The past couple posts have described some pretty severe experiments on octopuses, including: showing how octopus arms can grow back after inflicted damage and how even severed octopus arms can react to stimuli. (For the record, animals in the studies were anesthetized and euthanized, respectively.) Without getting too far into the woods (or reefs) of animal treatment ethics, the question remains: How much pain and distress can these relatively short-lived invertebrates experience?

Luckily for us, a new paper deals with that very question. Researchers from Europe, the UK and Japan teamed up to explore what we know about pain, perception and cognition in octopuses. The findings are described in the special “Cephalopod Research” issue of September’s Journal of Experimental Marine Biology and Ecology.

And the issue is not just philo-scientific cloud (or wave) gazing. Starting this year the European Union asks researchers to make similarly humane accommodations for cephalopods as they do for vertebrates (Directive 2010/63/EU, pdf). But, do octopuses experience would-be painful experiences the same way mice do? As the researchers note in their paper, we know very little about whether cephalopods recognize pain or experience suffering and distress in a similar way that we humans–or even we vertebrates–do.

Previous (as well as much current) research has looked largely to behavioral clues as an indication to an octopus’s internal state. For example, researchers have observed an octopus’s color changing and activity patterns and looked for any self-inflicted harm (swimming into the side of a tank or eating its own arms) to judge whether the animal is “stressed.” And to tell whether an animal has “gone under” anesthesia, they often look for movements, lack of response, posture change or, at the most, measure heart rate and breathing.

But these are still relatively rough measures of a complex process. And “there are strong ethical, legal and scientific obligations to avoid, recognize and alleviate any pain, suffering and distress caused to animals used in scientific procedures,” the researchers note.

In our own experience, three major elements are involved in feeling pain. First, there is the detection of physical pain (via receptors known as nociceptors). Second, there is the experience of pain (which, in our case, is mediated by the cerebrum). And finally, there is the crucial step our bodies take in communicating the information from sensation to perception. Do octopuses possess enough of these features to feel anguish as we do? (This is a fascinating question for many animals–especially those we occasionally eat; David Foster Wallace’s famous essay “Consider the Lobster” explores the issue for crustaceans.)

Octopuses likely have nociceptors, as demonstrated from their withdrawal from noxious stimuli (even in severed arms) and suggested by the fact that there is good evidence that even “lower” mollusks possess them. But research has not yet confirmed their presence. And, at least during hunting, an octopus that is pinched by a crab will not withdrawal but will, rather, proceed with its attack, the researchers note.

If they do have these key receptors, do they have the mental complexity to compute a deeper sense of displeasure? “Higher cognitive abilities are considered important for the presence of sentience and the capacity to experience pain, suffering and distress,” the researchers write. Octopuses’ central brains are organized in an unusually sophisticated way for an invertebrate, possessing distinct lobes. And they are capable of learning, discrimination, spatial awareness and impressive memories. But we do not yet have evidence that they can process suffering as we do.

Finally, research showing efficient transmission of incoming, would-be painful stimuli from the skin to the lobes of the central brain actually seems to be the most lacking. Octopuses are wired unlike most other familiar animals. Their arms contain their own, individual small “brains,” and arms seem to communicate with each other via a lower nerve connection that does not pester the brain with mundane movement and coordination tasks. Both of these could explain why an octopus arm might recoil at an unpleasant sensation without the animal having a “conscious” experience of it. Cuttlefish apparently remember “distasteful” prey, suggesting the use of the central brain in relation to an unpleasant stimulus. But whether “pain”–especially originating from an arm–is processed in the central brain remains to be determined.

Much more research is needed. However, the catch-22 for this type of work is that pursuing it “may involve procedures with the potential to cause pain, suffering and distress,” the researchers write. This “creates an ethical dilemma given that the ultimate aim would be to reduce suffering for cephalopods.”

Certainly some awareness of harmful stimuli is important for an animal to survive and thrive. As the authors point out, experiments showing that cephalopods can learn via electric shocks as a negative stimulus are suggestive that the octopus has felt–and remembered the sensation. But “responses might not be mediated by nociceptors (or could involve a variety of receptors) and hence might be a different kind of aversive sensation, when compared with pain experienced in humans,” the authors note.

And as the authors of this review remind us, “care must be taken in drawing conclusions between cephalopod and vertebrate brains, as the last common ancestor of vertebrates and cephalopods existed over 500 million years ago.”

Illustration courtesy of Ivan Phillipsen