Your Pain is Showing: Objective Assessment of the Pain Experience

The experience of pain is a subjective one: one person’s pain from an injury could be assessed and reported completely differently than another person’s similar insult (Koyama et al., 2005). These differences in pain reporting could be based on many factors including personal experience and varied expectations. One’s experience of pain consists of an elaborate neuronal system of sensation signaling and is a complicated emotional experience at the same time.

Methods such as the McGill Pain Questionnaire have been in use for decades to help doctors achieve a sensitive quantification of pain levels in their patients based on descriptive reporting (Melzack 1975). Still, a need exists in many instances for an even more objective measure.

Recent studies from the University of Colorado focus on functional imaging of the brain itself, both during application of noxious heat and during application of pleasant warm stimuli (Wager et al., 2013). The authors used functional magnetic resonance imaging (fMRI) to measure brain activity during acute thermal pain in hopes of finding a way to directly measure pain intensity.

The authors report a “neurologic signature” of brain regions that are consistently activated in proportion to a noxious heat stimulus. The regions incorporated in the neurologic signature include the periaqueductal grey, thalamus, posterior and anterior insulae, the secondary somatosensory cortex, the anterior cingulate cortex, among others. This neurologic signature was not activated when subjects were given a non-noxious warm stimulus, and was not affected by anticipation of pain or pain recall. The noxious stimulus was application of a hot plate on the subject’s arm at 49 degrees C and the non-noxious stimulus was application of a hot plate on the arm at 39 degrees C. Interestingly, an analgesic response to the opioid remifentanil was demonstrated by a decreased “signature response” under infusion of the drug with administration of noxious stimulus.

This means that from analyzing the patterns subjects’ brain activity alone, researchers could distinguish which subjects received the thermal pain stimulus and which received analgesic.

This kind of work may be important in assisting populations with trouble communicating their pain, such as those suffering from neurodegenerative disorders like Alzheimer’s disease, minimally conscious patients, or the very old.

What do you think?

Would other types of pain create a neurologic signature?

Could this be important for those suffering chronic pain?

Further Reading:

Koyama T, McHaffie JG, Laurienti PJ, Coghill RC. The subjective experience of pain: where expectations become reality. (2005). Proc Natl Acad Sci U S A. Sep 6;102(36):12950-5.

Melzack R. The McGill Pain Questionnaire: major properties and scoring methods. (1975). Pain. Sep;1(3):277-99.

Wager TD, Atlas LY, Lindquist MA, Roy M, Woo CW, Kross E. An fMRI-based neurologic signature of physical pain. (2013). N Engl J Med. Apr 11;368(15):1388-97.