The octopus has two alternate stages of sleep


Most of the time, when an octopus sleeps, its skin becomes pale and the muscles relax. However, from time to time, the animal will begin to lime, tighten the suction cup, move its eyes and change color. The explanation for this is now provided by a new study, according to which eight-armed cephalopods have active and passive sleep stages that are similar to humans from time to time. From the researchers’ point of view, it is also plausible that octopus dream during active sleep stages. The result is also interesting in relation to the development of sleep.

Pet owners can sometimes see their four-legged friend shaking their paws or making noise while sleeping. It has also been shown that birds and reptiles are known as REM sleep – the stages in which people dream the most. This stage is named Rapid Eye Movement which is unique. Studies in animals and humans suggest that REM is related to sleep learning processes and may play a role in coping with stress.

Sleep less excuse

Researchers, led by Sylvia Medeiros of the Federal University of Rio Grande do, Brazil, have now used video observations on four octopuses, which show that they also go through alternating sleep stages: most of their sleep For the time being, octaves are yellowish in color and massive. Immovable though, in between, they change their complexion and their muscles on the body and suction cups contract. Researchers report that an increase in eye movements can be seen during this phase.

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To verify that these active stages are actually sleeping and that the octopus just doesn’t wake up, the researchers presented them with visual stimuli: On a computer screen next to the aquarium, they played videos of crabs – one of theirs. Favorite foods – for them. If the octopus was awake, they were interested in the video, if they slept on the other side, they reacted without delay. In the case of the octopus, which was not enthusiastic about the video even while awake, the researchers instead knocked on the pool with increasing intensity. Here, it was also found that when the octopus slept, it required significantly stronger stimuli before reacting. This was even more true for active sleep stages than inactive ones. Apparently it was actually sleep.

What does an octopus dream of?

“It makes it even more interesting that this’ active sleep ‘is usually followed by a longer’ quiet sleep ‘- typically longer than six minutes. According to researchers’ observations, the cycle Repeats at intervals of about 30 to 40 minutes. Active sleep stages are usually very short – typically from a few seconds to a minute. Based on findings on REM sleep in humans and various vertebrates, researchers speculate that the octopus With active sleep experience something akin to a dream.

“It is not possible to confirm that they are dreaming because they cannot tell us, but our results suggest that during ‘active sleep’ the octopus may experience a state corresponding to REM sleep, which is the state , In which people dream the most, ”says Medeiros. As for the content of octopus dreams, she states: “If octopuses actually dream, it is unlikely that they will experience complex symbolic functions like we do.” The stages of active sleep are very short for this. “If people dream in this state, they are in the form of short video clips or even jiffs,” Medeiros says.

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See the development of sleep in a new way

The discovery of the octopus has various stages of sleep and may even shed new light on the development of sleep in dreams. “The change in sleep that we have seen in the octopus suggests that it is similar to ours despite the developmental distance between cephalopods and vertebrates,” says Medeiros. Given that the lines of development of the octopus and humans diverged around 500 million years ago, it seems unlikely that the various stages of sleep go back to their last common ancestor.

“If different sleep states actually develop twice independently of each other in vertebrates and invertebrates, then the question arises: what are the essential evolutionary forces that shape this physiological process?” “The independent development of active sleep in cephalopods corresponding to REM sleep in vertebrate animals may reflect a property that is common to all central nervous systems that reach a certain level of complexity.”

In future studies, researchers want to record neural data from cephalopods to understand what is going on during their sleep. They also want to clarify the role that sleep plays in animal metabolism, thinking and learning. “Dreaming in an octopus, like it happens in humans, is tempting to speculate,” says Ribeiro.

Quail: Sylvia Medeiros (Federal University of Rio Grande do Norte) et al., Iscience. doi: 10.1016 / j.isci.2021.102223

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