Despite these sophisticated experiments, scientists still struggle with other components of pain in animals: beliefs and expectations. How do you evaluate those things in a rat?
Imagine you have been asked to define pain by your doctor. They might have asked for a rating on a scale from zero, no pain, to 10, unbearable pain. Or you chose from a selection of faces ranging from happy to tearful. Maybe you answer with your words and gestures. You may have even drawn on a human outline found in your intake paperwork to illustrate the pain’s presence in your body.
Where does it hurt? How do you feel? The enormous number of questions a provider can ask reflects the many variables that are important for treating pain. It also makes clear that communication about pain is difficult for both patients and providers. Pain is subjective and no two experiences are alike. And, a fundamental understanding of what pain actually is has evaded science.
This is despite the establishment of numerous foundations dedicated to its study, like the International Association for the Study of Pain (or IASP), and the fact that nearly 20 percent of the United States is struggling with chronic pain. Pain’s successful escape from our grasp is due, in part, to the fact that laboratory science does not, and may not be able to, actually study pain psychology, beliefs, and expectations in animals.
In fact, we’re very careful to say in animal studies that we don’t study pain at all. We study “pain-like behaviors” after inducing an injury. The ethical limitations of such procedures are constantly evaluated so as to only induce the needed amount of “stimulus” for the purposes of an experiment. We infer from the animal’s behavior that they are experiencing pain arising from something called nociception (the phenomenon of turning a harmful stimulus, like touching a hot stove, into a signal the body can use to avoid tissue damage). But how can we learn if something is truly painful to an animal if we can’t speak with them?
Jennifer R. Deuis, a professor at the University of Queensland Institute for Molecular Bioscience in Australia, and her colleagues wrote a paper in a 2017 issue of Frontiers in Molecular Neuroscience that discusses how we investigate pain perception in lab animals through reflexes, voluntary movements, and emotional changes in animals.