Octopuses sleep, just like humans do, but with a peculiar twist. These highly intelligent marine creatures’ snooze sessions feature sudden bursts of vigorous activity.
During their sleep periods, the octopuses’ eyes and arms twitch, their breathing intensifies, and their skin flashes in a stunning display of colors.
A collaborative team from the Okinawa Institute of Science and Technology (OIST) and the University of Washington has recently studied octopuses.
They focused specifically the Octopus laqueus species, monitoring them during these active sleep phases. The team observed intriguing similarities between the octopuses’ brain activity and skin patterns during these sleep episodes and when they are awake.
Our human sleep also comprises such an active phase known as rapid eye movement (REM) sleep. This is when most of our dreams take place.
This intriguing study, published on June 28 in the scientific journal Nature, underscores the striking parallels between human and octopus sleep behaviors. It also offers a unique understanding of the purpose and origins of sleep.
Professor Sam Reiter, the senior author of the study who heads the Computational Neuroethology Unit at OIST, explains.
“All animals seem to show some form of sleep, even simple ones like jellyfish and fruit flies. But for a long time, only vertebrates were known to cycle between two different sleep stages.”
Dr. Leenoy Meshulam, a statistical physicist at the University of Washington, commented further.
“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 prove that the octopuses were indeed asleep during this active stage, the researchers tested their reaction to physical stimuli. The octopuses needed a stronger prod to respond during both the quiet and active stages of sleep. This was compared to when they were awake.
The team also discovered that if they interrupted the octopuses’ sleep or kept them awake, the octopuses would enter the active sleep phase more quickly and frequently.
Aditi Pophale, a co-first author of the study and a PhD student at OIST, stated, “This compensatory behavior nails down the active stage as being an essential stage of sleep that is needed for octopuses to properly function.”
Moreover, the researchers detected characteristic brain waves during the octopuses’ quiet sleep. These closely resemble certain waveforms observed during non-REM sleep in mammalian brains. Scientists know these waveforms as sleep spindles.
Scientists think these waves are crucial in cementing memories while octopuses sleep. A sophisticated microscope used by co-first author Dr. Tomoyuki Mano revealed that these sleep spindle-like waves occur in the parts of the octopuses’ brains tied to learning and memory. This suggests a function similar to humans’.
Approximately once every hour, the octopuses slipped into an active sleep phase lasting around a minute. During this stage, their brain activity closely mirrored their wakeful state. This is much like REM sleep in humans.
The research group also filmed and scrutinized the changing skin patterns of the octopuses during their wakeful and sleep states using ultra-high 8K resolution.
“By filming in such high resolution, we can see how each individual pigmented cell behaves in order to create an overall skin pattern,” said Dr. Meshulam.
“This could help us create simple skin pattern models to understand the general principles of waking and sleeping patterning behavior.”
When awake, octopuses command thousands of pigmented cells in their skin to create numerous different patterns. They use these designs for camouflage, social interactions, and even to warn off predators. During active octopuses’ sleep phases, the scientists noticed the octopuses cycling through the same skin patterns.
The researchers theorize that the similarities between their active sleep and awake states could be due to various reasons. One possibility is that the octopuses are refining their skin patterns to enhance their daytime camouflage. An additional reason could be to simply help maintain their pigment cells.
Another fascinating theory proposes that the octopuses could be revisiting and learning from their waking experiences, such as hunting or evading a predator, by activating the skin pattern associated with each experience. In essence, they could be doing something akin to dreaming.
Prof. Reiter suggests, “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 also expressed an eager interest in future research, stating, “We currently don’t know which of these explanations, if any, could be correct. We are very interested in investigating further.”
Octopuses are a group of highly intelligent marine creatures belonging to the cephalopods family. Here’s what we know about them:
Octopuses usually have a round head (known as a mantle), large eyes, and eight arms (tentacles) covered in suckers. They are bilaterally symmetric.
Their soft bodies allow them to squeeze through tight places, making them excellent escape artists.
They possess three hearts: two that pump blood to the gills and one that pumps it to the rest of the body.
They have blue blood due to the presence of hemocyanin, which contains copper and helps them survive in cold, oxygen-poor water.
Octopuses are solitary creatures and usually mate only once in their lifetime. The male dies shortly after mating, while the female dies soon after her eggs hatch.
People consider them the most intelligent of all invertebrates. Various experiments have demonstrated their problem-solving and short- and long-term memory capabilities.
Observers have seen some octopuses use tools, such as coconut shells and seashells, to hide, communicate, or hunt.
They are able to change color and texture to camouflage with their surroundings. This is used for hunting and also as a defense mechanism.
There are around 300 recognized octopus species. This is over one-third of the total number of known cephalopod species. The giant Pacific octopus is the largest species, while the Octopus wolfi is considered the smallest.
The lifespan of an octopus varies by species. Some may live for as little as six months, while others, like the giant Pacific octopus, can live up to five years under normal circumstances.
Octopuses play a significant role in the food chain. They are predators for various marine animals like crustaceans and other mollusks, and are prey for larger animals, including sharks, whales, and seabirds.
Some species of octopuses live in the open oceans, while others reside along the coasts or on the ocean floor.
When threatened, octopuses release a cloud of black ink that serves as a smokescreen to confuse predators.
They are also known for their jet propulsion escape mechanism. By squeezing water out of their mantles, they can quickly propel themselves away from danger.
Some octopuses, like the blue-ringed octopus, have venom powerful enough to kill humans.
Octopuses have both fascinated and contributed to science. They are studied for their complex nervous systems, behaviors, and camouflaging abilities.
Recently, scientists have been investigating octopus sleep patterns, exploring similarities with human REM sleep.
Keep in mind that this is a broad overview, and each species of octopus may have unique traits and behaviors not mentioned here.