Sleep is a sometime thing among cetaceans

July 08, 2005|By New York Times News Service

Sleep is vital to the development of brain and body. That truism comes from basic observations about humans and other mammals, that sleep is maximized at birth and declines gradually until adulthood.

But a new finding threatens to throw that common wisdom out the window. Researchers have discovered that some whales and dolphins don't sleep after birth. Both newborns and their mothers stay continuously active for about a month and then gradually build up their sleep to normal adult levels after four or five months.

"What's going on is very different than any animal ever encountered," said Dr. Jerome Siegel, a professor of psychiatry at UCLA and an author of a paper describing the finding in the journal Nature. Siegel and his colleagues studied newborn killer whales and bottlenose dolphins, recording the cetaceans' activities in pools at Sea World in San Diego and in an aquarium in Russia.

Dolphins had already been known to exhibit unusual resting behavior: They sleep with one eye open. Dolphins have also never been shown to exhibit rapid-eye-movement sleep, Siegel said.

Why don't these animals need REM sleep? "It may be that REM sleep has a function for stimulating the brain, and non-REM sleep is more of a rest state," he said. "And because dolphins never have a brain in a rest state, there's no need for it."

"But how they do without sleep in general," he added, "I don't have a clue."

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