The octopus twitches and a pulse of yellow surges across her pale mantle. Suddenly her skin fades to a reddish black and she’s almost invisible against the dark backdrop of her tank. “Octopuses will do that when they leave the bottom,” marine biologist Dr David Scheel narrates in a short clip recently released by PBS. But this octopus is stationary, sound asleep in a tank in the middle of Dr Scheel’s lounge. She transforms again, this time her body turns a grey-washed white before morphing into mottled greens and browns. Short spikes begin to pop out of her smooth skin. In the wild, this display would be used as camouflage, perhaps to conceal a recently caught crab, Scheel suggests. If she’s dreaming, that could just be what she’s dreaming about.

The mesmerising clip – a segment from a documentary called Octopus: Making Contact – offers a unique glimpse into the endlessly fascinating world of octopus cognition and behaviour. The colour-changing starlet in the video is Heidi, a big blue octopus that Scheel recently housed in his home in the hopes of learning more about cephalopod life and intelligence. When Heidi wasn’t engaged in playful games of 'chase the ball on a stick' with Scheel’s daughter, she would sometimes snooze. And cephalopod nap time can be a dazzling affair.

To perform their colour-changing spectacles, octopuses use specialised pigment cells called chromatophores which expand and contract to transform the patterns and colours on their bodies. The optic lobe plays a key role in controlling these chromatophores. In order to blend into their marine environments, octopuses use two other cells – iridophores and leucophores – to detect the colours of their surroundings. Without these cells, it’s unlikely that the animals could match their skin to their habitats. You see, octopuses are actually colourblind, Sara Stevens, an aquarist with Butterfly Pavilion, explained to Live Science.

"The exact processes of how they match colours is still not fully understood, though it's being very thoroughly studied," Stevens said. "But current research suggests that the actual cells themselves can match colours."

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An octopus shows off its camouflage. © Jonathan Gordon

But why would an octopus change colours in its sleep? It’s possible that stimulation of the optic lobe during snoozing creates spontaneous activity that results in mesmerising colour displays, explains Jennifer Mather, a psychologist at the University of Lethbridge in Alberta, Canada.

The exact reasons for this are not yet understood, but the kaleidoscopic colour-changing show put on by Heidi is not necessarily the norm for cephalopods. In Scheel’s experience, resting octopuses often display “a pale smooth skin pattern with their arms held limply,” he told us via email. A study from 2011 shows that octopuses may also sport a half-and-half skin pattern when dozing. This not the best look if camouflage is the aim, which is perhaps why octopuses conceal themselves in dens when sleeping.

To sleep (yes), perchance to dream (maybe).

We know that octopuses (and their cephalopod relatives, the cuttlefish) are keen nappers, but we’re yet to figure out if they experience dreams. A study from 2012 found that cuttlefish display a form of rapid eye movement (REM) during periods of quiescence which could be comparable to REM sleep in humans. Dreams are typically associated with this stage of sleep, but biologists are not ready to draw conclusions on cephalopod dreaming just yet. "We have a lot of things to prove before we get there," Mather points out. "Since we don’t know much about the brain activity of octopuses, let alone what the activity would be in ‘dreaming’, I am very skeptical that anyone has any proof that ‘she was dreaming’,” Mather says when asked about Heidi’s colourful nap.

Scheel is also reluctant to draw conclusions about octo-dreaming: "The science of invertebrate sleep is still exploring these behaviours and whether we should conclude octopuses dream," he says. "My sense is that even for humans, the function of dreams is still under investigation."

Octo Intelligence

What we do know, however, is that octopuses are top of their marine class when it comes to mental complexity. In a sea of cognitive mediocrity, cephalopods are amongst the few invertebrates to exhibit superior intelligence. They have been recorded opening jars to get at snacks, carrying out daring escapes from captivity, and, in at least two cases, turning off aquarium lights by squirting jets of water at the bulbs (a pastime that cost the University of Otago in New Zealand so much money that they eventually released the octopus back into the wild).


 

Octopuses evolved to have large central nervous systems and sizeable brains. The common octopus (Octopus vulgaris) has about 500 million neurons in its body which puts it close to the range of dogs on the intelligence scale. Whether or not they are truly comparable is debatable given the octo’s unique neurological makeup.

Although the brains of octopuses and vertebrates share similar features, they are distinct in anatomy. Mammals are equipped with a single, central brain linked to a chord of nerves responsible for feeding information back to the brain for processing.

Octopus brains are spread out across their bodies. It’s unclear where they start and end. Their sucker-covered arms are effectively extensions of their brains, crammed full of neurons – twice as many, in fact, as there are in the octopus’s core brain. This spread of neurons results in a sort-of splayed out multi-brain configuration rather than the chordate, singular processing unit more familiar to humans and other mammals. Octopus arms are able to independently taste, touch and control basic motion without any input from the brain, as though each arm has a mind of its own.

Basically: octopuses are pretty smart.

This intelligence has earned them a greater level of respect in the public eye than is typically given to other marine species. So much so, that several online commenters disliked seeing Heidi confined to a tank. Scheel welcomes a discussion on the potential issues of keeping octopuses in captivity: "In my home, Heidi received the same quality of care she would have had in any public aquarium, following best practice husbandry standards and including the best equipment, food and toys as part of a rich and healthy environment that allowed her to thrive."

As soft-bodied, slow-moving animals, octopuses are at risk of predation, hence the impressive camouflage. In the wild, they spend much of their time in a den and typically do not travel far, Scheel points out. "So far as we know all animals sleep; it seems likely to me all dream," he adds "Nothing Heidi ever did made me feel she was dreaming of escape."