What difference would it make, if we could measure pain? We usually learn what pain is from our earliest experiences of physical tissue damage. It may also have a psychological or emotional basis.
Pain can described as a subjective felt experience because it is influenced by an individual’s feelings, mind, and experience. That’s also why it can be so tricky to diagnose and treat. It is so intangible.
Limits of the Visual Analog Scale
When working with adults in my clinical practice who suffer from acute or chronic pain, I often use the Visual Analog Pain Scale (pain levels of 1-10) to both evaluate levels of pain and to measure the effectiveness of a treatment protocol. Health insurance companies repeatedly challenge practitioners to justify the need for treatment. Ultimately, the patient loses because it is so difficult to measure or verify the type of pain being experienced which can interfere with patients getting the help they need.
There also is the most vulnerable population to consider, those who may not be able to describe their discomfort because they are either too young or elderly, minimally conscious, or cognitively impaired.
All together, these factors beg the question, is pain a measurable experience? If it could be measured, what impact would that have on diagnosing and managing it?
Tor Wager’s fMRI Pain Measure Studies
In a series of four studies, Tor Wager and colleagues set out to objectively measure and predict pain intensity through the use of functional magnetic resonance imaging (fMRI) brain scans. Their findings look to be a game changer.
In the first study, 20 normal, healthy human subjects were exposed to varying levels of heat and then their brains were scanned in order to identify which brain structures were involved and whether any identifiable patterns would emerge. What they discovered was a neurological signature for heat-induced pain, that is, specific brain regions consistently lit up more than 94% of the time. The signature was discovered to be specific to pain and sensitive to changes in heat intensity. Brain maps were generated from these initial findings and then applied to new participants in Study #2, in an effort to predict pain.
In the second study, the neurological signature identified in Study #1 was tested with a new group of 33 participants. This study aimed at predicting pain by measuring its intensity through the ability to discriminate between painful heat and non-painful warmth across six temperatures. The researchers were able to show that the signature response increased as the pain intensity increased, resulting in the creation of a code using a 100-point Visual Analog Scale that was about 93% accurate. The results suggested that the neurological signature was measuring the subjective sensation of pain as well as the intensity of somatic stimulation. They also found that the signature response discriminated between intense and mild non-painful warmth. This is a very significant finding because it may be useful in further studies of allodynia or hyperalgesia, two unusual types of pain.
The third study was a test for specificity. The researchers took the results of the first two studies involving the mapped neurological signature and the ability to predict pain, and added in the new component of social pain. In this case, 40 participants were studied who had recently experienced a romantic break-up and were still suffering from feelings of rejection. In addition to being exposed to painful and non-painful heat, they also viewed an image of a close friend and an image of the “rejecter.” Which brain structures would be involved now? While researchers were able to discern that regions for physical and social pain were both activated, the neurological signature still clearly discriminated between physical pain and social pain.
This study explored how the neurological signature for pain would respond to the administration of the opiod agonist remifentanil during fMRI scanning. The goal was to elicit analgesia without sedating the participant while they were exposed to a painful heat stimulation or a warm stimulation. They found a parallel response, that as the effects of the drug on the brain increased, the signature response decreased up to 53%.
Why This Study is Important
This study successfully identified a fairly universal and reliable neurological signature brain pattern for heat-associated pain. It also validates earlier studies aimed at measuring sensitivity and specificity for pain using fMRI scans. More studies are needed before it can become clinically useful. Since the study was done with healthy persons, there is much work to be done in assessing individuals who are in pain. Although the task is daunting and there are so many variables, this study makes a very important contribution.
An fMRI-Based Neurologic Signature of Physical Pain by Tor D. Wager, Ph.D., Lauren Y. Atlas, Ph.D., Martin A. Lindquist, Ph.D., Mathieu Roy, Ph.D., Choong-Wan Woo, M.A., and Ethan Kross, Ph.D. N Engl J Med 2013; 368:1388-1397April 11, 2013DOI: 10.1056/NEJMoa1204471
The researchers used data-mining algorithms to search for brain patterns in subjects who were exposed to different levels of heat. What they found was surprising. Instead of the patterns being unique to each individual studied, they found that pain patterns manifest as neurological signatures across multiple brain structures.