Color changes in sleep may indicate that octopuses dream – 06/30/2023 – Science

Scientific evidence is accumulating that octopuses not only dream, but have sleep phases comparable to those of humans. Studying 29 specimens while they slept, scientists at the Okinawa Institute of Science and Technology (OIST) in Japan found periods of “quiet sleep” and “active sleep”.

The latter are characterized by contractions of body parts and rapid changes in skin patterns and textures. The ability of cephalopods to change their color and texture in response to external impulses is well known, also for camouflage and communication purposes, but the phenomenon has now been studied in sleeping animals.

Encephalographic recordings performed in the OIST laboratory indicated that these active phases resemble the paradoxical sleep stage (rapid eye movement sleep – REM) observed in vertebrates, including humans, and associated with dream activity.

Analogies with REM sleep

The Okinawa team describes how they studied the sleep of 29 octopuses of the nocturnal species Octopus laqueus, which close their eyes in daylight and adopt the resting position associated with sleep.

Every 60 minutes, on average, the animals showed rapid changes in skin color, for about one minute, as well as body and eye movements and changes in respiratory rhythm. When the researchers tapped the aquariums, the octopuses showed different reactions, depending on whether they were awake, in the quiet phase, or in the active phase of sleep.

Then, when recording the neurological activity of the guinea pigs through probes, the team found in certain regions of the brain a strong correlation between the waking state and active sleep, confirming the analogy with the REM of vertebrates.

Furthermore, deprived of sleep for two days, the cephalopods exhibited a higher frequency of the active phase, entering it more quickly. This would indicate a homeostatic (self-regulatory) control in action, one of the key criteria for defining sleep.

An octopus and its nightmares

The research “Skin patterns and neural activity similar to wakefulness during octopus sleep” was published this Wednesday (28/06) in the scientific journal Nature. Its lead author, OIST professor Sam Reiter, told the British newspaper The Guardian that the results are consistent with the notion that octopuses dream, but do not prove it.

“We can associate certain dermal patterns, during wakefulness, with situations such as hunting, social and threat demonstrations, camouflage in different environments. We showed that these patterns reappear during active sleep”, he pointed out.

“So if we’re looking at something like dreams — and I repeat this is a possibility, which we didn’t prove in this study — they would resemble a pseudo random walk through different types of waking experiences.”

An alternative explanation, for example, would be that the animals are improving their camouflage patterns while they sleep, added Reiter.

This is not the first time that octopus sleep has made scientific headlines. In May, a study published on the preprint website BioRxiv reported as a octopus insularis male, apparently in a state of semi-sleep, sometimes left the resting position, showing behaviors associated with reaction to a predator.

Although discouraging hasty conclusions, even because it is an isolated specimen, the American researchers led by Eric A. Ramos suggested that the guinea pig could be “reacting to a negative episodic memory”. In other words: the octopus would be having a nightmare.

Too smart to end up on a restaurant plate?

Perhaps the nightmare is not without reason: worldwide, gastronomic consumption of octopus has grown from 180,000 tons in 1980 to more than 370,000 tons in 2019.

The new scientific revelations coincide with the ethical debate triggered by the announcement, in February of this year, of the opening of the first commercial octopus aquaculture farm in the Spanish region of Galicia. According to the company Nueva Pescanova, it is a “global milestone” in response to the very high demand for seafood.

In addition to reservations about the sustainability and viability of the project – previous attempts have resulted in high mortality, self-mutilation and cannibalism among captive animals – scientists and animal rights activists condemn the idea of ​​keeping cephalopods in captivity as unethical.

In 2022, the conclusion of a review of 300 scientific studies by the London School of Economics was that octopuses are sentient beings, capable of experiencing both distress and happiness.

In an interview with Reuters news agency, Raúl García, WWF coordinator for fisheries in Spain, said: “Octopuses are extremely intelligent and extremely curious. And it is well known that they are not happy in captive conditions.”

In the laboratory, cephalopods, endowed with extremely flexible bodies and eight independent tentacles covered by suction cups, have shown themselves to be capable of traversing intricate labyrinths and even handling tools, for example. In the absence of external stimuli, they even look for “creative” ways to occupy themselves.

Speaking on behalf of the NGO for the conservation of endangered species, García adds that any breeding initiative aimed at a high quality of life for octopuses, which tries to reproduce their natural habitat –solitary and at the bottom of the sea–, would probably be too costly to be profitable. .

At the aquaculture farm whose opening is scheduled for 2024, the animals must be slaughtered by slow freezing – a method classified as cruel. European Union laws on the welfare of slaughter animals do not apply to invertebrates. And although Spain, a major consumer of marine fauna, is tightening its animal protection legislation, an inclusion of octopuses is not foreseen.