Sleep Clears Way for New Learning

April 2, 2009 - Want to learn something new? Try getting a good night’s sleep or taking a long nap.

Sleep is now recognized as being critical for learning and memory, and now a new study in fruit flies offers clues as to why.

The research found that, in fruit flies at least, sleep weakens and even destroys existing synapses within the brain to make room for the creation of new ones.

Neurologists believe that the brain encodes memories and learning by creating these new synapses, which connect information-processing neurons throughout the central nervous system.

But seemingly conflicting theories exist about how sleep affects important synaptic connections; researcher Paul J. Shaw, PhD, of St. Louis’ Washington University tells WebMD.

“It is clear that if you don’t sleep, you don’t acquire information very well, you don’t process it very well and you don’t store it very well,” he says. “But we haven’t really known why that is. One theory is that sleep strengthens synapses and another is that it weakens them.”

People, Flies Need Sleep to Learn

Shaw says studying fruit flies in an effort to understand the human sleep-learning connection is less of a leap than one might think.

“We know that babies sleep a lot, and so do very young flies and that, like humans, if you deprive flies of sleep they do not learn,” he says. “If you had asked me 10 years ago if we would have found as many similarities between the fly and human brain, I would have said, ‘No way.'”

In earlier research, he and colleagues genetically altered fruit flies to make it possible to track the development of new synapses. They discovered that a very small number of neurons -- 16 out of about 200,000 -- are involved in the formation of new memories.

They also discovered that flies needed more sleep after social interaction experiments. When the flies slept, the number of new synapses formed during the social experiments declined and when the flies were deprived of sleep, the declines did not occur.

In their latest research, published in the April 3 issue of the journal Science, the researchers identify three specific genes critical to the sleep-learning connection.

One of these genes is the fly equivalent of a specific gene in humans linked to learning and memory, known as the serum response factor.

To Sleep, Perchance to Learn

The findings may help explain how sleep affects brain circuitry to clear the way for new learning, but Shaw does not believe they explain everything.

He says while some key synapses may be weakened or destroyed during sleep, others may be strengthened.

Sleep researcher Sara C. Mednick, PhD, tells WebMD that the fruit fly research offers important clues about how sleep may affect learning in humans.