Internal body temp controls life's daily cycle.

• Position: Circadian Rhythm

Fluctuations in internal body temperature regulate the body's circadian rhythm, the 24-hour cycle that controls metabolism, sleep, and other bodily functions, according to a study published in Science.

A light-sensitive portion of the brain called the suprachiasmatic nucleus (SCN) remains the body's "master clock" that coordinates the daily cycle, but it does so indirectly SCN responds to light entering the eye, and so is sensitive to cycles of day and night. While light may be the trigger, researchers determined that SCN transforms that information into neural signals that set the body's temperature. These cyclic fluctuations in temperature then set the timing of cells and. ultimately, tissues and organs, to be active or inactive.

Scientists long have known that body temperature fluctuates in warm-blooded animals throughout the day on a 24-hour. or circadian, rhythm, but this study shows that temperature actually controls body cycles, maintains Joseph Takahashi, an investigator with the Howard Hughes Medical Institute, Chew Chase. Md.

"Small changes in body temperature can send a powerful signal to the clocks in our bodies. It takes only a small change in internal body temperature to synchronize cellular 'clocks throughout the body.

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