Octopuses have remarkably similar sleep patterns to humans and may even dream, according to a new study.
Researchers found that, like us, the eight-legged sea creatures transition between two sleep stages – a “quiet” stage and an “active” stage that resembles REM sleep in mammals.
When octopuses sleep, their quiet periods of slumber are punctuated by short bursts of frenzied activity.
Their arms and eyes twitch, their breathing rate quickens, and their skin flashes with vibrant colors – which has led scientists to conjecture that they may even be dreaming.
Researchers from the Okinawa Institute of Science and Technology (OIST) in Japan, along with colleagues from the University of Washington in Seattle, meticulously examined the brain activity and skin patterning in octopuses (Octopus laqueus) during that active period of sleep.
They discovered that they “closely resemble” neural activity and skin patterning behavior seen when awake.
Wake-like activity also occurs during rapid eye movement (REM) sleep in mammals – the phase in which most dreams occur.
The research team said their findings, published in the journal Nature, highlight the remarkable similarities between the sleeping behavior of octopuses and humans.
Senior author Professor Sam Reiter, head of the Computational Neuroethology Unit at OIST, said: “All animals seem to show 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.”
Author Dr. Leenoy Meshulam said: “The fact that two-stage sleep has independently evolved in distantly related creatures, like octopuses, which have large but completely different brain structures from vertebrates, suggests that possessing an active, wake-like stage may be a general feature of complex cognition.”
To begin, the scientists checked whether the octopuses were truly asleep during the active period.
They tested how the mollusks responded to a physical stimulus and found that when in both the quiet and active stage of sleep, the octopuses required stronger stimulation before reacting, compared to when they were awake.
The researchers also discovered that if they prevented the octopuses from sleeping, or disrupted them during the active phase of sleep, the octopuses later entered active sleep sooner and more frequently.
Co-first author Aditi Pophale, a Ph.D. student at OIST, said: “This compensatory behavior nails down the active stage as being an essential stage of sleep that is needed for octopuses to properly function.”
The researchers also delved into the brain activity of the octopuses when awake and asleep.
During quiet sleep, the scientists saw characteristic brain waves that closely resemble certain waveforms seen during non-REM sleep in mammalian brains called sleep spindles.
Although the exact function of the waveforms is unclear even within humans, scientists believe they aid in consolidating memories.
Using a cutting-edge microscope built by co-first author Dr. Tomoyuki Mano, the research team determined that the sleep spindle-like waves occur in regions of the octopuses’ brains associated with learning and memory, suggesting that the waves potentially serve a similar function to humans.
Roughly once an hour, the octopuses entered an active sleep phase for around a minute.
During that stage, the octopuses’ brain activity very closely resembled their brain activity while awake, just like REM sleep does in humans.
The research group also captured and analyzed the changing skin patterns of the octopuses when awake and asleep in ultra-high 8K resolution.
Dr. Meshulam, of the University of Washington, said: “By filming in such high resolution, we can see how each individual pigmented cell behaves in order to create an overall skin pattern. This could help us create simple skin pattern models to understand the general principles of waking and sleeping patterning behavior.”
She explained that when awake, octopuses control thousands of tiny, pigmented cells in their skin, creating a vast array of different skin patterns.
They use the patterns to camouflage themselves in different environments, and in social or threat displays, such as warning off predators and communicating with each other.
During active sleep, the scientists reported that the octopuses cycled through the same skin patterns.
The similarities between active sleep and awake states could be explained by a variety of reasons, according to the research team.
One theory is that octopuses may be practicing their skin patterns to improve their waking camouflage behavior, or simply maintain the pigment cells.
Another idea is that the octopuses could be re-living 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 similar to dreaming.
Prof. Reiter said: “In this sense, while humans can verbally report what kind of dreams they had only once they wake, the octopuses’ skin pattern acts as a visual readout of their brain activity during sleep.”
He added, “We currently don’t know which of these explanations, if any, could be correct.
“We are very interested in investigating further.”
Produced in association with SWNS Talker
Edited by Jessi Rexroad Shull and Kyana Jeanin Rubinfeld
