How light became a therapy
The quest to understand light’s effect on biological rhythms dates back to the 1930s, when scientists first discovered a circadian system in plants.
Mounting evidence of the human body clock’s tendency to synchronize with the day-night cycle attracted more researchers to the budding field of chronobiology during the next several decades. But the research was largely abandoned in the 1970s after experiments in Germany indicated that social cues such as work schedules -- not sunrise and sunset -- were the chief pacemakers of a person’s sleep schedule.
In 1980, still convinced that light was the body’s core metronome, scientists at the National Institute of Mental Health discovered a link between light exposure and the suppression of melatonin, suggesting a biochemical basis for the waking effect of bright light.
The results put the light-dark theory back in vogue. “It influenced a lot of people to reconsider the role of the light-dark cycle and also the use of bright light to experimentally and perhaps therapeutically manipulate biological rhythms,” says Dr. Al Lewy, senior vice chairman of the department of psychiatry at Oregon Health and Science University, and one of the NIH scientists involved in the 1980 study.
The relationship between light, melatonin and a person’s sleep habits is orchestrated by a cluster of small structures in the brain called the suprachiasmatic nuclei, or SCN, located behind the eyes near the optic nerve. The onset or absence of light, relayed from the retinas via neurotransmitters, causes the firing rate of certain neurons in the SCN to change, which in turn affects the release of melatonin by the pineal gland. “
Thus, even the most dutiful midday sunbather may suffer from DSPS, Lewy says. “The key is to get the light as soon as you awaken. If you wait a few hours, it’s not going to be effective. There are a lot of people who dilly-dally around the house before they go outside.”
