The octopus is a mysterious creature. It has three hearts, and blue blood, not red, runs through its veins. Its skin can detect light and chemicals, and some species can even regrow severed arms. But there is another reason scientists pay particular attention to octopuses: the brain.
Animals with multiple arms attached to their heads, such as octopuses, squid and cuttlefish, are known as cephalopods. Cephalopods are rare among invertebrates in possessing a sophisticated nervous system. They have excellent memory, can use tools and solve problems to obtain food. Like pet dogs or cats, they also display behavior such as waiting for a reward. How did the octopus come to have such intelligence?
Cephalopods With Strong Learning Abilities Draw Long-Standing Scientific Interest
The international journal Nature recently reported that neuroscientists are studying cephalopods to trace an alternative path in the evolution of intelligence. Humans and octopuses diverged in the very distant past. Nevertheless, octopuses display complex behavior and learning ability. This serves as an important clue that intelligence does not evolve only in the way it has in humans or mammals.
The octopus brain is shaped like a donut. It has a unique structure in which the esophagus passes through the middle of the brain. More than half of the total neurons are distributed not in the central brain, but in the nerve cords controlling the eight arms. Each arm effectively operates as a kind of "small brain." Octopus arms may appear to move erratically, but in reality, they use their suckers to precisely explore their surroundings and detect prey.
The octopus's visual processing is also of interest to scientists. Octopuses have excellent eyes, but it is not yet fully understood how the brain interprets information received through them. Recently, dopamine receptors that function differently from those in vertebrates were discovered in the octopus visual system. This suggests the possibility that the cephalopod brain is solving problems similar to those of humans in entirely different molecular ways.
In fact, neuroscience already owes a great debt to cephalopods. In 1929, British zoologist John Zachary Young discovered giant nerve fibers in squid. These nerve fibers, up to 1 millimeter wide, were suitable for studying nerve signals by inserting electrodes. Based on this, scientists later uncovered the fundamental principles of how neurons generate electrical signals, laying the foundation of modern neuroscience.
Recent researchers are examining whether octopuses use cells similar to the "place cells" of mammals when finding their way, and what kinds of computations cuttlefish brains perform when changing skin color to match their surroundings. Cuttlefish can change their skin patterns and colors in just a few seconds. Scientists expect that analyzing this process will reveal how the cephalopod brain perceives and judges the surrounding world.
There are also claims that octopuses dream. A Japanese research team observed sleeping octopuses rapidly changing their skin color and suggested the possibility that octopuses may be replaying visual experiences even during sleep. This could be similar to the phenomenon in which the human brain recalls the day's experiences during dreaming.
Can Smart Octopuses Be Used in Experiments? Ethical Issues Emerge
However, using octopuses as experimental animals is not easy. Breeding and rearing them is difficult, and their irregular movements make it hard to stably record neural activity while they are alive. Ethical issues are also growing. Experiments on vertebrates are covered by relatively comprehensive legal protections, but invertebrates often are not. Still, voices are growing that research standards to reduce pain and stress are needed even for creatures with complex brains and behaviors such as octopuses. Indeed, some countries now include cephalopods among animals protected under experimental regulations.
Octopus research may not be a shortcut to directly explaining the human brain. Rather, it is the opposite. Octopuses show that even with bodies and nervous systems entirely different from those of humans, they can remember, judge and adapt to their environment. This is why scientists look into the octopus brain. Intelligence did not evolve along only one path. The octopus is quietly proving that fact beneath the sea.
