Researchers have discovered that octopuses show two unique sleep stages: a quiet stage and an active one that resembles REM sleep in mammals. Throughout the active sleep stage, octopuses display habits and neural activity comparable to their awake state, which may serve a function comparable to dreaming in human beings.
Like humans, octopuses transition between two sleep stages– a quiet stage and an active phase that resembles REM sleep in mammals. However could this suggest that octopuses dream?
When octopuses sleep, their quiet durations of sleep are stressed by short bursts of crazy activity. Their arms and eyes jerk, their breathing rate quickens, and their skin flashes with lively colors.
Now, researchers from the Okinawa Institute of Science and Technology (OIST), in collaboration with the University of Washington, have closely analyzed the brain activity and skin patterning in octopuses (Octopus laqueus) throughout this active duration of sleep and discovered that they carefully look like neural activity and skin patterning behavior seen when awake. Wake-like activity likewise occurs during rapid-eye-movement sleep (REM) sleep in mammals– the stage in which most dreams take place.
This quiet sleep is stressed by bursts of sleep that show wake-like activity (active sleep) approximately every hour. They evaluated how the octopuses responded to a physical stimulus and discovered that when in both the active and peaceful phase of sleep, the octopuses required more powerful stimulation before responding, compared to when they were awake. The group likewise found that if they avoided the octopuses from sleeping, or disrupted them throughout the active stage of sleep, the octopuses later went into active sleep faster and more regularly.
Throughout quiet sleep, the scientists saw particular brain waves that closely resemble specific waveforms seen during non-REM sleep in mammalian brains called sleep spindles. During active sleep, the researchers reported that the octopuses cycled through these same skin patterns.
By Okinawa Institute of Science and Innovation (OIST) Graduate University
June 30, 2023
During quiet sleep, octopus laqueus appears white and motionless. This peaceful sleep is stressed by bursts of sleep that show wake-like activity (active sleep) approximately every hour. Credit: Keishu Asada (OIST).
The study, published on June 28 in the journal Nature, highlights the exceptional similarities between the sleeping habits of octopuses and people and provides fascinating insights about the origin and function of sleep.
” All animals seem to show some form of sleep, even basic animals like jellyfish and fruit flies. But for a long period of time, only vertebrates were understood to cycle in between 2 different sleep phases,” said senior author, Professor Sam Reiter, who leads the Computational Neuroethology Unit at OIST.
These new discoveries into how octopuses sleep came through a check out to OIST by Dr. Leenoy Meshulam, a statistical physicist at the University of Washington, who spent 3 months as a guest of the OIST Theoretical Sciences Visiting Program.
” The fact that two-stage sleep has independently developed in distantly related animals, like octopuses, which have totally various however large brain structures from vertebrates, recommends that possessing an active, wake-like stage might be a general feature of intricate cognition,” stated Dr. Meshulam.
An octopus from the species Octopus laqueus alters its skin patterns during active sleep. Credit: OIST.
To begin, the scientists examined whether the octopuses were genuinely asleep throughout this active duration. They checked how the octopuses reacted to a physical stimulus and discovered that when in both the quiet and active phase of sleep, the octopuses needed more powerful stimulation before responding, compared to when they were awake. The team also discovered that if they avoided the octopuses from sleeping, or interrupted them throughout the active phase of sleep, the octopuses later entered active sleep earlier and more frequently.
” This countervailing habits nails down the active phase as being an important stage of sleep that is needed for octopuses to effectively function,” stated Aditi Pophale, co-first author of the research study and PhD student at OIST.
When awake and asleep, the researchers likewise dove into the brain activity of the octopuses. During peaceful sleep, the scientists saw particular brain waves that carefully look like particular waveforms seen during non-REM sleep in mammalian brains called sleep spindles. Although the precise function of these waveforms is unclear even within humans, scientists think they aid in consolidating memories. Utilizing an innovative microscopic lense developed by co-first author Dr. Tomoyuki Mano, the scientists identified that these sleep spindle-like waves occur in regions of the octopuses brains related to knowing and memory, recommending that these waves possibly serve a similar function to people.
Roughly once an hour, the octopuses entered an active sleep stage for around a minute. Throughout this phase, the octopuses brain activity really carefully resembled their brain activity while awake, similar to REM sleep carries out in humans.
The research group also recorded and examined the altering skin patterns of the octopuses when awake and asleep in ultra-high 8K resolution.
” By filming in such high resolution, we can see how each specific pigmented cell behaves in order to produce a total skin pattern,” said Dr. Meshulam. “This might help us produce basic skin pattern designs to understand the basic principles of waking and sleeping pattern habits.”.
When awake, octopuses manage countless small, pigmented cells in their skin, developing a vast selection of different skin patterns. They use these patterns to camouflage themselves in different environments, and in social or risk display screens, such as cautioning off predators and interacting with each other. During active sleep, the researchers reported that the octopuses cycled through these same skin patterns.
The similarities in between active sleep and awake states could be discussed by a variety of factors, said the researchers. One theory is that octopuses might be practicing their skin patterns to improve their waking camouflage habits, or merely preserving the pigment cells.
Another intriguing idea is that the octopuses could be re-living and gaining from their waking experiences, such as hunting or hiding from a predator, and reactivating the skin pattern related to each experience. In other words, they could be doing something comparable to dreaming.
” In this sense, while people can verbally report what kind of dreams they had just as soon as they wake, the octopuses skin pattern functions as a visual readout of their brain activity throughout sleep,” said Prof. Reiter.
He included, “We presently do not know which of these descriptions, if any, might be right. We are really interested in investigating further.”.
Reference: “Wake-like skin pattern and neural activity throughout octopus sleep” by Aditi Pophale, Kazumichi Shimizu, Tomoyuki Mano, Teresa L. Iglesias, Kerry Martin, Makoto Hiroi, Keishu Asada, Paulette García Andaluz, Thi Thu Van Dinh, Leenoy Meshulam and Sam Reiter, 28 June 2023, Nature.DOI: 10.1038/ s41586-023-06203-4.