Octopuses, like humans, have different stages of sleep and even seem to dream

The world’s most intelligent invertebrates, whose repertoire of complex behaviors includes cheating, the use of tools, and the ability to play, may already have added a new achievement to their curriculum: dreaming.

“Yes, octopuses seem to be dreaming. And you can see it on your skin, ”says neuroscientist Sidarta Ribeiro, researcher at the Brain Institute of the UFRN (Federal University of Rio Grande do Norte) and one of the authors of a new study on the subject that has just been published in the journal iScience.

With the help of four “volunteers” of the species Octopus insularis, which are common in places on the Brazilian coast such as the island of Fernando de Noronha, Ribeiro and his colleagues received detailed data on the various rest and wake cycles typical for these mollusks. They were able to demonstrate the existence of an “active sleep state” in which the animals are completely separated from what is happening around them, but show eye movements, muscle spasms and sudden changes in skin color.

These are physiological changes very similar to those that occur during dreams of vertebrates such as humans (with the exception of color changes, of course). It is a strong indication that something would happen in the octopus nervous system that is comparable to the dream we experience every night.

However, it was no joke to come to this conclusion. The neuroscientist at UFRN, one of the world’s foremost specialists in the neurobiology of dreams, says he has had a desire to study octopus since receiving his doctorate in 2000. “We started from scratch, we took several paths, but we finally learned how to create and study them. “

A long-term collaboration with Tatiana Leite, an octopus specialist at UFRN and now at UFSC (Federal University of Santa Catarina), is essential for this. “One day Tati called me to let me know that she had found the right person to lead the project, and it was. Sylvia Medeiros is a biologist with experience of researching squid in the natural environment, a diver who is very good at catching and handling animals, ”he says. Both sign the paper.

With a size of about 15 cm (excluding tentacles), O. vulgaris is a small generalist predator with a predilection for crustaceans and other small invertebrates. As the UFRN team shows in the study, its behavioral repertoire is diverse and not yet fully understood.

The animal does things like being calm, with only one eye that moves, or the so-called “half and half”, in which the octopus divides the body exactly in the middle with a light and a dark band (which he with special skin and muscle cells).

However, a detailed analysis of the octopus quartet in the laboratory revealed the presence of two states that are really similar to sleep. In one of them, the so-called “peaceful sleep”, the animal fades, its pupils constrict until they seem to be nothing but a squeak and it hardly moves. There is also active sleep, which has already been described above. The most interesting thing is that in tests done to wake the sleeping squids with visual stimuli and make the aquariums vibrate, active sleep appears to be “deeper” than peaceful sleep – stronger stimuli are required to keep the animals in first to wake case.

“It’s very impressive. During active sleep, the pupils do not open completely, but are deformed by movement and sometimes open a little, but even then the animals do not wake up. It’s important to remember that octopuses also have a photo reception [detecção de luz] The lack of responsiveness then occurs on the skin during active sleep, although the animal is reached through a lot of stimulation, ”explains Ribeiro.

The researchers also showed the existence of relatively well-defined cycles of duration and alternation between forms of sleep. Episodes of peaceful sleep are usually longer than those of active sleep (an average of 7 minutes versus 40 seconds). In addition, longer phases of peaceful sleep tended to be followed by phases of active sleep.

But what ultimately happens in the mollusc’s nervous system during periods of busy sleep? The vertebrate analogy – we already know that mammals, birds, and even reptiles dream – suggests that switching between sleep states is very important for learning and problem solving. In mammals, these processes help regulate the plasticity of synapses (connections between neurons), that is, the flexibility with which brain cells “speak” to one another.

“It is tempting to speculate that similar mechanisms are at work in octopuses,” says Ribeiro, especially when one takes into account the learning flexibility typical of animals.

The problem is to measure this directly. “When I first started doing research, I thought I could record data on the animals’ neurons using methods similar to what I use on mice, but it was a mistake. So far we have failed miserably when trying to stabilize the animals’ electrodes. Everything is soft and slippery and they won’t accept any attempt to immobilize them. There are simply no bones to attach a screw or resin to. Problem! “Laments, the neuroscientist.

Although there is no view that this type of measurement is possible, the group should continue to use other methods to study behavioral and molecular biological aspects of the species.

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