Octopuses are known to sleep and change color as they do so. Now, a study published March 25 in the journal iScience discover that these color changes are part of two main sleep states: “active sleep” phase and “quiet sleep” phase. The researchers say the findings affect sleep evolution and may indicate that octopuses are able to experience something similar to dreams.
Scientists used to think that mammals and birds had only two sleep states. Recently, it has been shown that some reptiles also exhibit non-REM and REM sleep. A REM-like sleep state has also been reported in cuttlefish, a cephalopod relative of the octopus.
“That made us wonder if we were seeing evidence of two sleep states in octopuses, too,” said lead author Sidarta Ribeiro of the Federal Institute of Rio Grande do Norte, Norte, Brazil. “Octopuses have the most central nervous system of any invertebrate and are known to have high learning potential.”
To find out, the researchers captured video recordings of octopuses in the laboratory. They found that when they were ‘sound asleep’, the animals were still silent, with pale skin and eyes held to a slit. During active sleep, it was a different story. The animals changed the color and texture of the skin. They also moved their eyes as they contracted the suckers and the body with muscular cigarettes.
“What makes it more interesting is that this ‘active sleep’ usually occurs after a long ‘quiet sleep’ – usually longer than 6 minutes – and that there are certain times,” Ribeiro says.
The cycle was repeated at intervals of 30 to 40 minutes. To find out that these states actually represented sleep, the researchers measured the arousal threshold of the octopuses using visual and tactile stimulation tests. The results of these tests, both in the ‘active’ and ‘quiet sleep’ states, showed that the octopuses needed strong stimulation to stimulate a behavioral response compared to the alert state. In other words, they were asleep.
The findings have an interesting effect on octopuses and on the evolution of sleep. They also raise exciting new questions.
“The change of sleep states seen in the Octopus insularis looks very similar to ours, despite the great evolutionary distance between cephalopods and vertebrates, with an early separation of lines of about 500 million years. back, “said Sylvia Medeiros of the first author and graduate student of the Brain Institute of the Federal University of Rio Grande do Norte, Brazil.
“If two different sleep states have alternated twice independently in spine and invertebrates, what are the essential evolutionary pressures that shape this psychological process? ? ” she asked. “The independent evolution in cephalopods of‘ active sleep ’similar to REM vertebrate sleep may reveal an emerging structure common to centralized celestial systems that reaches a particular complexity. “
Medeiros also says the findings increase the ability for octopuses to experience something like a dream. “It is not possible to confirm that they are dreaming because they cannot tell us that, but our findings suggest that, during ‘active sleep’, the octopus may develop a state similar to REM sleep, that is the state in which people dream the most, “she says.” If octopuses are indeed dreaming, they are unlikely to experience complex symbolic plots as we do. ‘Active sleep’ in the octopus has a short duration – usually from a few seconds to one minute. If in this state is any dream. going forward, it should look more like small videoclips, or even gifs. “
In future studies, the researchers would like to record cloud data from cephalopods to better understand what happens when they sleep. They are also aware of the role of sleep in the metabolism, thinking and learning of animals.
“It’s a shame to think that, just like in humans, dreaming in the octopus could help respond to environmental challenges and encourage learning,” Ribeiro says. “Do octopuses have nightmares? Could octopuses’ dreams be written on their dynamic skin patterns? Could we read their dreams by measuring these changes? “
Information:
Medeiros SL de S, Paiva MMM de, Lopes PH, et al. Cyclical change of silent and active sleep states in the octopus. iScience. 2021; 0 (0). doi: 10.1016 / j.isci.2021.102223
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