Octopuses, Like People, Seem To Have Active Stages Of Sleep, May Dream Octopuses have an "active" phase of sleep, the kind that might involve dreaming, but they probably don't have long, complicated dreams like people do.

Sleeping Octopuses May Have Dreams, But They're Probably Brief

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ARI SHAPIRO, HOST:

Octopuses are very different from us. But when they sleep, they may dream, according to new research. NPR's Nell Greenfieldboyce reports that the dreams probably don't last very long.

NELL GREENFIELDBOYCE, BYLINE: When octopuses sleep, their skin will sometimes flash with intense color changes. Their tentacles and suckers twitch. It looks like they're dreaming. Videos of this have gone viral.

SIDARTA RIBEIRO: This has been in front of everybody's eyes for all these years.

GREENFIELDBOYCE: Sidarta Ribeiro works at the Brain Institute of the Federal University of Rio Grande do Norte in Brazil. He wanted to study these supposedly dreaming cephalopods scientifically to make sure they were actually asleep.

RIBEIRO: Because people had not attempted to stimulate the animals during that state, one could always argue that it was active waking behavior.

GREENFIELDBOYCE: He and his colleagues videotaped sleeping octopuses and tested to see if they'd react to things like a swimming crab, a favorite food. Normally the octopuses would attack, but not while sleeping. What's more, their sleep had two distinct phases - a long, quiet phase when the animal stayed pale and motionless, followed by a brief active phase when their skin turned dark and their bodies moved. This cycle repeated every 30 minutes or so. The active phase was brief, less than a minute. So Ribeiro says if octopuses dream, they keep it short.

RIBEIRO: If they have some sort of inner life of, you know, representations of themselves, then it has to be something that fits within about a minute of behavioral sequences.

GREENFIELDBOYCE: He says mammals, including people, also have two sleep states that alternate in this way.

RIBEIRO: And then the question is, why is it so similar?

GREENFIELDBOYCE: After all, octopuses are separated from us by more than 500 million years of evolution, and their large, complex brains look nothing like our own. Nell Greenfieldboyce, NPR News.

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