Do octopuses dream like humans?

Octopuses, cuttlefish, and squids are cephalopods. The name, cephalopods, derives from the union of two Greek words, kefale and pus, which would illustratively indicate that it is an animal whose feet emerge from its head. Despite being grouped within the large group of mollusks, with snails and with mussels and scallops, cephalopods are animals we consider intelligent. Have you never seen a horror movie showing a giant mussel hunting people, but it is likely that you have heard of a giant squid watching us from the ocean depths. In fact, evidence was recently found that, in the age of dinosaurs, giant marine cephalopods almost 20 meters long, predators as large as trucks, existed. It has taken time to find these remains, because, having soft bodies, the trace in the fossil record is difficult to find and confirm.

Perhaps you also remember

the funny anecdote of an octopus named Paul, an inhabitant of an aquarium in a German city, who was consulted about the result of the 2010 Football World Cup matches and who correctly predicted which team would win in 100% of the matches in which the German team participated. Obviously, Paul did not have the power of divination, but it is true that, for more than a century, with experiments carried out at the marine zoological station of Naples, clear evidence has been found that cephalopods have short-term memory and can even learn. There are videos from aquariums showing how these animals can play with others of the same species, throwing sand, algae, and objects at each other.

Thus, it is not surprising that in many European countries, such as Spain, scientific research on cephalopods is bioethically regulated, precisely because they are considered intelligent animals and care must be taken with experimental procedures, for example, to avoid causing them any unnecessary pain. They are the only invertebrate animals that have this special consideration, along with all vertebrates, among which are mammals, such as mice and laboratory rats.

Dreaming in colors

If we look at the anatomy of octopuses, they are indeed different from us. What we consider their head, for example, would be equivalent to our torso, as it is where the three hearts (one main and two secondary) and the digestive, renal, and reproductive systems reside. The part where they have their eyes and the beak that covers their mouth would be equivalent to our head, as their brain residesthere, which are ganglia that surround their esophagus and connect to their eyes. Their nervous system is relatively decentralized: each arm has its own ganglia, right at the base, which form a circle among themselves and are responsible for movement and the perception of movement and touch. In some species, there is even regeneration of the arm or suckers.

The eyes of cephalopods are particularly attractive to us, but also to zoologists! Although our ancestors diverged about 550 million years ago, the independent evolution of the two lineages has led us to converge and present a very similar camera eye, with a retina of different neuronal layers lining the back of the eye. Many cephalopods see in color; not exactly like us, who have photoreceptors sensitive to different wavelengths of light, but because their pupil is wavy and has different refractive indices for light. Upon receiving excitation in different areas of the retina, depending on how the light reaches it, the ganglia interpret a differential pattern that gives color and shape to the reality that surrounds them. In this context, their visual perception is so accurate that their skin can change color and appearance extremely rapidly to camouflage themselves with their surroundings, acquiring apparent tones and textures so similar to the sand, rocks, or corals where the animal is found, that even to us, who have great visual acuity, it seems imperceptible.

A recent article has studied octopus when they sleep, both in terms of neuronal activity and, very curiously, skin color. Researchers have shown that cephalopods sleep and dream as we do, with different sleep stages and with differential skin color responses in response to these different stages, just as our brain also responds to the different stages of our rest. To think that these evolutionarily distant animals are capable of sharing with us the need to disconnect their brains and that, in response, their neurons connected in theoretical rest are capable of creating dreams, as ours do, is astonishing and, at the same time, makes us feel an inherent part of this natural world that surrounds us.