An octopus explores the Conditioned Place Preference box. ©CrookLab
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.
Knowing the answer to this question is more than just a scientific curiosity; it is essential to advancing moves to treat cephalopods more humanely in whichever context they encounter humans - in research labs, but also in zoos, aquariums and in fisheries.
We recognize that research work on pain in animals like cephalopods, with their highly complex brains, is controversial. However, the lack of clarity on the question of whether invertebrate animals can suffer as a result of noxious sensory input continues to hamper efforts to improve their welfare. Our goal with this study was to move the question of invertebrate pain beyond reasonable doubt, so that efforts to better regulate their humane use can proceed with a strong evidentiary foundation that until now, has been lacking.
Evidence for vertebrate-like pain experience in invertebrates has been inconsistent and focused mostly on crustaceans and insects. Some studies supported the hypothesis that the emotional component of pain was present in invertebrates and some did not; there have been very few studies that took validated assays for measuring pain in vertebrate animals and applied them to invertebrates, leaving room for the interpretation that the experimental evidence was insufficient proof of an equivalent emotional state underlying equivalent behavior. In this paper we show that not only can vertebrate specific protocols for testing pain’s presence and absence be adapted to cephalopods, they can reveal the same evidence for internal state.