How science measures the subjective experience of pain in an objective way
“Pain” in the oxford dictionary is defined as a “highly unpleasant physical sensation caused by illness or injury”, but depending on who you ask- it might be defined differently. Pain, as everyone is well aware of, is a very subjective experience that is specific to an individual. What some person may consider “severe pain” may be “mildly painful” to someone else, depending on how they perceive it. Pain is usually classified as either “acute”- meaning intense and short lived- or “chronic”, which describes long-term pain. It can encompass tissue pain, such as a sprained ankle, which can cause a dull, aching feeling, and it also includes nerve-related pain, which often creates a burning, shooting sensation in the affected area. Some people say that pain is a warning sign that something is damaged, but that definition doesn’t include incidents where people experience major trauma but feel no pain. Other people define pain as the body’s way of telling you that something is wrong, but this description leaves out people who have phantom limb pain, which is felt by amputees who perceive a sensation of pain from a limb that no longer exists .
Pretty much all of us have experienced pain, and so all of us know that suffering exists on a scale. There’s intense pain such as giving birth, and then there’s small trivial pain like burning yourself with your straightener. But it’s within that range that a big question arises: how much pain are you really in? From this stems other questions, such as: can it simply be treated with Tylenol or are opioids required? Is the pain even treatable with currently available medications?
In addition to pain being highly subjective there are a myriad of things that affect ones perception of pain. For example people who are depressed, ill, out of shape, or women in general, are more sensitive to pain. Interestingly enough, we are able to tolerate more pain on the dominant side of our bodies . With such varied occurrences, it’s no wonder that pain is a challenging thing for people to describe and ultimately, for doctors to measure.
So how does the medical profession measure something that’s invisible to the naked eye? Currently, methods used to gauge pain include the McGill pain questionnaire, numerical and verbal scales, and the faces scale all of which are based on patient self-reporting. Specifically, the McGill questionnaire involves reading out a list of so-called “pain descriptors” such as “throbbing”, “excruciating”, “sickening”, and “frightful” to the patient . The patient then categorizes their pain with the allotted words, and if so, rates the intensity of the feeling. This rating gives clinicians a sense of the patient’s pain, and gives them a percentage or a number to work with when designating and assessing a certain treatment. Obviously, this method of evaluating pain has its shortcomings because some of the words may seem interchangeable to patients, and lengthy descriptions of an individual’s pain is reduced to a few words. In addition to verbally expressing pain, patients are also asked to indicate on a scale of 1 to 10, or a similar scale with facial expression how “intense” their pain is . The problem with this approach is the scale, where 10 indicates the most intense pain imaginable. How is a patient expected to imagine the worst possible pain ever? Again, depending on a persons’ past experiences and tolerance, ratings will differ. For example, women who have experienced childbirth may rate all other pain as mild, whereas someone who has never pulled a muscle might rate their pain in the intense range.
In 2013, neuroscientists from the University of Colorado-Boulder, New York University, John Hopkins University, and the University of Michigan used fMRI to map pain in the brain . Volunteers were subjected to painful doses of heat, which left patterns of brain activation. Evaluation of these patterns revealed distinct signatures, which were consistent across different subjects, and reduced in the presence of painkillers. For the first time in human history researchers were able to identify pain levels objectively.
Neuroimaging has helped fill the space between what we can see and what is being reported. Currently, researchers at Stanford University are actively studying pain with the goal of developing a database of individual patient cases so that future treatments can be more targeted. More specifically, they plan to inspect how the pain tolerance of 400 subjects of variable medical backgrounds differs over the course of five years when given various treatments.
Recent advances in brain imaging as well as methods geared towards characterizing pain are slowly reducing the obscurity of the human discussion of pain. We are still a long way from neuroimaging being the common practice to measure pain, but so far it has led to a better understanding of how the brain reacts to pain, opening the door for further investigation and ultimately, newfound application in therapeutics.