Sleeping Cycles Reset by Doses of Bright Light

Carefully timed doses of bright light promise to be an effective tool in resetting the internal clocks of people troubled by jet lag and similar sleep disturbances, scientists reported Thursday.

A team of Boston researchers said tests of 14 men found that humans’ natural alarm clocks are far more sensitive to light than expected, and “can be reset to any desired phase by scheduled exposure to light for two to three days.”

Ordinarily, it can take nine days or longer for the body to adjust to a new sleep-wake cycle after long international flights or working a swing shift.

May Lead to Cures

In a study published in the journal Science, the scientists speculated that their technique may pave the way for “rapid and practical” treatments for people plagued by sleep disorders.

The research, directed by Dr. Charles Czeisler, expands on his 1986 study that showed light has a direct biological effect on sleep-wake patterns, rather than just indirectly throwing the cycle off by making it difficult to fall asleep.

The body’s internal clock, or “circadian pacemaker,” is located in the hypothalamus--the brain’s regulatory center for sleep and other vital activities. Nerves from the eye’s retina are linked to the hypothalamus, and Czeisler theorizes that most resetting action comes from light’s impact on that system.