Octopuses may have nightmares. That is one possible explanation for some extraordinary behaviour caught by cameras monitoring an octopus in a laboratory aquarium, says at the Rockefeller University in New York.
In 2021, his team bought an octopus (Octopus insularis) caught off Florida for their studies of cephalopod cognition. The octopus, named Costello after one of the 鈥渉eptapod鈥� aliens in the film Arrival, rapidly adapted to captivity and began sleeping out in the open, rather than in a den as octopuses do in the wild.
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One morning, team member Eric Ramos, also at the Rockefeller University, entered the room with the aquarium and noticed that the water was cloudy with ink. He checked the camera footage to see what had happened.
It showed that Costello had been sleeping quietly on the side of the tank, which he shared only with tiny fish. For no apparent reason, he suddenly began thrashing around, tried to make himself look bigger by extending his mantle into a cone shape and released ink, as if he were being attacked by a predator.
鈥淚f you admit that an invertebrate can have dreams, then a nightmare is a no-brainer,鈥� says Magnasco. 鈥淭he life of an animal in the wild can be hard.鈥�
Before being caught, Costello had lost a tentacle to a predator. 鈥淗e had a rough life,鈥� says Magnasco.
When the team looked through hundreds of hours of footage of Costello, they found three similar but shorter events.
It remains unclear whether octopuses do dream in the same way that we do, says Magnasco. While sleeping, their skin usually goes pale and they remain motionless. But for short periods, their skin colours change while they are sleeping.
A 2021 study of four common octopuses (Octopus vulgaris) by Sidarta Ribeiro at the Federal University of Rio Grande do Norte in Brazil and his colleagues showed that this colour-changing sleep phase occurs every half an hour or so during sleep, and lasts 1 or 2 minutes. As well as the animals鈥� skin changing colour and texture, their eyes and tentacles move as well.
This means it resembles the rapid eye movement (REM) sleep stage during which people dream. But monitoring octopuses to see if their brain activity is similar, too, is extremely difficult. 鈥淲here do you put the electrodes on an animal that has no shape?鈥� says Magnasco.
Even if cephalopods do dream, another big question is whether their dreams have the narrative structures characteristic of human dreams 鈥� that is, whether they imagine some sequence of events.
In , at Alaska Pacific University noted that a sequence of colour changes exhibited by his pet octopus, Heidi, while sleeping resembled those that would be seen if she were capturing crabs and speculated that this is what she was dreaming about.
Costello鈥檚 anti-predator responses all occurred immediately after this colour-changing sleep stage. His behaviour could be a form of sleepwalking, or parasomnia, says Magnasco. It might also be related to ageing 鈥� Costello was old in octopus terms at the time.
No conclusions can be drawn from a few episodes involving a single individual, Magnasco stresses, and there are also other possible explanations. Costello might have had seizures, for instance 鈥� though Magnasco isn鈥檛 aware of any records of seizures in invertebrates.
He hopes other teams will now look out for such behaviour and help determine what is happening.
鈥淎lbeit speculative, I think that the nightmare hypothesis is not unlikely and does deserve further investigation,鈥� says Ribeiro, who wasn鈥檛 involved in the study but has seen the footage.
If narrative dreams do turn out to have evolved independently in cephalopods, it would suggest they are essential in advanced brains, says Magnasco. 鈥淚t means it really is a strong requirement for some cognitive purpose.鈥�
bioRxiv
