Circadian clock may be critical for remembering what you learn, Stanford resea...( The circadian rhythm that quietly pu...)

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 Stanford 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."

Though not known for their academic prowess, Siberian hamsters nonetheless normally develop what amounts to street smarts about their environment, as do all animals. But hamsters whose circadian system was disabled by a new technique Ruby and his colleagues developed consistently failed to demonstrate the same evidence of remembering their environment as hamsters with normally functioning circadian systems.

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 work is described in a paper published Oct. 1 online in the early edition of the Proceedings of the National Academy of Sciences. Ruby is lead author on the paper. Siberian hamsters, also known as dwarf hamsters, are about the size of a mouse.

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
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