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Animal studies show that sleep dramatically enhances changes in brain connections during a period of early development. Researchers at the University of California, San Francisco, examined the effect of sleep on brain plasticity in young cats that had just experienced an environmental challenge. The animals that were allowed to sleep for six hours after the stimulation developed twice the amount of brain change, compared to cats kept awake afterward.

"This is the first direct evidence that sleep modifies the effect of environmental stimuli on the development of new brain connections," said Marcos G. Frank, Ph.D. The finding has broader implications for plasticity in the brains of adult animals and people.

"I think it's likely to be true that other areas of the brain, higher areas of the brain, have their critical (developmental) periods later in life," said the study's senior author Michael P. Stryker, Ph.D., "and some of them, in the highest areas, the critical periods never close until senility."¹²

What's more, the amount of plasticity (connections between nerve cells) in the brain depends on the amount of deep sleep, which is indicated by large slow brain waves. This is the sleep that a person falls into when they first go to sleep, and accounts for half of sleep time in young animals and human babies, (who get up to three times more sleep than adults). Stryker said this is precisely the time in life when the brain reorganizes its connections to attain the perfect precision it needs as an adult.