Summary: Octopuses, despite their completely different brain structures, show sleep cycles similar to humans.
Research shows octopuses enter an active sleep stage similar to REM sleep in humans, suggesting the presence of this sleep stage in complex cognition in the species. The scientists also discovered that sleep disruption prompts octopuses to re-enter this active phase more often, underscoring its need.
Finally, changes in the skin patterns of octopuses during this active sleep phase suggest that they can ‘dream’ in their own unique way.
- Octopuses exhibit an active stage of sleep that resembles REM sleep in mammals, suggesting that this stage of sleep evolved independently in creatures with complex cognition.
- Disruption of sleep causes octopuses to enter this active sleep stage more often, demonstrating its importance.
- During this active sleep phase, changing skin patterns of octopuses indicate that they may be ‘dreaming’ or rehearsing their waking experiences.
When octopuses sleep, their quiet periods of slumber are punctuated by short bursts of exciting activity. Their arms and eyes twitch, their breathing quickens, and their skin flashes vibrant colors.
Now, researchers from the Okinawa Institute of Science and Technology (OIST), in collaboration with the University of Washington, have closely observed brain activity and skin patterns in octopuses (Octopus trap) during this active period of sleep and discovered that they closely resemble the neural activity and skin pattern behavior seen when awake. Wake-like activity also occurs during rapid eye movement (REM) sleep in mammals – the stage in which most dreams occur.
The study, published on 28 June in Naturehighlights striking similarities between the sleep behavior of octopuses and humans and provides fascinating insights into the origins and function of sleep.
“All animals seem to exhibit some form of sleep, even simple animals like jellyfish and fruit flies. But for a long time, only vertebrates were known to cycle between two different sleep stages ,” said senior author, Professor Sam Reiter, who heads the Computational Neuroethology Unit at OIST.
“The fact that the two stages of sleep have evolved independently in distantly related creatures, such as octopuses, which have large but completely different brain structures from vertebrates, indicates that the existence of an active, wake-like stage may be a general feature of complex cognition,” said author Dr. Leenoy Meshulam, a statistical physicist at the University of Washington, who helped design the research during her three-month stay at OIST as a guest of the Theoretical Sciences Visiting Program.
To begin, the scientists examined whether the octopuses actually sleep during this active period. They tested how the octopuses responded to a physical stimulus and found that when in both the quiet and active stages of sleep, the octopuses needed stronger stimulation before responding, compared to when they were awake.
The team also found that if they prevented the octopuses from sleeping, or interrupted the active sleep phase, the octopuses entered active sleep earlier and more often.
“This compensatory behavior nails the active phase as an important phase of sleep that is necessary for octopuses to function properly,” said Aditi Pophale, co-first author of the study and PhD student at OIST.
The researchers also studied the brain activity of the octopuses when they were awake and asleep. During quiet sleep, scientists have observed brain wave characteristics that closely resemble certain waveforms seen in non-REM sleep in mammalian brains called sleep spindles.
Although the exact function of these waveforms is unclear even within humans, scientists believe they help consolidate memories. Using a cutting-edge microscope developed by co-first author Dr. Tomoyuki Mano, the researchers determined that these sleep spindle-like waves occur in the brain regions of octopuses associated with learning and memory, suggesting that these waves potentially serve a similar function. to people.
About once an hour, octopuses enter the active sleep phase for about a minute. During this stage, the brain activity of octopuses very closely resembles their brain activity while awake, such as REM sleep in humans.
The research team also captured and analyzed the octopuses’ changing skin patterns when awake and asleep in ultra-high 8K resolution.
“By filming at such high resolution, we can see how each individual pigmented cell acts to create the overall pattern of the skin,” said Dr. Meshulam. “This can help us create simple models of skin patterns to understand the general principles of waking and sleeping behavior.”
When awake, octopuses control thousands of tiny, pigmented cells in their skin, creating a wide range of different skin patterns. They use these patterns to camouflage themselves in different environments, and in social or threat displays, such as warning predators and communicating with each other. During active sleep, scientists report that octopuses rotate in the same skin patterns.
The similarities between active sleep and the awake state can be explained by various factors, scientists say. One theory is that octopuses may be training their skin patterns to improve their waking behavior of camouflage, or simply maintaining pigment cells.
Another intriguing idea is that octopuses may be reliving and learning from their waking experiences, such as hunting or hiding from a predator, and reactivating the skin pattern associated with each experience. In other words, they may be doing something similar to dreaming.
“In this sense, while humans can verbally report what kind of dreams they had only the moment they wake up, the skin pattern of octopuses serves as a visual readout of their brain activity during sleep, ” said Prof. Reiter.
He added, “We currently do not know which of these explanations, if any, may be correct. We are interested in investigating further.”
About this neuroscience research news
Author: Tomomi Okubo
Please contact: Tomomi Okubo – OIST
Image: Image credited to Neuroscience News
Original Research: Open access.
“Wake-like skin patterning and neural activity during octopus sleep” by Sam Reiter et al. Nature
Wake-like skin patterning and neural activity during octopus sleep
During sleep, many vertebrate groups alternate between at least two stages of sleep: rapid eye movement and slow wave sleep, which is partly characterized by wake-like and synchronous brain activity, respectively.
Here we delineate the neural and behavioral correlates of two sleep stages in octopuses, marine invertebrates that evolutionary diverged from vertebrates approximately 550 million years ago and independently evolved large brains and cognitive sophistication. – behavior. ‘Quiet’ sleep in octopuses is rhythmically interrupted by approximately 60-s bouts of pronounced body movements and rapid changes in skin pattern and texture.
We show that these bouts are homeostatically regulated, rapidly reversible and have a higher arousal threshold, representing a distinct ‘active’ stage of sleep.
Computational analysis of active sleep skin patterning reveals diverse dynamics through a set of patterns that are maintained in octopuses and strongly resemble those seen while awake.
High-density electrophysiological recordings from the midbrain show that local field potential (LFP) activity during active sleep resembles wakefulness. LFP activity differs among brain regions, with the strongest activity during active sleep found in the superior frontal and vertical lobes, anatomically connected regions associated with learning and memory function.
During quiet sleep, these regions are relatively silent but generate LFP oscillations that resemble mammalian sleep spindles in frequency and duration.
The range of similarities among vertebrates suggests that aspects of the two stages of sleep in octopuses may represent interrelated features of complex cognition.
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