If you're lucky enough to see a shallow-water octopus bedding down in a craggy nook off the coast of Okinawa Island — and you have the patience to wait about an hour after it falls asleep — you might see its dreams flash on the surface of its chameleon-like, color-changing skin. Although the creatures' brains are different enough from mammals that we can't say for certain whether they're actually dreaming, researchers have now mapped out a two-stage sleep cycle in octopuses. And, at first glance, their fitful sleep-flashes resemble the adorable twitching of a snoozing dog chasing rabbits in its sleep.
More than 500 million years of evolution has separated octopuses from humans, but the complex brains of sea creatures share a common feature with mammals when they sleep. Like mammals, they have distinct phases of sleep that are "active" and "quiet." But when octopuses fall into quiet periods of sleep, they will sometimes burst suddenly into a short, frenzied period of activity where their skin flashes colorfully.
