In a video that went viral this week, an octopus named Heidi sleeps with her tentacles suctioned to the glass walls of an aquarium in the living room of David Scheel, a marine biologist at Alaska Pacific University. The camera captures her skin as it morphs from smooth and stony to a crusty-looking yellow. Then it flashes maroon for a second before settling back to white.
Scheel narrates the scene, conjecturing that Heidi is hunting for crab in her mind’s eye. “If she’s dreaming, this is a dramatic moment,” he says in the video.
The clip, part of a PBS Nature special that aired October 2, quickly took off on social media. But while Scheel and the online community delighted at the idea of a dreaming Heidi, experts challenge the idea that octopuses like her can “dream” in the way humans understand it.
“Almost no animal is proven to have dreams because you can’t verbalize and talk to them and get the feedback,” says Roger Hanlon, a senior scientist at the Marine Biological Laboratory. “There’s no science behind it, especially for an animal with a different body form, like an octopus.”
As Elizabeth Preston at New York Times reports, octopuses and other cephalopods are highly intelligent. Cephalopods, however, are invertebrates, meaning their family tree diverged from ours before the development of the backbone. That split means octopus brains and human brains developed big differences. Unlike humans, whose behavior is controlled by a central nervous system, octopuses have a distributed nervous system. Of their 500 million neurons, 350 million exist in the arms, meaning octopus arms can make decisions without any input from the brain.
“Color change is just a neuromuscular behavior, just like moving our arms or fingers or anything else,” Stanford biologist William Gilly tells Jess Romeo at Popular Science. “It’s not necessarily a conscious thing.”
Octopuses’ can quickly and drastically change colors thanks to chromatophores, which are elastic cells of pigment that contract and expand to make certain colors more visible. Color and textural shifts in the octopus’ skin are mostly controlled by the brain, but may also be subconscious.
Though scientists have long observed how octopuses change between different skin textures and colors when the animals are awake, octopuses often seclude themselves under rocks or in dens to protect against predators while they sleep. This may be why the footage of Heidi openly displaying her transformations is so remarkable.
Experts don’t yet fully know what happens to octopuses while resting, but they have gotten closer to understanding how they sleep. In a study published this year, researchers found that cuttlefish—close relatives to the octopus—display REM-like sleeping patterns. While in this state, the cuttlefish flashed portions of typical daytime chromatophore patterning, and each expressed patterns with different intensity.
“They’re out and doing things all day long, then they go into this quiet period of REM-like sleep,” says Hanlon, who co-authored the paper. “My guess is that they’re consolidating long-term memory.”
To test whether octopuses similarly experience REM-like cycles akin to humans, scientists will likely need to implant electrodes into their brains—a task that can be challenging due to the octopuses’ cunning ability to remove unwanted object from themselves with their tentacles.
And to explain what happens to creatures like Heidi when they fall asleep, researchers must define their terminology thoughtfully, so as not to compare the very human experience of dreaming to one that may be totally different in an octopus.
“It’s a question of interpretation at this point,” says Michael Vecchione, a NOAA cephalopod biologist at the Smithsonian Institution’s National Museum of Natural History. “We have to be careful about inserting our own perspective on things when we’re interpreting other animals’ behavior.”
It’s far too soon to know if octopuses can actually dream—or even sleep—like us. But even if we don’t yet know what happens to Heidi when she shuts her eyes, scientists hope videos like this will inspire others to more closely study cephalopods’ sleeping and cognitive functions.