Octopuses May Have Vivid Nightmares, Video Suggests

Costello the octopus had a rough life. While living off the coast of the Florida Keys, he got into a fight with another sea creature, losing the majority of two arms and suffering damage to a third arm from the unknown predator.

That traumatic incident apparently stuck with Costello, a male Brazilian reef octopus—so much so, that he may even have had nightmares about it later in life. That’s the theory posed by researchers in a paper published last week on the preprint server bioRxiv. In the study, which has not yet been peer-reviewed, the team describes Costello’s bizarre behaviors while sleeping, which suggest octopuses can have vivid dreams.

After the cephalopod’s unfortunate run-in in the wild, a vendor caught and sold him to researchers in New York in early 2021. Though Costello died naturally less than two months later from an intestinal parasite, his short-lived stint in captivity may someday help scientists unravel the mysteries surrounding octopus neurology and evolution.

The curious observations began when Eric Ramos, a neuroscientist at The Rockefeller University, entered the lab one morning and discovered that the water in Costello’s tank was murky and filled with ink, reports New Scientist’s Michael Le Page. Ramos was immediately intrigued, since expelling ink is typically a defense mechanism that cephalopods use to ward off predators—but Costello only shared his tank with tiny, non-predatory fish.

To look for some explanation, Ramos checked the tapes from cameras pointed at Costello’s tank 24/7.

What he saw in the footage surprised him. At first, Costello was sleeping peacefully. But suddenly—and without apparent provocation—the animal began frantically moving. His skin color changed, he spun around, he extended his mantle and he inked—all behaviors linked with fending off predators.

“It was really bizarre, because it looked like he was in pain; it looked like he might have been suffering, for a moment,” Ramos tells Live Science’s Ethan Freedman. “And then he just got up like nothing had happened, and he resumed his day as normal.”

The team decided to investigate further, and after combing through 3,600 hours of footage, they discovered three similar incidents.

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Scientists don’t know what to make of Costello’s outbursts—but one possible explanation is that he was having bad dreams.

“The behavioral sequences displayed by this octopus upon emerging from disturbed sleep were similar to behavioral responses to nightmares, night terrors and other parasomnias in humans,” they write in the paper.

The researchers caution, however, that it’s difficult to draw conclusions about the species as a whole based on observations of a single individual that might have had neurological abnormalities or other issues. Since Costello died shortly after the observations took place, it’s also possible that his behaviors resulted from senescence, or the phase before death when an animal’s cells begin to break down.

Beyond that, it would be difficult to confirm or debunk the nightmare theory by recording the brain activity of a sleeping octopus. “Where do you put electrodes on an animal that has no shape?” study co-author Marcelo Magnasco, also a neuroscientist at The Rockefeller University, tells New Scientist.

Nevertheless, the study’s authors hope other researchers will keep an eye out for similar incidents among their snoozing cephalopods. If octopuses really do have nightmares, that could suggest that “narrative dreaming independently evolved in cephalopods” and other animals, as Christie Wilcox writes for Science.

In 2021, researchers documented evidence of “active” sleep in octopuses, in which the napping animals’ skin changed color for one to two minutes roughly every half hour. It was similar to the rapid eye movement (REM) phase of sleep in humans, when dreams occur.

But researchers may never be able to truly figure out whether octopus dreams—if they dream at all—are similar to our own. Whether octopuses’ dreams have a narrative structure, or if their nighttime fantasies are somehow totally different from what we experience, remains unknown.

“It’s not something that we could easily answer,” says Robyn Crook, a neurobiologist at San Francisco State University who was not involved in the new research, to Live Science. “It’s a very philosophical question.”

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Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.