Octopuses sleep study finds they definitely change colors, maybe dream
By Katie Hunt, CNN 3/25/2021
With its eight legs wrapped around itself as if in a hug and its eye pupils narrowed to a slit, the octopus breathes evenly, its body a uniform whitish gray.
Moments later it begins to change color -- a mesmerizing shift between burnt orange and rust red. Its eyes, muscles and sucker pads twitching as if it may be experiencing a particularly vivid dream.
Brazilian scientists say the shifts in color, behavior and movement are evidence of a sleep cycle -- with the octopus switching between active and quiet sleep just as humans switch between deep sleep and REM sleep -- named for the rapid eye movements we experience in this state.
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The findings, published Thursday in the journal iScience, show how sleep may have evolved in a similar way in very different creatures and suggests that octopuses may experience something akin to a dream.
"It is not possible to affirm that octopuses dream because they cannot tell us that, but our results suggest that during 'Active sleep' the octopus experiences a state analogous to REM sleep, which is the state during which humans dream the most," said the study authors Sidarta Ribeiro and Sylvia Medeiros in an email.
Ribeiro is a professor of neuroscience at the Brain Institute of the Federal University of Rio Grande do Norte, and Medeiros is a doctoral student at the same university.
Scientists used to think that only mammals and birds experienced different sleep states -- think of a sleeping cat twitching as though it were chasing a bird in the backyard. More recent research, however, has revealed some reptiles and cuttlefish -- another cephalopod and relative of the octopus -- show non-REM and REM-like sleep.
Octopuses have a very different brain structure to humans, but they share some of the same functions as mammal brains. The creatures have special learning abilities -- including being able to solve problems and other sophisticated cognitive abilities, the authors said.
They said investigating octopus sleep was a "vantage point" for comparing them neurobiologically and psychologically with mammals -- with the sleep similarities likely a consequence of "the very taxing mental loads experienced by these separate groups of animals."
The octopus has long been a source of human fascination. Video footage from 2019 of an octopus called Heidi changing color as she slept in a tank had scientists wondering if the creatures could really dream. The Netflix documentary "My Octopus Teacher" has also showcased the creatures' unique abilities.
Dreaming in GIFs not movies
How were the researchers sure the octopuses they studied were asleep and not just resting? The researchers videoed four members of the Octopus insularis species in their lab and studied the animals' behavior over a period of more than 50 days. The octopuses were very sensitive to very weak stimuli when they were alert, but in both sleep states they needed a strong visual or tactile stimulus to evoke a behavioral response, the scientists said.
Octopuses usually change their skin color for camouflage or for communication but during sleep, environmental factors no longer trigger these patterns. The researchers inferred that the color changes during sleep results from independent brain activity.
The study found that the octopus experiences active sleep after a long episode of quiet sleep. In the case of an octopus, the long period is usually more than six minutes.
"If octopuses indeed dream, it is unlikely that they experience complex symbolic plots like we do. 'Active sleep' in the octopus has a very short duration (typically from a few seconds to one minute)," the authors said via email. "If during this state there is any dreaming going on, it should be more like small videoclips, or even gifs."
VIDEO: THIS VIDEO SHOWS AN OCTOPUS IN QUIET SLEEP AND ACTIVE SLEEP. view more
CREDIT: SYLVIA S L MADEIROS
Octopuses have two alternating sleep states, study shows
Octopuses are known to sleep and to change color while they do it. Now, a study publishing March 25 in the journal iScience finds that these color changes are characteristic of two major alternating sleep states: an "active sleep" stage and a "quiet sleep" stage. The researchers say that the findings have implications for the evolution of sleep and might indicate that it's possible for octopuses to experience something akin to dreams.
Scientists used to think that only mammals and birds had two sleep states. More recently, it was shown that some reptiles also show non-REM and REM sleep. A REM-like sleep state was reported also in cuttlefish, a cephalopod relative of the octopus.
"That led us to wonder whether we might see evidence of two sleep states in octopuses, too," says senior author Sidarta Ribeiro of the Brain Institute of the Federal University of Rio Grande do Norte, Brazil. "Octopuses have the most centralized nervous system of any invertebrate and are known to have a high learning capacity."
To find out, the researchers captured video recordings of octopuses in the lab. They found that during 'quiet sleep' the animals were still and quiet, with pale skin and eye pupils contracted to a slit. During 'active sleep,' it was a different story. The animals dynamically changed their skin color and texture. They also moved their eyes while contracting their suckers and body with muscular twitches.
"What makes it more interesting is that this 'active sleep' mostly occurs after a long 'quiet sleep'--generally longer than 6 minutes--and that it has a characteristic periodicity," Ribeiro says.
The cycle would repeat at about 30- to 40-minute intervals. To establish that these states indeed represented sleep, the researchers measured the octopuses' arousal threshold using visual and tactile stimulation tests. The results of those tests showed that in both 'active' and 'quiet sleep' states, the octopuses needed a strong stimulus to evoke a behavioral response in comparison with the alert state. In other words, they were sleeping.
The findings have interesting implications for octopuses and for the evolution of sleep. They also raise intriguing new questions.
"The alternation of sleep states observed in the Octopus insularis seems quite similar to ours, despite the enormous evolutionary distance between cephalopods and vertebrates, with an early divergence of lineages around 500 million years ago," says first author and graduate student Sylvia Medeiros of the Brain Institute of the Federal University of Rio Grande do Norte, Brazil.
"If in fact two different sleep states evolved twice independently in vertebrates and invertebrates, what are the essential evolutionary pressures shaping this physiological process?" she asks. "The independent evolution in cephalopods of an 'active sleep' analogous to vertebrate REM sleep may reflect an emerging property common to centralized nervous systems that reach a certain complexity."
Medeiros also says that the findings raise the possibility that octopuses experience something similar to dreaming. "It is not possible to affirm that they are dreaming because they cannot tell us that, but our results suggest that during 'active sleep' the octopus might experience a state analogous to REM sleep, which is the state during which humans dream the most," she says. "If octopuses indeed dream, it is unlikely that they experience complex symbolic plots like we do. 'Active sleep' in the octopus has a very short duration--typically from a few seconds to one minute. If during this state there is any dreaming going on, it should be more like small videoclips, or even gifs."
In future studies, the researchers would like to record neural data from cephalopods to better understand what happens when they sleep. They're also curious about the role of sleep in the animals' metabolisms, thinking, and learning.
"It is tempting to speculate that, just like in humans, dreaming in the octopus may help to adapt to environmental challenges and promote learning," Ribeiro says. "Do octopuses have nightmares? Could octopuses' dreams be inscribed on their dynamic skin patterns? Could we learn to read their dreams by quantifying these changes?"
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This work was supported by the State University of Rio Grande do Norte (UERN), the Coordenação de Aperfeicoamento de Pessoal de Nível Superior (CAPES), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and from the São Paulo Research Foundation (FAPESP) Center for Neuromathematics.
iScience, Medeiros et al.: "Cyclic alternation of quiet and active sleep states in the octopus" https://www.cell.com/iscience/fulltext/S2589-0042(21)00191-7
iScience (@iScience_CP) is an open access journal from Cell Press that provides a platform for original research and interdisciplinary thinking in the life, physical, and earth sciences. The primary criterion for publication in iScience is a significant contribution to a relevant field combined with robust results and underlying methodology. Visit http://www.
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