Do Octopuses Dream?

The cephalopods have two separate sleep states, new study finds.

Octopuses change colors while they sleep. Douglas Klug / Getty Images

Octopuses are visually exciting when they sleep. While humans might toss and turn, octopuses put on a light show. They change colors and patterns while they rest.

New research finds that octopuses have two major alternating sleep states — quiet sleep and active sleep — and the colors suggest when they’re experiencing something that may be like dreaming.

“During ‘quiet sleep’ the animal is very quiet, with pale skin and the eye pupil is contracted to a slit. The second state is an ‘active sleep,’ in which the animals dynamically change the skin color and texture and move both eyes while contracting the suckers and the body, with muscular twitches,” senior author Sidarta Ribeiro of the Brain Institute of the Federal University of Rio Grande do Norte, Brazil, tells Treehugger.

Active sleep typically occurs after a long quiet sleep period, usually at least six minutes or more. And it usually repeats every 26 to 39 minutes.

Scientists previously believed that only mammals and birds had two distinct states of sleep: non-REM and REM sleep. REM sleep is when most dreams usually happen.

Then researchers found some reptiles have both REM and non-REM sleep. And a REM-like state was discovered in cuttlefish, which are also cephalopods like the octopus.

"That led us to wonder whether we might see evidence of two sleep states in octopuses, too," says Ribeiro. "Octopuses have the most centralized nervous system of any invertebrate and are known to have a high learning capacity."

In order to find out, the researchers recorded videos of octopuses in the lab and developed a visual and mechanical stimulation test to measure the animals’ arousal threshold at different points across the wake-sleep cycle.

“The results show that in both sleep states the octopuses needed a strong stimulus to evoke a behavioral response, in comparison with the alert state, during which animals are sensitive to very weak stimuli,” first author and graduate student Sylvia Medeiros of the Brain Institute of the Federal University of Rio Grande do Norte, Brazil, tells Treehugger.

The results of their research were published in the journal iScience.

Are Sleeping Octopuses Dreaming?

Earlier research found that when cephalopods rest, their cells that contain pigment (chromatophores) become active.

In the video above, for example, David Scheel, a professor of marine biology at Alaska Pacific University in Anchorage, narrates as a sleeping octopus named Heidi changes colors in her tank.

Scheel says that if Heidi's dreaming, her changing colors can suggest the subjects of her dreams.

But do octopuses really experience something like dreams?

“It is not possible to affirm that they are dreaming because they cannot tell us that, but our results suggest that during ‘active sleep’ the octopus experiences a state analogous to REM sleep, which is the state during which humans dream the most,” Medeiros says.

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

The findings have interesting implications for understanding octopus cognition, sleep evolution, and a possible relationship between sleep and cognition in the cephalopods, the researchers say.

They’d like to continue research in order to better understand what exactly is happening when the animals are sleeping.

"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?"

View Article Sources
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