Circadian Rhythm Affects Memory

Jim Dawson, Inside Science News Service,

LiveScience.com, 10/13/08

Most people become aware of their internal circadian

clock when they cross several time zones and experience

jet lag, but scientists have known for decades that the

rhythm of the internal human clock regulates almost every

biological system, from blood pressure to sex drive.

Now researchers at Stanford University have shown that

when the circadian system breaks down, so does

memory. In a paper published in the Proceedings of the

National Academy of Sciences, biologist Norman Ruby

found that hamsters with disabled circadian systems

were, unlike "normal" hamsters, unable to remember their

environment.

"They can't remember anything," Ruby said of the

hamsters.

Scientists have long suspected that learning and memory

might be related to different levels of brain function, or

alertness, that change over a day due to normal circadian

rhythms, but it hadn't been shown that the circadian

system is crucial to learning and memory. Ruby found that

learning and memory appears to hinge on the amount of

the neurochemical GABA, which is found in the brains of

all animals. GABA, which inhibits brain activity, is

released rhythmically by the body in accordance to the

circadian clock controlling sleep and wake cycles.

When Ruby disabled the hamsters' clocks by manipulating

their exposure to light the hamsters experienced

chronically high levels of GABA and essentially lost their

ability to remember. The findings have implications for

people with Down syndrome, who grow up with what

amounts to an over-inhibited brain, according to the

research. It also may have implications for the decline in

memory that older adults often experience.

"In aging humans, one of the big things that happens is 

the circadian system starts to degrade and break down,"

Ruby said. "It might be that the degradation of circadian

rhythms in elderly people may contribute to their short-

term memory problems."

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