Fibromyalgia is a chronic disorder that causes pain and tenderness throughout the body, as well as fatigue and trouble sleeping. Scientists do not fully understand what causes it, but people with the disorder have an increased sensitivity to pain.
This specific area of Harper’s focus — pain — is notoriously difficult to study. As Harper, an assistant professor of anesthesiology in the Emory University School of Medicine, explains, each person’s perception of pain is entirely subjective. This leaves researchers and physicians alike with no objective way to measure it. A patient’s ranking of their pain on a scale of one to 10 is often the best gauge.
One of the reasons pain is so hard to measure has to do with how the sensory system in the body is organized. Nociceptors alert a person to pain while innocuous somatosensory receptors alert a person to non-painful stimuli like touch and temperature. The problem for pain researchers is that the innocuous receptors are much more sensitive than the nociceptors, which allows someone to feel the sensations of hot, cold and pressure without feeling pain.
Because people cannot reliably tell when their nociceptors have been triggered, researchers don’t know if subjects are reacting to stimulation of innocuous receptors or nociceptors.
This conundrum has stumped pain researchers for decades, but in his Psychophysics and Imaging Neuroscience (PaIN) Lab, Harper has developed a novel method to selectively stimulate nociceptors without activating any innocuous receptors. His work takes advantage of the fact that the innocuous receptors that detect heat are the least concentrated of any fiber type in the skin. Using a thermal contactor, Harper is able to scan a subject and find fairly large areas of skin totally devoid of innocuous warm fibers. He can then apply a warm stimulus to that area and increase its intensity until the nociceptors are triggered. Finally, he can increase the heat until the subject reports the stimulation of their nociceptors as painful.
In his current study, Harper will compare the reactions of subjects with fibromyalgia to a control group to determine if the nociceptors in people with fibromyalgia are hypersensitive.
Harper’s subjects will also receive the stimulation while they are in an MRI scanner, which will measure the underlying brain activities associated with the stimulation of nociceptors in different areas of the brain. The interpretation of this brain activity will be simpler because the picture will not be muddied by additional signals coming from the innocuous system. “This is a much cleaner way to measure the processing of pain signals in the brain, enabling us to measure a ‘pure pain’ signal.”
While his current study focuses on fibromyalgia, Harper believes this novel method of pain measurement could be useful across a host of other conditions. “My goal for this technique would be to make it easy for researchers to put the protocols out there in an open science framework,” says Harper. “That way, researchers all over the world could use this technique to measure the sensitivity of nociceptors in a noninvasive, unbiased fashion. And with that, hopefully make it more widely applicable in the research setting.”
Ultimately, Harper hopes this research on the underlying mechanisms of pain will lead to better treatments for those suffering with fibromyalgia and other chronic pain conditions.