The mysterious inner life of the octopus

Octopuses are problem-solvers, mischief-makers and notorious escape artists. They also appear to have a rich inner life – so what is it like to be an octopus?

It was a big night for Inky the octopus. The day's visitors had been and gone, and now his room in the aquarium was deserted. In a rare oversight, the lid of his tank had been left ajar. The common New Zealand octopus had been without female company for some time, sharing a tank with only a fellow male, Blotchy. The loose lid provided Inky with an opportunity. With eight strong suckered limbs and, quite possibly, intimate concerns on his mind, Inky hauled himself out of the water, made his way under the loose lid, and off across the aquarium floor.

He made it about 13ft (4m) when he found something else – not a mate, but a drain that emptied into the Pacific Ocean. With that, Inky was gone.

(No one, besides Blotchy, was there to witness this great escape. But with the help of a wet trail and a few telling sucker marks, Inky's movements were later pieced together by the staff of the New Zealand National Aquarium in the city of Napier.)

As Inky demonstrated in his famous escapade, octopuses are enterprising animals adept at problem solving. They are acutely intelligent and able to learn novel tasks and orient themselves within their environment. There is also growing consensus that octopuses are most likely sentient.

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People who work with octopuses or who spend a lot of time in their company describe the sense that when you look at an octopus, there is something looking back.

"When you're dealing with an octopus who's being attentively curious about something, it is very hard to imagine that there's nothing experienced by it," says Peter Godfrey-Smith, professor of history and philosophy of science at the University of Sydney in Australia, and author of Other Minds: The Octopus and the Evolution of Intelligent Life. "It seems kind of irresistible. That itself is not evidence, that's just an impression."

Given this hunch as a starting point, how do you begin to explore the consciousness of an animal so unlike ourselves?

To start with, what do philosophers and scientists mean by "consciousness" in this context? Godfrey-Smith takes it as meaning there is "something it is like to be that animal". In a famous essay, the philosopher Thomas Nagel asks "What is it like to be a bat?" Nagel described the problem that imagining the inner experience of a bat is very difficult, if not impossible, when your reference point is the human body and your own human mind.

Likewise, imagining an octopus's inner life is a hard thing to do from our human standpoint. Try it for a moment – imagine what it's like to be suspended in the cool blueish twilight down at the seabed, perhaps a slight drag of current pulling you this way and that, your eight arms waving gently around you. When you picture the tips of your suckered limbs moving, what do you imagine it feels like? Is it, perhaps, something like wiggling your human fingers and toes?

Now add into the equation that an octopus is an invertebrate, with no skeleton at all. Its legs have no femur, tibia or fibula, no feet and no toes to wiggle. Instead, octopuses have a hydrostatic skeleton, combining muscular contraction and water's resistance to compression to generate movement. This is very different from your own experience of moving your extremities – a little closer might be when we move our tongues, which also make use of hydrostatic pressure. Indeed, the octopus's limbs are covered in suckers that have unique sensors that taste everything they touch.

"The octopus's arms are, in some ways, more like lips or tongues than hands," says Godfrey-Smith. "There's a whole great cascade of sensory information of that taste-based form that's coming in every time the animal does anything. That's very different from our situation."

Take a closer look at the octopus's nervous system, and things get even stranger. The octopus's arms have more autonomy than our human arms and legs do. Each has its own miniature brain, giving it a degree of independence from the animal's central brain. Our own nervous system, however, is highly centralised, with the brain the seat of sensory integration, emotion, initiating movement, behaviour and other actions.

"One of the real challenges we have is to try to work out what experience might be like in a less centralised, less integrated kind of system," says Godfrey-Smith. "In the case of the octopus, people sometimes ask whether there might be multiple selves present. I think it's just one self per octopus, but there might be a kind of partial fragmentation, or just a sort of looseness there."

The closer you look at the octopus's body and nervous system, the harder it becomes to grasp – or believe you are grasping – what it might be like to be an octopus. After all, the last common ancestor we shared with octopuses lived 600 million years ago (an uninspiring-looking animal something like a flatworm).

However hard it might be to do, it's worth trying to understand whether octopuses have consciousness, and what it's like if they do, says Godfrey-Smith. "We've just got to think about it, work through it and try to put together a picture."

It's a question that is becoming more urgent. The multinational seafood firm Nueva Pescanova is currently seeking licenses to open the world's first commercial octopus farm in the Canary Islands. The announcement has raised objections from animal welfare activists that it is not ethical to farm such intelligent and possibly sentient animals. As one essay puts it: "When the question of animal consciousness is under consideration, our guilt or innocence as a civilization for an enormous body of cruelty may hang in the balance."

Nueva Pescanova told BBC Future that the firm is carrying out research into the "cognitive and neurophysiological mechanisms of the octopus", and that its aquaculture conditions allow the firm "to objectively improve the octopus welfare". Nueva Pescanova says its aquaculture conditions will mimic the natural habitat of the octopus in the wild. "It is a novel system that is giving excellent results in terms of growth, survival and endowment of the specimens," a spokesperson for the firm says.

As Heather Browning, a postdoctoral researcher in animal sentience and welfare at the London School of Economics, argues in an essay: "The mind of an octopus may be highly different from our own, but it is only by trying to see the world from their point of view that we will be able to find out what is good for them and hence ensure their welfare."

Browning, who is working on a project on the Foundations of Animal Sentience at LSE, was part of a team that sought to answer the question of whether octopuses are conscious in an influential report.

One approach is to start out with a case study for something we know is sentient: other human beings. "If we really get down to it, we assume that we are sentient ourselves, and we assume that other humans are like us as well, which I think is really reasonable," says Browning. "From there, you can start looking at features that other animals might have in common with us."

Take, for instance, the ability to feel pain – the focus of the LSE team's report on cephalopod molluscs (which include octopuses, cuttlefish and squid) and decapod crustaceans (which include crabs, crayfish, lobsters, prawns and shrimps). Browning and her colleagues reviewed more than 300 scientific papers to distil eight criteria that suggest an animal can feel pain:

An animal can meet a criterion with a high, medium or low level of confidence, depending on how conclusive or inconclusive the research is. If an animal meets seven or more of the criteria, Browning and her colleagues argue there is "very strong" evidence that the animal is sentient. If it meets five or more with a high level of confidence, there is "strong evidence" of sentience, and so on.

Using this measure, Browning and her colleagues concluded that there was little doubt octopuses could feel pain, and were therefore sentient. They met all but one of the criteria with high or very high confidence, and one with medium confidence. They scored most highly out of the creatures studied – more so even than their cousin the cuttlefish, who are considered to be more intelligent. (Browning notes, though, that far less research has been done on cuttlefish and other cephalopods besides octopuses, which affects their scores.)

The report was used as evidence to inform an amendment to the UK's Animal Welfare (Sentience) Bill to recognise that cephalopod molluscs and decapod crustaceans are sentient.

"I think that's a good thing, the fact that in the UK octopuses and also crustaceans are getting a new kind of recognition in animal rights," says Godfrey-Smith.

The ability to feel pain is just one of the many facets of consciousness – there is also the ability to feel pleasure, to feel bored or interested, to experience companionship, and many more. With more research, scientists may be able to devise similar scales to measure more of these different aspects of consciousness in animals.

There is a second line of evidence, besides looking for what correlates with human experience. That is to consider the biological role of consciousness and why it evolved. "This is something that people are just starting to question," says Browning.

One possibility is that consciousness evolved alongside behaviours such as complex types of learning, decision-making and making motivational trade-offs (do you risk nipping out from under your shelter to grab at a passing morsel, even though you saw a predator about earlier?). It's complex situations like this that might give rise to the sense of experience.

"There are some things that people think, at least in the human case, you can't do unconsciously," says Godfrey-Smith. "These include responding in an intelligent way to novelty."

Sometimes when presented with a novelty, such as a lever in their tank, octopuses respond with an ingenuity all of their own. For experimenters, this originality can get a little frustrating.

In one experiment from 1959, the psychologist Peter Dews trained three octopuses – which he named Albert, Bertram and Charles – to pull a lever in their tank, which lit up a bulb and released a small piece of fish. Albert and Bertram learned how to do this without a great deal of difficulty. Charles, however, was more obstinate. Dews wrote: "Charles anchored several tentacles on the side of the tank and others around the lever and applied great force. The lever was bent a number of times, and on the 11th day was broken, leading to a premature termination of the experiment."

As well as being "particularly feisty", as Godfrey-Smith puts it (Charles got into the habit of squirting water jets at anyone who came near his tank), the octopus showed a marked interest in the light bulb, which Albert and Bertram largely ignored. Charles, however, encircled the light with his tentacles and carried it off into his tank.

Such examples of attentive curiosity are telling, according to Godfrey-Smith. "Some of the leading theories of what consciousness is in animals agree that a kind of attentive orientation to things is not the kind of thing that can occur unconsciously in us, or it seems other animals," he says. "So that's a mark highly suggestive of experience."

If the octopus is indeed sentient, it still leaves open the bigger question: what is it like to be an octopus? Part of the reason this is so difficult to answer is that science doesn't provide results in a useful form for assessing subjective experience, says Marta Halina, an associate professor in the department of history and philosophy of science at the University of Cambridge.

"What it is like to be an organism from that organism's first-person perspective – we don't have access to that," says Halina. "Science takes the third-person perspective on systems – and so we have a problem."

Making this leap from the objective to the subjective has become known as "the hard problem of consciousness" (see box to the left).

There may be no neat solution to the hard problem yet, but there are one or two practical ways around it. One is to look at "behavioural correlates" or "neurological correlates" of consciousness – in other words, behaviours and neural systems that we suspect are closely related to conscious states. "We can use those as markers of consciousness," says Halina. (This is what Browning and her colleagues at LSE did, using markers such as the presence of nociceptors.)

There is a risk, however, that we get bogged down in our own human perspective. "We're most certain about human consciousness and so often the neurological correlates and behavioural correlates that we're relying on are grounded in the human case," says Halina. "The further we move away from humans in terms of structure and behaviour and function, the less certain we are that we're actually tracking consciousness."

For instance, if you look at an organism like the fruit fly and search for a human-like neural system for sensing and responding to pain but don't find it, this doesn't rule out that the fruit fly is able to feel pain. "It just means that they might do it a little differently," says Halina.

This is why the octopus is such an interesting case – it can be seen as a form of "conscious exotica", or an example of consciousness very unlike our own, as Halina writes in an essay on the subject. Octopuses are different enough from us that a lot of our assumptions about them have to be questioned – and even our assumptions about ourselves.

"By asking whether octopuses are conscious like us, we might be asking a question that doesn't make a lot of sense because we don't fully know what it's like to be conscious," says Halina.

She uses the example of a technique borrowed from the consciousness researcher Susan Blackmore, in which she sets the task of asking yourself the question "am I conscious now?" throughout the day, whenever it occurs to you – on the verge of sleep, eating breakfast, or in the midst of conversation.

"You find that you're not so confident about what consciousness is at any given moment," says Halina.  

As well as learning more about octopus's consciousness for their own welfare in the light of commercial farming, their minds may also tell us something about ourselves.

"It's valuable to consider what it's like to be an octopus because that can lead us to re-evaluate what it's like to be a human," says Halina. "And maybe reflecting on how little we know about what it's like to be a human can lead us to be more open about what it's like to be an octopus."

* Martha Henriques is Editor of BBC Future Planet, and tweets at @Martha_Rosamund

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