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Octopuses Get Emotional About Pain, Research Suggests

The smartest of invertebrates, the octopus, once again prompts us to rethink what we believe to be the origin of intelligence

The octopus is becoming a popular creature among neuroscientists. It is a very smart invertebrate with an unusually complex nervous system, organized in a fundamentally different way from that of, for example, mammals. Recently, a researcher has found the first strong evidence that octopuses feel pain, as opposed to merely reacting to it.

There are two parts to pain: The natural physical reaction, like a sophisticated alarm system, sets off a chain of involuntary responses. But that chain of responses, by itself, doesn’t prove that any “self” is feeling anything. The alarm system would work just the same in an empty building as in a populated one.

The second component can be called “emotional.” The life form experiences the pain in a unified way as undesirable. That is like people in the building rushing either to or from the scene of the emergency, in response to the alarm. The alarm does not program them to automatically do that. They are doing it in response to anxiety and the need to protect life. Generally, invertebrates like octopuses were not thought to feel things in that sense.

How could we know whether an octopus feels pain? One enterprising researcher decided to put octopuses through a test developed to study pain responses in lab rats. Would the octopuses behave the same way? San Francisco State University neurobiologist Robyn Crook found that

After a single training session in a three-chambered box, octopuses that received an injection of acetic acid into one arm showed clear avoidance of the chamber in which they received that shot.

Those injected with non-harmful saline, on the other hand, showed no such avoidance.

Furthermore, when the octopuses that had been given a painful injection were then administered lidocaine (an analgesic), they tended to prefer the chamber in which they experienced immediate pain relief. Those that received saline only couldn’t care less about the chamber where they had analgesic applied.

Carly Cassella, “Octopuses Not Only Feel Pain Physically, But Emotionally Too, First Study Finds” at ScienceAlert (March 5, 2021) The paper is open access.

So the octopuses learned to avoid circumstances that, without harming them, gave them pain. They reacted more strongly to greater pain.

There is a level at which we can perhaps never know whether octopuses feel pain in an emotional sense. But wait, we have just the same problem with lab rats! We don’t know what it is like to be a sentient but not an intellectual being. Perhaps rats and octopuses suffer less than we do but they could also suffer more.

Contrary to what we might think, an active intellect typically suppresses and contains pain, rather than magnifying it. Dr. Michael Egnor explains, in relation to human babies vs. adults: “Certainly anyone who is had any experience with very young or premature infants can attest that children at this age seem to experience pain quite intensely. I have cared for hundreds of premature infants and it is very clear that these very young children experience pain intensely. An innocuous needlestick in the heel to draw small amount of blood would ordinarily not be particularly painful for an adult. But a tiny infant will scream at such discomfort.” Of course, the infants are humans. But they are humans whose intellects are as yet undeveloped so they can’t localize and contain the pain very easily.

Crook’s research shows that we have no clear basis for assuming that octopuses suffer less than lab rats do. One issue that arises for research labs is whether the use of intelligent vertebrates like octopuses in experiments should be regulated, for humanitarian reasons, in the way that the use of vertebrates is:

Whether cephalopods (and other invertebrate animals) can experience the emotional, affective component of pain (i.e., to know that a noxious sensation is unpleasant or distressing, rather than simply responding via unconscious, behavioral reflex), has always been an unresolved question. The newest work from our lab uses a widely validated assay for studying the affective component of pain in laboratory rodents, to show that octopuses behave the same way. The most parsimonious explanation for the behavior of the octopuses in this experiment is that they are capable of the negative affective state that characterizes pain experience in mammals. This is the first conclusive evidence for this capacity in any invertebrate.

Pain in cephalopods” at Crook Laboratory

How would we know that a life form does not really feel pain — that its behavior is simply programmed reactions? One clue might be if, unlike the octopus, it lacks a brain and/or any sign of individuality. The question then becomes, “If pain were felt, what, if anything, would be feeling it?” Perhaps such a life form has a sophisticated alarm and self-repair system in an otherwise empty “building.”

What we do know is that octopuses (and their cousins, squid and cuttlefish) seem to be outliers among invertebrates, in terms of intelligence. They have been called a “second genesis” of intelligence.

Highly intelligent invertebrates like these challenge our ideas of how life forms come to be intelligent. For one thing, unlike most intelligent life forms, octopuses are unsocial and short-lived. Some researchers think that octopuses were forced to become intelligent when, unlike their nautilus cousins, they lost their shells:

Losing their shells also made the cephalopods exquisitely vulnerable. One scientist described their soft, unprotected bodies as the equivalent of “rump steak, swimming around.” The rest of the ocean seemingly agrees: Almost every major group of predators eats cephalopods, including dolphins, seals, fish, seabirds, and even other cephalopods. This gantlet of threats might have fueled the evolution of the cephalopods’ amazing color-changing skin, their short life spans, and their large brains. After all, intelligence can help an otherwise defenseless creature create new defenses, as Blue Planet II’s shark-defeating octopus so ably showed.

It’s telling that the nautilus—the only living cephalopod that still has an external shell—bucks all of these trends. It lives for up to 20 years, reproducing several times during its life. It also has a much smaller brain than its shell-less relatives, and doesn’t seem to be anywhere as smart.

Ed Yong, “For Smart Animals, Octopuses Are Very Weird” at The Atlantic The paper is open access.

Well now, there’s an animal intelligence hypothesis we can test: Will we ever find a shelled creature that is as smart as the octopus?

Meanwhile, what to make of Ed Yong’s suggestion, “This gantlet of threats might have fueled the evolution” of octopus intelligence? Need alone does not by itself produce intelligence any more than fear of death by itself produces longer natural lifespans. A creature that needs intelligence but doesn’t have it might just as likely go extinct. There are some significant unknowns we need to fill in here.

This is bound to be a fascinating research area.

You may also wish to read:

Is the octopus a “second genesis” of intelligence? Can its strange powers provide insights for robotics or the human mind?


Scientists clash over why octopuses are smart New findings show, the brainy seafood breaks all the rules about why some life forms are smart.

Denyse O'Leary

Denyse O'Leary is a freelance journalist based in Victoria, Canada. Specializing in faith and science issues, she is co-author, with neuroscientist Mario Beauregard, of The Spiritual Brain: A Neuroscientist's Case for the Existence of the Soul; and with neurosurgeon Michael Egnor of the forthcoming The Immortal Mind: A Neurosurgeon’s Case for the Existence of the Soul (Worthy, 2025). She received her degree in honors English language and literature.

Octopuses Get Emotional About Pain, Research Suggests