1. Functional MRI (fMRI) can reliably discern thermal pain based on a reproducible neurologic signature.
2. The signature was specific for physical pain (vs. social pain) and also reduced in a dose-dependent manner in response to infusion of remifentanil.
Study Rundown: Pain is an unpleasant sensory and emotional experience that is unique to each patient. Most clinical tools to date used to assess pain, such as the Visual Analog Scale, cannot be reliably applied to very young or old, cognitively impaired or minimally conscious patients. For these patients, an imaging-based approach may be a useful method of assessing pain. By examining neurologic signatures to provoked pain on functional MRI (fMRI), this study examined whether these signatures could provide a direct measure of pain and be used to compare the efficacies of certain analgesics.
This study identified the first reliable neurologic signature for thermal pain on functional MRI (fMRI). However, the results cannot be generalized readily to the important population of chronic or neuropathic pain patients, since the pain in this study was only thermal in nature and delivered at predictable intervals to otherwise healthy patients. Future studies will need to examine the reliability of fMRI signatures in the setting of various other types of pain and at different sites on the body.
In-Depth: This study included results from four smaller studies with a total of 114 healthy participants enrolled. All studies involved thermal stimuli in randomized sequences and various intensities to the left forearm. Study 1 examined various areas of the brain that increased in activity (“signatures”) when the stimulus was applied; fMRI was 95% sensitive and 95% specific at distinguishing pain vs. warmth (P<0.001). Study 2 revealed a neurologic signature that was predictive of the stimulus intensity (beta=0.20, t=6.84, P<0.001). Study 3 revealed a stronger neurologic signature to physical pain than when participants were shown a picture of a friend or ex-partner (social pain). Study 4 revealed a signature response that was reduced in parallel to an increase in the remifentanil infusions (t=-2.78 with open infusion, t=-2.77 with hidden infusion; P=0.01); the results did not differ in the open v. hidden-infusion groups.
By Jonathan Liu and Mitalee Patil
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