Key study - Czeisler et al (1990)

Key study - Czeisler et al (1990)

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  • AimTo find out whether disturbances in the sleep-wake cycle created by working at night could be prevented by a treatment program of exposure to bright light during the night, and darkness during the day.
  • Method and procedure8 young men (aged 22-29) who were not used to shift work were asked to arrive at 23:45 for 6 nights of sedentary, office-based shift-work. They were asked not to drink caffeine or alcohol and this was checked by urine analysis.
  • One of the participants worked in ordinary indoor light (150 lux).
  • The other group were exposed to extreme bright light (7000 lux - equivalent to early morning light) during this nightshift and then instructed to go home and sleep in complete darkness from 9-5pm.
  • The core body temperature of participants (which falls during sleep) was recorded over the course of the research for both groups. They were given cognitive tests and self-report mood and alertness questionnaires.
  • ResultsMean temperatures of the group with ordinary light fell during the night, whereas after 4 days the temperature of the group exposed to bright light fell at midday. 
  • The 'bright light' group had successfully adapted their circadian rhythms to the night-time work schedule, whereas the 'ordinary light' group had not (they continued experiencing the sleep pattern of the circadian rhythm at night when working)
  • The group exposed to the bright light showed improved results on all tests after 2-3 days, including improved mood, alertness, concentration, overall cognitive ability as well as shift in urinary excretion rate.
  • ConclusionDisturbances in the sleep-wake cycle, including associated declines in alertness, performance and quality of sleep, can be treated effectively with scheduled exposure to bright light at night and darkness during the day.
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