In a new study, published this week in the journal iScience, a team of researchers showed that Brazil reefs octopuses (Octopus insularis) have two different interrogation states that meet the behavioral criteria for sleep, namely ‘quiet sleep’ and ‘active sleep.’
Octopuses reef Brazil (Octopus insularis) you will have ‘quiet sleep’ and ‘active sleep’, with varying lengths and times. Image Credit: Medeiros et al., doi: 10.1016 / j.isci.2021.102223.
Scientists used to think that only amniotes (mammals, birds, and reptiles) had two sleep states.
A REM-like sleep state has recently been found in shellfish Sepia officinalis, a cephalopod relative of the octopus.
“That made us wonder if we were seeing evidence of two sleep states in octopuses as well,” said Dr. Sidarta Ribeiro, a researcher at the Brain Institute of the Federal University of Rio Grande do Norte.
“Octopuses have the most central nervous system of any invertebrate and are known to have high learning potential.”
To find out, Dr. Ribeiro and his colleagues captured video footage of him Octopus insularis 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’, animals change the color and texture of their 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,” said Dr. Ribeiro.
“The circle would be repeated at times between 30 and 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, both in ‘active’ and ‘quiet sleep’ states, showed that the animals needed strong stimulation to stimulate a behavioral response compared to the alert state. In other words, they were asleep.
“The change of sleep states seen in Octopus insularis it is very similar to ours, despite the great evolutionary distance between cephalopods and vertebrates, with an early separation of lines about 500 million years ago, ”said Sylvia Medeiros, a graduate student at the Federal University Brain Institute Rio Grande do Norte.
“If two different sleep states have alternated twice independently in the spine and invertebrates, what are the essential evolutionary pressures that shape this psychological process? ? ”
“The autonomic evolution in cephalopods of‘ active sleep ’similar to REM vertebrate sleep may reveal an emerging structure common to centralized celestial systems that reaches complexity. special. ”
The results also raise the potential for octopuses to experience something akin to dreaming.
“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, ”Medeiros said.
“If octopuses are indeed dreaming, they are unlikely to experience complex symbolic plots like us. ”
“’Active sleep’ in the octopus is short-lived – usually from a few seconds to one minute. If any dream is going on in this state, it should be more like small videoclips, or even gifs. “
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Sylvia Lima de Souza Medeiros et al. Cyclical change of silent and active sleep states in the octopus. iScience, published online March 25, 2021; doi: 10.1016 / j.isci.2021.102223