Public Release: 

Exposure to light and sleep pattern alteration

American Academy of Neurology

DENVER, CO- Each person's circadian rhythm, or biological clock, influences when we are tired, hungry, more or less sensitive to drugs and other stimuli, and even cues the secretion of hormones throughout each 24-hour period. In a study presented at the annual meeting of the American Academy of Neurology, researchers demonstrate the degree to which light exposure, as well as alterations in sleep patterns, can affect the timing of the circadian clock.

Recent studies have shown that both the intensity and the timing of light are important to determining the magnitude of shifts in the circadian clock. "We were interested to know more about the response of the human biological clock to varying durations of light pulses," says study author Samir Bangalore, of Northwestern University Medical School in Chicago, IL.

For the study, 10 men and 22 women, average age 29, were admitted for two stays at a clinical research center, each lasting four nights and three days. On the first night, subjects maintained a constant daytime routine and slept for eight hours in the dark at their usual bedtime. Each of the following nights, subjects were awoken and exposed to varying intensities and durations (one, two, or three hours) of light, with a control group simply awakened for four hours each night. Circadian rhythms were measured by fluctuations in core body temperature and in levels of serum melatonin, a hormone believed to play a role in the circadian rhythm.

According to Balgalore, "Our results indicate that a single pulse of bright light lasting just two to three hours is sufficient to delay human circadian rhythms." Furthermore, disruptions in sleep timing can also produce small rhythm delays. Together, these results show that duration of light exposure, in addition to light intensity and alterations in sleep patterns, can affect the timing of the circadian clock.


The American Academy of Neurology, an association of more than 18,000 neurologists and neuroscience professionals, is dedicated to improving patient care through education and research.

For more information about the American Academy of Neurology, visit its web site at

EDITORS NOTE: Samir Bangalore will present the research at the American Academy of Neurology's 54th Annual Meeting in Denver, Colo., during a poster presentation on Thursday, April 18, 2002, at 3:00 p.m. in Exhibit Hall C of the Colorado Convention Center. He will be available to answer media questions during a briefing on Thursday, April 18, 2002 from 11:00 a.m. - 12:00 p.m. in the AAN Media Room, Lobby C, Room 208 of the Colorado Convention Center.

For more information contact:
Kathy Stone, 651-695-2763,
April 13-20, 303-228-8450
Cheryl Alementi, 651-695-2737,

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