Heidi the octopus is sleeping. Her body is still, eight arms tucked neatly away. But her skin is restless. She turns from ghostly white to yellow, flashes deep red, then goes mottled green and bumpy like plant life. Her muscles clench and relax, sending a tendril of arm loose.
From the outside, the cephalopod looks like a person twitching and muttering during a dream, or like a napping dog chasing dream-squirrels.
“If she is dreaming, this is a dramatic moment,” David Scheel, an octopus researcher at Alaska Pacific University, said in the documentary. Heidi was living in a tank in his living room when her snooze was captured by the film crew, and he speculates that she is imagining catching and eating a crab.
But an octopus is almost nothing like a person. So how much can anyone really say with accuracy about what Heidi was doing?
When our two branches of the animal family tree diverged, backbones hadn’t been invented. Yet octopuses, cuttlefish and squid, on their own evolutionary path, developed impressive intelligence. They came up with their own way to build big brains. Much of an octopus’s brain is spread throughout its body, especially its arms. It makes sense to be cautious when we guess what’s going on in these animals’ minds.
Looking at a behavior like Heidi’s is “a bit like going to a crime scene,” said Nicola Clayton, a psychologist at the University of Cambridge who studies comparative cognition.
“You’ve got some evidence in front of you, but you’d need to know so much more to understand better what’s causing the behavior.”
It’s only conjecture to say the octopus is dreaming without more data, she said. Does the sequence of Heidi’s color changes match an experience she had while awake? Dreaming in humans mostly happens during rapid-eye movement, or R.E.M., sleep. Could we observe something similar in octopuses? Dr. Clayton points out that a human sleeper might flush red because she’s overheated.
Alex Schnell, a cephalopod intelligence researcher in Dr. Clayton’s lab, said some of her colleagues aren’t always careful about interpreting behaviors they’ve observed. Simpler explanations are more likely than complex ones. Dr. Scheel himself acknowledged that Heidi’s nighttime transformations could be nothing more than the twitching of muscles that control her color-changing organs.
Daniel Margoliash, a neuroethologist at the University of Chicago, said the video of Heidi is “spectacular.” Research by Dr. Margoliash and others has shown that many birds go through sleep stages including R.E.M., like humans and other mammals do, rather than just turning off at night like a light switch. He has also discovered that activity patterns in the brains of sleeping songbirds match patterns that appear during the day while they’re singing.
Scientists can’t ask a songbird whether it sees anything while it sleeps. “But it’s as if the birds are dreaming of singing,” he said.
Evidence suggests that sleep stages, and perhaps dreaming, evolved multiple times in vertebrates, Dr. Margoliash said. Why not in the squishy cephalopods too?
He says big, complicated nervous systems create certain problems for their owners, no matter what those brains look like. The brains need to be calmed and regulated; experiences and memories need to be consolidated. Maybe similar sleep patterns evolved across the animal kingdom to solve those problems, Dr. Margoliash said. “If that’s true, then I expect that dreaming in fact exists in many animals.”
Recent studies have shown that cuttlefish cycle in and out of an R.E.M.-like state while they’re sleeping. Their eyes move quickly, and changing color patterns flash across their skin. In the video of Heidi, Dr. Margoliash said that to him, “it looked like there was a period of time when the eyes were clearly moving,” as in R.E.M. sleep.
“Who knows! But you can’t ignore it,” he added. “You have to study it.”