2023-06-28 17:00:11
When octopuses sleep, their quiet periods of torpor are interrupted by brief bursts of frenetic activity. Her arms and eyes flutter, her breath quickens, and her skin glows with vibrant color.
Now, researchers at Japan’s Okinawa Institute of Science and Technology (OIST), in collaboration with the University of Washington (USA), have taken a closer look at brain activity and the skin pattern of octopuses (Octopus trap) during this active period of sleep and have found that they closely resemble the neural activity and skin pattern seen when awake.
In mammals, wakefulness-like activity also occurs during the sleep phase. rapid eye movements (REM), in which most dreams occur.
There are fascinating similarities between the sleep of octopuses and that of humans
The study, published today in Naturehighlights the remarkable similarities between the behavior during sleep of octopuses and that of humans, and provides fascinating insights into the origin and function of sleep.
“All animals seem to show some form of sleep, even simple animals like jellyfish and fruit flies. But for a long time it was only known that vertebrates cycled between two different phases,” explains lead author, Sam Riderwho heads the OIST Computational Neuroethology Unit.
“The fact that two-stage sleep has evolved independently in distantly related creatureslike octopuses, which have large but completely different brain structures from those of vertebrates, suggests that possessing an active stage, similar to wakefulness, may be a general characteristic of complex cognition“says the author Leenoy Meshulamstatistical physics from the University of Washington.
The scientists checked whether the octopuses were actually asleep during this active period. They tested how they responded to a physical stimulus and discovered that, in both the quiet and active phases of sleep, they needed a stronger stimulus before reactingcompared to when they were awake.
Possessing an active stage, similar to wakefulness, may be a general feature of complex cognition
Leenoy Meshulam, author of the work
The team also found that if they prevented the octopuses from sleeping, or interrupted them during the active phase of sleep, entered the active period earlier and more frequently. “This compensatory behavior confirms that the active phase of sleep is essential for octopuses to function properly,” he says. Aditi Pophaleco-author of the study and PhD student at the OIST.
The researchers also studied the brain activity of the awake and sleeping octopuses. During their peaceful sleep, they observed characteristic brain waves that closely resemble certain forms identified during non-REM sleep in mammalian brains, called sleep spindles.
Although the exact function of these waves is not clear even in humans, experts believe that help consolidate memories. Using a state-of-the-art microscope built by the first co-author Tomoyuki Manothe researchers determined that these sleep spindle-like waves occur in regions of the octopus brain associated with learning and memorysuggesting that they potentially have a function similar to that of humans.
Octopus brain activity during active sleep was similar to that during wakefulness
About once an hour, the octopuses would come into an active sleep phase which lasted about a minute. During this period, the brain activity of the octopuses closely resembled that of when they were awakejust like REM sleep in humans.
The research group also captured and analyzed the changing skin patterns of sleeping and awake octopuses in ultra-high 8K resolution. “By shooting at such a high resolution, we can see how each pigmented cell behaves to create a general skin pattern,” explains Meshulam. “This could help us create simple models to understand the general principles of the behavior of sleep and wake patterns.”
When awake, octopuses control thousands of tiny pigment cells in their skin, creating a wide range of skin patterns. They use them for camouflage in various environments and in social or threat displays, such as warning predators and communicating with each other. During active sleep, the scientists observed that the octopuses repeated these same skin patterns.
The similarities between the active sleep and wake states could be explained by several reasons. One theory is that octopuses may be practicing their skin patterns to enhance their camouflage behavior while awake, or simply by maintaining the pigment cells.
When awake, octopuses control thousands of tiny pigment cells in their skin.
Another intriguing idea is that octopuses could 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 could be doing something like dreaming.
“While humans can only verbally report the type of dreams they have had while awake, the skin pattern of octopuses acts as a a visual reading of your brain activity during sleep,” explains Reiter. “We currently do not know which, if any, of these explanations might be correct. We are very interested in further research,” concludes the professor.
Reference:
Meshulam, L. “Wake-like skin patterning and neural activity during octopus sleep” Nature(2023)
Fuente: SINC
Rights: Creative Commons.
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