The mysterious inner life of the octopus

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:

1. possession of nociceptors (receptors that detect noxious stimuli – such as temperatures hot enough to burn, or a cut)
2. possession of parts of the brain that integrate sensory information
3. connections between nociceptors and those integrative brain regions
4. responses affected by local anaesthetics or analgesics
5. motivational trade-offs that show a balancing of threat against opportunity for reward
6. flexible self-protective behaviours in response to injury and threat
7. associative learning that goes beyond habituation and sensitisation
8. behaviour that shows the animal values local anaesthetics or analgesics when injured

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.

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