Light Deprivation Hinders Ability To Regulate Sleep-Wake Cycle

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Sleep Cycle

The amount of light exposure can have a profound effect on an individual's sleep pattern. Stronger light intensity enables noradrenergic locus coeruleus (LC) neurons, which regulate arousal, to function normally and, therefore, provide a circadian regulation of the sleep-wake cycle. Light deprivation, on the other hand, induces a loss of noradrenergic fibers which, in turn, throws a person's sleep-wake rhythm out of kilter.

The study, conducted by Monica McGonzalez, PhD, and Gary Aston-Jones, PhD, of the University of Pennsylvania, Philadelphia, focused on rats, that were maintained on a light-dark (LD) schedule or in constant darkness (DD) for three to four weeks, and treated with DSP-4, a neurotoxic agent specific for noradrenergic-LC projections. Vigilance states were analyzed before and three weeks after LC lesion. The DSP-4 lesion was verified by immunohistochemistry of noradrenergic fibers in the frontal cortex.

"DSP-4 decreased the amplitude of the sleep-wake rhythm in LD animals by significantly decreasing wakefulness and increasing sleep during the active period," the authors wrote. "However, DSP-4 had no effect on the sleep-wake cycle of DD animals. Moreover, DD itself decreased the amplitude of the sleep-wake cycle similar to that of the neurotoxic lesion of the noradrenergic system in LD animals.

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This study is particularly useful for those persons suffering from shift work, a circadian rhythm sleep disorder that occurs due to a work schedule that takes place during the normal sleep period. This schedule requires you to work when your body wants to sleep. Then you have to try to sleep when your body expects to be awake. The timing of when you sleep and wake is much different than what your internal body clock expects.

This sleep problem causes you to have trouble sleeping or to be severely tired. It is most often reported due to the night and early-morning shifts. These workers typically sleep one to four hours less than average. They also feel that the quality of their sleep is very poor. They do not feel refreshed when they wake up. This can hinder their performance at work. It can also make them less alert. This can put them at risk of an injury on the job.

One of the ways to cope with working an overnight shift is to adjust the lighting of your work space. Intense light exposure will enable your body to adjust to the "daytime-like" conditions in your office, and make you more alert and effective at your job. When it's time for you to go to sleep, take the steps necessary to make your bedroom dark. This will train your body to go to sleep at a bright time of day.

Sleep problems from shift work affect male and female workers of all age groups. Those who have unusual work hours are most likely to have it. Estimates are that two-to-five percent of the general population is affected, not including people who work early-morning shifts.

SLEEP is the official journal of the Associated Professional Sleep Societies, LLC, a joint venture of the American Academy of Sleep Medicine and the Sleep Research Society. www.SleepEducation.com

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