Octopus Heidi went viral in 2019 with a video which showed how she changed color asleep. Biologists wondered what was going on here. Is she dreaming?
Researchers from the Federal University of Rio Grande do Norte in Brazil took a closer look at the strange behavior. In the scientific journal iScience they now conclude that octopuses have two phases in their sleep cycle: a silent and an active one.
To prove this, the researchers made videos of octopuses in the lab. When the octopus is asleep, the two stages alternate. In silent sleep, the octopus lies motionless and is white in color. The difference with active sleep couldn’t be greater. The octopus constantly changes its color pattern and also its skin texture. Its suction cups contract and its tentacles jerk.
Can we speak of sleep in that active phase? The researchers tested this by measuring the octopus’s response to external stimuli, such as touch or bright light. Only when the researchers gave the octopus very strong stimuli did he react. In other words, he was really sleeping before that.
Evolved independently
Previously, biologists believed that only mammals and birds have two stages of sleep. In humans this is, for example, REM sleep and non-REM sleep (‘REM’ stands for rapid eye movement, rapid eye movement). Recent scientific research shows that this sleep cycle also occurs in reptiles, and now also in invertebrates. They are far removed from humans in the evolutionary family tree, our evolutionary branch split off 500 million years ago. The researchers therefore believe that octopuses’ sleep cycle evolved independently, although it is so similar to that of humans.
Sander Griepsma, biologist at the Sea Life aquarium in Scheveningen, is ‘glad that this has been properly researched once’. According to Griepsma, octopuses’ sleep patterns are linked to their intelligence. For example, they can open shells, build fortresses of stones to spend the night in, and turn the lids of pots. And anyone watching the Netflix documentary My Octopus Teacher knows how curious and eager to learn they are. ‘Animals with higher brain functions probably have more to process. For that they need more complex processes during their sleep. ‘
In humans, we know that this processing takes place during REM sleep. That comes with dreams. Would the octopus’s active sleep work similarly? ‘Of course we cannot ask them whether they have dreamed, which is possible with people.’
Flupsma suggests following the octopuses during their waking hours in another experiment to see if their dreams are about their previous activity. ‘Suppose they were sitting on a red rock earlier in the day. Do they also turn red during active sleep? ‘
–
–
