Octopuses change colour based on sleep cycle

When sleeping, octopuses change colour, and now a study, published in iScience, shows that the colours represent octopus sleep cycles.

The team, led by Sylvia Lima de Souza Medieros from the Federal University of Rio Grande do Notre, Brazil, found that the colours change over two major alternating sleep states: REM and non-REM.

Previously, it was though that only mammals and birds had these two sleep states, but recently it was shown that it was also present in an octopus cousin, the cuttlefish.

“That led us to wonder whether we might see evidence of two sleep states in octopuses, too,” says Sidarta Ribeiro of the Brain Institute of the Federal University of Rio Grande do Norte.

“Octopuses have the most centralized nervous system of any invertebrate and are known to have a high learning capacity.”

The team filmed four Octopus insularis while they were sleeping and found that they were pale blue during non-REM ‘quiet’ sleep, and dynamically ‘pulsed’ in colour during REM ‘active’ sleep, while also twitching their eyes, body and suckers.

An octopus in quiet sleep and active sleep. Credit: Sylvia S L Madeiros

Cephalopods are very different from humans evolutionarily, diverging around 500 million years ago, so it is possible we both evolved a similar sleeping pattern individually, explains Mederios. This means that sleep patterns have an evolutionary advantage that is yet to be established. It could even suggest that octopuses dream, too.

“If octopuses indeed dream, it is unlikely that they experience complex symbolic plots like we do,” says Medieros.

“‘Active sleep’ in the octopus has a very short duration–typically from a few seconds to one minute.

“If during this state there is any dreaming going on, it should be more like small videoclips, or even gifs.”

Of course, while the idea of an octopus technicoloured dream coat is mesmeric, it’s very difficult to answer what is going on in their heads.

“It is tempting to speculate that, just like in humans, dreaming in the octopus may help to adapt to environmental challenges and promote learning,” Ribeiro says.

“Do octopuses have nightmares? Could octopuses’ dreams be inscribed on their dynamic skin patterns? Could we learn to read their dreams by quantifying these changes?”

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More on octopuses

• How the octopus got its smarts
• Taste by touch is all in the suckers
• How an octopus can “see” with its skin