Science & Technology | Octopuses, Dreams and Cognition
Octopuses may have nightmares
Uncovering the mystery of sleep
Because animals can’t talk, proving that they dream is tricky. Neurologists began assuming they were capable of it in the 1950’s when mammals such as dogs, cats and platypuses as well as birds and reptiles were found to have Rapid-Eye Movement (REM) sleep. In humans, this is the sleep stage during which one dreams. But it was the discovery that people who suffer from REM Sleep Behaviour Disorder violently act out their nightmares via kicking, punching and jumping out of bed that prompted French researchers to investigate whether this also applied to cats. After removing the part of their brain stem that controls paralysis, the cats in question were found to behave aggressively in their sleep-similar to how they would act while chasing mice during the day. As a result, dreaming was no longer considered uniquely human, the observation of sleep behaviour becoming a method to identify dreams in animals.
Using this approach, Marcello Magnasco at the Rockefeller University in New York has come one step closer to proving that octopuses do not just have the capability to dream but also to experience nightmares. His research team produced video footage of ‘Costello’, an octopus they were monitoring as part of a cognition study, thrashing around and releasing ink for no observable reason shortly after waking. Squirting ink into the water is a camouflage mechanism usually adopted by octopuses as a means to hide themselves while under attack-given that Costello was not reacting to any external stimuli at the time, the idea that he was dreaming of a predator attack seems plausible.
A 2021 study conducted by Sylvia Medeiros at the Federal University of Rio Grande de Norte in Brazil previously established that octopuses have two distinct sleep stages, a ‘quiet’ and an ‘active’ one. During the latter, they would change colours and skin patterns, contract their suckers as well as move their eyes, the latter mannerism reminiscent of the sideways movement of eyes during human REM sleep.
Nonetheless, the results of both studies do not conclusively prove that octopuses can dream. Costello’s behaviour could be a simple sign of aging, the uncoordinated movements caught on camera being a typical sign of deterioriation in the species prior to their death. In the case of the octopuses observed by Medeiros, not all were confronted with external stimuli to check for wakefulness, some only being observed during the quiet stage, prompting speculation that they were, though drowsy, still awake while changing the colour as well as pattern of their skin.
Confirming that an octopus can dream would entail monitoring its neural activity within the active stage and assessing whether it corresponds to that of humans during the REM stage. This is not feasible, however, as electrodes cannot be attached to organisms without solid body parts. Yet recent strides in neural recording devices that can be directly implanted within the brain of an octopus offer some hope for future sleep research studies involving the highly sentient beings.
Medeiros already plans to conduct new studies with octopuses, the aim being to discover whether sleep helps octopuses store relevant information as well as learn new tasks. This line of research is in keeping with the dominant theory regarding the evolutionary purpose of sleep-namely, that it is a tool to help sift through daily experiences to find and replay information that needs to be retained. Should this be the case for octopuses, it would serve to support the hypothesis that both sleeping and dreaming is essential for the development of complex forms of intelligence across the species barrier.
