuminance histories (1 lux vs. 90 lux) on the alerting response to a 6.5-h 90-lux light stimulus during the biological night.
  
  
  METHODS
  Intensive Physiologic Monitoring Unit, Brigham and Women's Hospital, Boston, MA.
  
  
  METHODS
  Fourteen healthy young adults (6 F; 23.5 ± 2.9 years).
  
  
  METHODS
  Participants were administered two 6.5-h light exposures (LE) of 90 lux during the biological night. For 3 days prior to each LE, participants were exposed to either 1 lux or 90 lux during the wake episode.
  
  
  RESULTS
  The alerting response to light was assessed using subjective sleepiness ratings, lapses of attention, and reaction times as measured with an auditory psychomotor vigilance task, as well as power density in the delta/theta range of the waking EEG. The alerting response to light was greater and lasted longer when the LE followed exposure to 1 lux compared to 90 lux light.
  
  
  CONCLUSIONS
  The magnitude and duration of the alerting effect of light at night depends on the illuminance history and appears to be subject to sensitization and adaptation.
authors.affiliation: Division of Sleep Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA. amchang@rics.bwh.harvard.edu
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Chang
authors.forename: Frank A J L
authors.initials: FA
authors.lastname: Scheer
authors.forename: Charles A
authors.initials: CA
authors.lastname: Czeisler
authors.forename: Daniel
authors.initials: D
authors.lastname: Aeschbach
mesh_terms: D001143:Arousal / Q000528:radiation effects*; D001288:Attention / Q000528:radiation effects; D018592:Cross-Over Studies; D004569:Electroencephalography; D005260:Female; D006801:Humans; D008027:Light; D008297:Male; D008550:Melatonin / Q000097:blood / Q000502:physiology; D011597:Psychomotor Performance / Q000528:radiation effects; D011930:Reaction Time; D014851:Wakefulness / Q000528:radiation effects*; D055815:Young Adult
chemical_list: D008550:Melatonin
keywords: Light history; alertness and performance; light exposure
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