Dissociation Between Individual Differences in Self-Reported Pain Intensity and Underlying Brain Activation

Abstract

Pain is a uniquely individual experience. Previous studies have highlighted changes in brain activation and morphology associated with inter- and intra-individual pain perception. In this study we sought to characterize brain mechanisms associated with individual differences in pain in a large sample of healthy participants (N = 101). Pain ratings varied widely across individuals. Moreover, individuals reported changes in pain evoked by small differences in stimulus intensity in a manner congruent with their pain sensitivity, further supporting the utility of subjective reporting as a measure of the true individual experience. However, brain activation related to inter-individual differences in pain was not detected, despite clear sensitivity of the BOLD signal to small differences in noxious stimulus intensities within individuals. These findings raise questions about the utility of fMRI as an objective measure to infer reported pain intensity.

Not all noise-reduction methods for fMRI preprocessing are created equal

“…143 healthy individuals (age range: 14 to 44 years old) were enrolled in a neuroimaging study investigating the individual experience of pain. Data from 34 of these participants (Table 1; age: 28 ± 6.1, mean ± SD), which were not used in any prior analyses (Hoeppli et al, 2020), were used to train an automated classifier FSL FIX (FMRIB’s ICA-based Xnoiseifier, FSL, Oxford, UK) (Griffanti et al, 2014; Salimi-Khorshidi et al, 2014) that was used to denoise the fMRI data. 4 of these 34 participants had subtle incidental findings reported by a radiologist, that due to their nature and localization should not affect the training of the FIX classifier.…”

“…The goal of the QST session was to familiarize participants with the stimuli and rating scale used in the MRI session. This session will not be further discussed in this manuscript, but a detailed description of this session can be found elsewhere (Hoeppli et al, 2020). The MRI session lasted approximately 90 minutes.…”

“…After each stimulus, participants were asked to rate their pain intensity and unpleasantness sensations on two computerized visual analog scales. A complete description of the scale can be found in Hoeppli et al (Hoeppli et al, 2020). Only the heat and auditory fMRI series will be detailed below; since analyses reported in this manuscript were performed on these stimulus modalities only.…”

“…An in-depth description of the cold stimulus modality is available in Hoeppli & al. (Hoeppli et al, 2020). We chose to focus on the heat pain modality, as it is one of the stimulus modalities most frequently used to experimentally induce pain and is associated with a physiological response that might impact the MRI response.…”

“…Only the heat and auditory fMRI series will be detailed below; since analyses reported in this manuscript were performed on these stimulus modalities only. An in-depth description of the cold stimulus modality is available in Hoeppli & al. (Hoeppli et al, 2020).…”