When humans sleep, we enter two phases: rapid eye movement (REM) sleep, in which our brains are active similarly to how they are when we’re awake, and non-REM sleep, which is very deep. Other vertebrates follow this pattern, but a new study finds a certain eight-armed invertebrate may, too.
Research recently published in the journal Nature examined the sleep of octopuses, which the researchers say have evolved large brains and behavioral sophistication. The study found that these clever animals also have a two-phase sleep pattern, with one involving wakefulness. The findings indicate that their bigger brains could have something to do with this.
Dr. Leenoy Meshulam, study co-author and statistical physicist at the University of Washington, says, “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 conduct their research, the team measured the brain activity of octopuses while they were awake and asleep. During the quieter portion of the animals’ sleep, their brain waves were similar to those of mammals during non-REM sleep.
On the other hand, their more wakeful state was associated with brain waves like those humans demonstrate during REM sleep, which mirrors those of our waking hours. The octopuses are a little more interesting during this stage than we are, though. Their skin was observed rotating through changing patterns they use when awake for safety, or to communicate with each other.
The scientists say this camouflage behavior could be due to a few reasons: the octopus could be practicing their skin changes to be better at it when awake, maintaining their pigment cells, or re-living and learning from waking experiences involving skin changes. That last theory would mean they were doing something similar to dreaming.
Sam Reiter, senior author who leads the Computational Neuroethology Unit at Okinawa Institute of Science and Technology, explains, “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.”
This isn’t the only study that demonstrates the octopus’ powerful brain. Other research has found that the animal can solve mazes, get in and out of containers, and recognize people.