In tests with hamsters, they found that a functioning circadian system is critical to the rodents' ability to memorize what they've learned. Without it, they "can't remember anything," said lead author and biologist Norman Ruby.

Hamsters whose circadian system was disabled consistently failed to remember their environment. The loss of the circadian system resulted in constant production of a neurochemical called GABA, which acts to inhibit brain activity, the researcher said. When they were given a chemical that blocks GABA from binding to brain synapses, the circadian system-deficient hamsters learned as well as their normal counterparts.

"What our data are showing is that these animals still performed terribly on a simple learning task, even though they're getting loads of sleep. What this says is that the circadian system really is necessary for something that is deeply important: learning," Ruby said in a Stanford news release.

The study, believed to be the first to show that a loss of the circadian system affects learning, was published in this week's online issue of the Proceedings of the National Academy of Sciences.

The findings may have implications for diseases that feature learning or memory deficits, such as Down syndrome or Alzheimer's disease, and for age-related decline in memory function.

"In aging humans, one of the big things that happens is the circadian system starts to degrade and break down," Ruby said. "When you get older, of course, a lot of things break down, but if the circadian system is a player in memory function, it might be that the degradation of circadian rhythms in elderly people may contribute to their short-term memory problems."

"There are a lot of things that could cause memory to fail, but the idea would be that in terms of developing therapeutic treatments, here is a new angle," Ruby added.