Health Watch -- Body Clock

Health Watch is a Public Service of the Office of News and Publications and is intended to provide general information only and should not replace the advice of a medical professional. You should contact your physician if you have questions about any of these topics.

How does your brain go about setting your body clock?

The sun gives us good clues about what time of day it is - if the sun is down, it's dark and time to sleep. If the sun is out, it's day and time to be active. But researchers at UT Southwestern Medical Center at Dallas have found that it may be more complicated than that.

For mammals - including humans - circadian rhythms are heavily influenced by the presence or absence of light. The brain's schedule setter is an area called the suprachiasmatic nucleus, or SCN. This area controls whether you're awake or sleepy and whether or not you're hungry. It's turned on during the day and off at night by a factor scientists call CLOCK, which is triggered by light and dark.

UT Southwestern scientists found that there's another protein in a different part of the brain that also has an effect on the SCN. This protein is found in the forebrain, in an area that responds to sensory input like sound, smell and touch. It helps the body respond to other cues for determining when it's time to sleep.

Normal mice are nocturnal. They feed and are active during the night. Mice lacking the gene for this other protein were able to keep to their usual schedule when they were fed at night. But if they were fed during the day, they had difficulty adapting. Meanwhile, mice that had the gene soon adapted their schedule so they were eating and active during the day and sleeping at night.

This knowledge could be important for understanding human sleep behavior and for helping people adapt to changes in their normal sleep cycle, such as when they have to work odd shifts or change time zones.