The body's clock may lose track of time during winter hibernation, scientists have found in a species of hamster.  
The genes responsible for regulating circadian rhythms in the brain normally follow a 24-hour cycle, with their activity waxing and waning in step with day and night. But what happens during hibernation?  
Brain activity resembles that of deep slumber, and the body slows its metabolism to a crawl. The internal temperature of arctic ground squirrels, for instance, can plummet below freezing. It's thought that hibernation evolved from sleep as a way to save energy during lean winter months.  
Some studies have hinted that factors such as body temperature continue to oscillate up and down in a daily cycle during this winter period, although not nearly so much as during normal conditions. But no one had tapped directly into the brain or looked at the genes that control the body clock to see what was happening there.