Octopuses are not only wonderfully strange, but they are also intellectually fascinating. These boneless, shape-morphing, and color-changing creatures have fascinating features such as three hearts, pulsating veins, ink sacs to ward off predators, and an elaborate brain.
Researchers recently found yet another exciting thing about octopuses — they sleep, and maybe even dream, just like humans. Scientists from the Okinawa Institute of Science and Technology (OIST) in Japan found that they have two sleep stages: a “quiet” phase that transitions to an “active” phase that resembles REM sleep in humans.
When sleeping, their calm phases were interrupted by short periods of intense activity. Their tentacles and eyes twitch, their breathing intensifies, and their skin flashes with different vivid colors, leading scientists to theorize that they might be dreaming.
Fascinating octopus and animal sleep similarities
In this collaborative study, researchers from OIST in Japan and the University of Washington, U.S., studied the Octopus laqueus species meticulously, noting their brain activity and skin patterning during the quiet and active sleep phases.
About once every hour, the octopuses entered an active sleep phase for about a minute. The team noted stunning similarities between their neural activity during this sleep period and when they were awake.
Professor Sam Reiter, the head of the Computational Neuroethology Unit at OIST and the study’s lead author, 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.” (earth.com)
Another team member, Dr. Leenoy Meshulam, added: “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.” (earth.com)
How did they know the octopuses were asleep?
To determine if the octopuses were indeed asleep, the team conducted several experiments to test how they responded to physical stimuli. They discovered that during both the calm and active phases of sleep, they needed stronger stimulation before reacting or “waking” than when they were awake.
Also, when disturbed during their active phases of sleeping, they later entered the active phase sooner. In short, they fell asleep faster.
“This compensatory behavior nails down the active stage as being an essential stage of sleep that is needed for octopuses to properly function,” said co-first author Aditi Pophale, a doctoral student at OIST. (earth.com)
Octopuses’ changing neural activity during sleep
During non-REM (NREM) sleep or “quiet sleep,” mammalian brains have distinct brain waveforms called sleep spindles. Interestingly, the team found octopuses’ brain waves during “quiet” sleep that resemble certain waveforms in human non-REM sleep spindles.
Using an advanced microscope developed by team member Dr. Tomoyuki Mano, they could see that these spindle-like waves occur in specific parts of octopuses’ brains associated with memory and learning. Even in humans, the exact purpose of these waveforms is undetermined, but scientists speculated that they have memory-related functions in octopuses like in humans.
When awake, octopuses display vivid colors by controlling thousands of tiny pigmented cells on their skin. They use these patterns to camouflage, ward off predators, or, in social contexts, communicate with each other. As mentioned, during their active sleep, they found that the octopuses underwent the same skin-changing patterns.
Why do octopuses’ brain activities and skin patterns change during active sleep?
The human-octopus evolutionary tree is said to have branched about 500 million years ago, but it seems sleeping, and maybe dreaming, is as vital to them as it is to humans.
One theory is that they are practicing their skin patterns to improve their waking camouflage behavior. Or perhaps to maintain their skin pigmentation.
Another fascinating theory is that, akin to humans, octopuses are reliving and learning from their daytime activities, such as hunting or evading predators. They may be reactivating the skin patterns linked with each experience; an action similar to dreaming.
“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. We currently don’t know which of these explanations, if any, could be correct. We are very interested in investigating further,” says Prof. Reiter. (earth.com)
While sleeping, animals have to suspend all the other prime activities. They can’t defend themselves against predators, hunt or forage for food, find a mate, or even protect their young ones. Scientists may not know the exact purposes of octopuses’ sleep patterns, but it’s easy to infer that sleep is one of the most critical needs for life.
