The octopus is an extraordinary creature, and not just because of its eight limbs, three hearts, blue blood, ink jets, camouflage ability, and the tragic fact that it dies after mating.
A study by researchers in Brazil published on Thursday shows that this animal, already considered perhaps the most intelligent invertebrate, experiences two great alternative sleep states eerily similar to those of humans, and could even dream.
The findings, the researchers said, provide new evidence that the octopus possesses a complex and sophisticated neurobiology that underlies an equally sophisticated behavioral repertoire, while offering a broader view of the evolution of sleep, a crucial biological function.
Octopuses were previously known to experience sleep and change color while sleeping. In the new study, the researchers observed a species called Octopus insularis in a laboratory setting. They found that these color changes are associated with two different sleep states: “quiet sleep” and “active sleep.”
During “quiet sleep”, the octopus remains still, with pale skin and the pupils of the eyes contracted into a slit. During “active sleep”, he dynamically changes the color and texture of his skin and moves both eyes while contracting his suction cups and his body, with muscle spasms.
A repeated cycle was observed during sleep. The “quiet sleep” lasted approximately seven minutes. The subsequent “active sleep” generally lasted less than a minute.
This cycle appears analogous, the researchers said, to the alternating sleep state of “rapid eye movement” or REM, and “non-rapid eye movement” or non-REM, experienced by people, as well as other mammals, birds and reptiles. .
Vivid dreams occur during REM sleep, when a person’s eyes move rapidly, breathing becomes irregular, heart rate increases, and muscles become paralyzed from representing dreams. Non-REM sleep presents deeper sleep and fewer dreams.
Study lead author Sylvia Medeiros said the findings suggest that octopuses may be dreaming or experiencing something similar.
“If octopuses really dream, they are unlikely to experience complex symbolic plots like we do,” said Medeiros, a neuroscience doctoral student at the Brain Institute of the Federal University of Rio Grande do Norte.
“The ‘active sleep’ in the octopus has a very short duration, typically a few seconds to a minute. If there is a dream during this state, it should be more like little video clips, or even GIFs, ”added Medeiros.
Scientists seek a greater understanding of the origins and evolution of sleep.
Because the last common ancestor of vertebrates, including humans, and cephalopods, including octopuses, lived more than 500 million years ago, it seems unlikely that their similar sleep patterns were established before their evolutionary divergence, they said. researchers.
That would mean, they added, that this similar sleep pattern arose independently in the two groups, a phenomenon called “convergent evolution.”
“The investigation of sleep and dreaming in the octopus gives us a point of view for the psychological and neurobiological comparison with vertebrates, since the octopus possesses several sophisticated cognitive characteristics that are only seen in some species of vertebrates but with a cerebral architecture very different, ”he said. study co-author Sidarta Ribeiro, founder of the Brain Institute.
Ribeiro noted that previous studies have shown that octopuses, with the most centralized nervous system of all invertebrates, possess exceptional learning abilities, including spatial and social learning, as well as the ability to solve problems.
“Understanding how organisms as different as humans and octopuses can share fundamental traits such as the sleep cycle opens up new avenues for research into animal cognition and for understanding the general principles that shaped the design of the brain in animals. highly intelligent groups of animals, ”Medeiros said.