In a new study published earlier this month in the journal iScience, scientists found that octopuses have alternating periods of “quiet” and “active” sleep, similar to rapid eye movement (REM) seen in mammals. During rapid eye movement, the brain’s neuron activity is similar to that of waking hours. Most vividly recalled dreams take place during REM sleep.
The alternating cycle of quiet and active sleep repeated every 30 to 40 minutes. During periods of quiet sleep, the animals were pale and still, but during active sleep periods, the octopuses' skin became a darker color and their suckers also contracted.
"For around 40 seconds, they dramatically change their color and their skin texture. Their eyes are also moving," Sylvia Medeiros, a graduate student at the Brain Institute of the Federal University of Rio Grande do Norte, told NPR. "All of this happens very conspicuously."
The analysis, conducted by Sidarta Ribeiro at the Federal University of Rio Grande do Norte in Natal, Brazil, and his colleagues, was the result of recording and observing four octopuses in the laboratory for several day and night periods.
To ensure that the animals were actually asleep, researchers checked to see whether they would respond to various stimuli such as videos of swimming crabs, food items or vibrations to their tanks.
Due to the fact that the animals were found to have similar sleep patterns to birds and reptiles, which follow a REM sleep pattern, researchers speculated that octopuses might have dreams as well.
“If the octopus is having something like a dream, it’s probably a very short behavioral sequence, it’s not a narrative,” Ribeiro told New Scientist. “Whether they are having some sort of inner life with a narrative about themselves … we don’t know.”
“It would be very interesting to see what’s happening in their brains while they go from awake to quiet and then active sleep,” he added.
However, given the fact that octopuses have short active phases, the dreams are not expected to be very complex.