Octopus may experience REM sleep, and dream, much like we do
Scientists have spent years trying to work out if octopuses, whose brains have some remarkable similarities to our own, have dreams. A recent study even purported that the eight-armed cephalopods can have physical reactions in their sleep, akin to being attacked by a predator, suggesting they experience nightmares.
Now, researchers from the Okinawa Institute of Science and Technology (OIST), in collaboration with the University of Washington (UW), have examined the brain activity and patterning behavior of a small, shallow-water octopus from Japan, Octopus laqueus, and confirmed that not only is the animal asleep during these ‘active sleep’ moments, but it shares similarities to our own rapid eye movement (REM) slumber.
When octopuses snooze, their ‘quiet sleep’ is interrupted with short periods of frenzied REM-adjacent behavior in ‘active sleep’ – their patterning flashes brightly, their eyes and arms twitch and their breathing rate quickens.
While the researchers can’t claim to have proved the animals are dreaming, the REM state in mammals is the stage of sleep in which dreams most frequently occur.
“All animals seem to show some form of sleep, even simple animals like jellyfish and fruit flies,” said Sam Reiter, senior author of the study and professor at OIST. “But for a long time, only vertebrates were known to cycle between two different sleep stages.”
During ‘quiet sleep,' the octopus brain emitted the kind of waveforms seen during non-REM sleep in mammals like us, known as sleep spindles, which are thought to be related to consolidating memories. With a microscope built by the study’s first author, Tomoyuki Mano, these sleep-spindle-like waves were found to be originating in the brain region associated with learning and memory, hinting that they could function much like they do in humans.
“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,” said Leenoy Meshulam from UW.
And when scientists aren’t giving octopuses ecstasy, they’re “gently brushing their skin with a paintbrush.” This interruption every two to three minutes over a period of 48 hours was to see what effect sleep deprivation would have on those two sleep states. It resulted in a greater rate of active sleep, which was initiated more rapidly, revealing that with absolute certainty this state of flashing and twitching was indeed sleep.
“This compensatory behavior nails down the active stage as being an essential stage of sleep that is needed for octopuses to properly function,” said Aditi Pophale, co-first author of the study and PhD student at OIST.
Furthermore, high-definition filming of the octopus patterning while in active sleep showed that the animals cycled through the same colors and shapes as when awake. While it’s also likely the octopus does this for ‘practice’ in camouflage for when it’s awake, or to simply maintain the health of the pigment cells, it could also indicate the animal is remembering or re-learning moments of its conscious periods – like a dream state.
“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,” said Reiter. “We currently don’t know which of these explanations, if any, could be correct. We are very interested in investigating further.”
Meanwhile, also out of OIST, along with the Max Planck Institute for Brain Research, scientists have discovered more about the octopus’ cousins, the cuttlefish, and how their ability to color-correct their camouflaging patterns indicates a much greater level of cognitive function and autonomy over their changes than previously thought.
Cuttlefish are masters at blending into their environment by use of their skin organs, chromatophores, which contract and relax as directed by neurons in the brain to adjust pigmentation.
But as Sam Reiter, who also worked on the octopus study, found out, the devil is in the detail.
“Prior research suggested that cuttlefish only had a limited selection of pattern components that they would use to achieve the best match against the environment,” Reiter said. “But our latest research has shown that their camouflaging response is much more complicated and flexible – we just hadn’t been able to detect it as previous approaches were not as detailed or quantitative.”
Using ultra-high-resolution cameras to closely examine the skin of the European cuttlefish (Sepia officinalis) against rapidly cycling backgrounds, they collected around 200,000 images that were analyzed by a type of AI.
The fascinating results showed that the animal would cycle through patterns, adjusting it with each individual chromatophore, of which they potentially have millions of, until they settled on an overall look they approved of.
The scientists observed them ‘color-correcting,’ and each path to the final pattern was different, even when exposed to the same background, suggesting a complexity in their behavior that hasn’t been observed until now.
“The cuttlefish would often overshoot their target skin pattern, pause, and then come back,” said Theodosia Woo, joint first author of the study from the Max Planck Institute for Brain Research. “In other words, cuttlefish don’t simply detect the background and go straight to a set pattern, instead, it is likely that they continuously receive feedback about their skin pattern and use it to adjust their camouflage.
“Exactly how they receive that feedback – whether they use their eyes, or whether they have a sense of how contracted the muscles around each chromatophore are – we don’t yet know,” she added.
“The next step is to capture neural recordings from cuttlefish brains, so we can further understand exactly how they control their unique and fascinating skin patterning abilities,” said Xitong Liang, joint first author of the study and formerly at the Max Planck Institute.
Check out the videos below to see the octopus changing patterns in its REM-like active sleep state, and below it, the cuttlefish's incredible color-correcting skills as it searches for just the right look.