Circadian Clock Could Be Critical For Remembering What You Learn

The circadian rhythm that quietly pulses inside us all, guiding our daily cycle from sleep to wakefulness and back to sleep again, may be doing much more than just that simple metronomic task, according to researchers. Working with Siberian hamsters, biologist Norman Ruby has shown that having a functioning circadian system is critical to the hamsters' ability to remember what they have learned. Without it, he said, "They can't remember anything."

Until now, it has never been shown that the circadian system is crucial to learning and memory. The finding has implications for diseases that include problems with learning or memory deficits, such as Down syndrome or Alzheimer's disease.

The change in learning retention appears to hinge on the amount of a neurochemical called GABA, which acts to inhibit brain activity. All mammal brains function according to the balance between neurochemicals that excite the brain and those that calm it. The circadian clock controls the daily cycle of sleep and wakefulness by inhibiting different parts of the brain by releasing GABA.

But if the hippocampus - the part of the brain where memories are stored - is overly inhibited, then the circuits responsible for memory storage don't function properly. "Those circuits need to be excited to strengthen and encode the memories at a molecular level," Ruby said.

"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," he said. "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.