The octopus is an extraordinary creature – and not just because of its eight limbs, three hearts, blue blood, squirting ink, camouflage ability, and the tragic fact that it dies after mating.
A study by researchers in Brazil published Thursday shows that this animal, already considered arguably the smartest invertebrate, experiences two major alternating sleeping states that are eerily similar to humans – and could even dream.
The findings, the researchers said, provide new evidence that the octopus possesses a complex and advanced neurobiology that underlies an equally sophisticated behavioral repertoire, while also providing a broader understanding of the evolution of sleep, a crucial biological function.
Octopuses were previously known to experience sleep and change color while dormant. In the new study, the researchers observed a species called Octopus insularis in a lab setting. They found that these color changes are related to two different sleep states: ‘restful sleep’ and ‘active sleep’.
During “silent sleep” the octopus remains still, with pale skin and pupils of the eyes contracted into a split. During “active sleep” it dynamically changes its skin color and texture and moves both eyes as it contracts its suction cups and body, twitching.
A repeating cycle was observed during sleep. “Silent sleep” usually lasted about seven minutes. The subsequent “active sleep” usually lasted less than a minute.
This cycle appears analogous, the researchers said, to the alternating “rapid eye movement” or REM and “non-rapid eye movement” or non-REM sleep states experienced by humans as well as other mammals, birds and reptiles. .
Vivid dreaming occurs during REM sleep because a person’s eyes move quickly, breathing becomes irregular, the heart rate increases, and the muscles become paralyzed not to carry out the dreams. Non-REM sleep offers more deep sleep and fewer dreams.
Lead author Sylvia Medeiros said the findings suggest octopuses experience dreams or something similar.
“If octopuses do indeed dream, they are unlikely to experience complex symbolic plots like us,” said Medeiros, a neuroscience doctoral student at the Brain Institute at the Federal University of Rio Grande do Norte.
“Active sleep” in the octopus has a very short duration, usually from a few seconds to a minute. If dreaming occurs during this state, it should look more like small video clips, or even GIFs, ”added Medeiros.
Scientists are looking for a better understanding of the origin and evolution of sleep.
Since the last common ancestor of vertebrates, including humans, and cephalopods, including octopuses, lived more than half a billion years ago, it seems unlikely that their similar sleeping patterns were established before their evolutionary divergence, the researchers said.
That would mean, they added, that this similar sleep pattern arose independently in the two groups, a phenomenon called “convergent evolution.”
“The study of sleep and dreaming in the octopus gives us a vantage point for the psychological and neurobiological comparison with vertebrates, as the octopus has several advanced cognitive features seen only in some vertebrates, but with very different brain architecture,” 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 problem-solving abilities.
Understanding how such different organisms as humans and octopuses can share fundamental traits, such as the sleep cycle, opens new avenues for the investigation of animal cognition and for understanding the general principles that shaped the brain in these highly intelligent groups. animals, ”’said Medeiros.