Two Systems, One Sleep


Recently, scientists have come to recognize that sleep is regulated by two entirely different systems. The knowledge that we have two roughly parallel forces guiding our need for sleep has opened the bedroom door to multiple ways of treating insomnia.

One force is the sleep homeostat. This functions like a drive that “builds up during wakefulness in pretty much a linear fashion and is discharged when you sleep,” explains Arthur J. Spielman, associate director of the Center for Sleep Medicine at New York Presbyterian-Cornell Medical College. The homeostatic pressure to sleep depends not only on how long you are awake but on how active you are while awake.

But if you build up a need for sleep in a linear fashion, one would think you’d get sleepier as the day proceeds. It doesn’t happen quite that way. Enter circadian rhythm, the body’s biological clock. The circadian system is tied, albeit imperfectly, to cycles of light and dark. We have dedicated sensors on the retina that deliver the daytime/nighttime message directly to the pineal gland tucked deep inside the brain. In response to darkness, this tiny nodule of brain tissue produces the sleep-inducing hormone melatonin, broadcasting the sandman’s message to brain areas that govern everything from body temperature to protein synthesis to hormone production to alertness.

Psychology Today Magazine, Nov/Dec 2003

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