Functional MRI Reveals Emotional Modulation of Pain Processing in the Human Cervical Spinal Cord and Brainstem

Background: Prior research has demonstrated that emotional state can influence pain perception. If a noxious stimulus is coupled with a negative emotional stimulus, the perception of the noxious stimulus will be heightened by the aversive associations of the negative emotional stimulus. In contrast, pain ratings decrease with positive emotional influence. The aim of the current study was to characterize the emotional modulation of pain processing in the spinal cord and brainstem using functional MRI. Methods: Twenty-one healthy, right-handed females, aged 18-30 (M age = 21.5) underwent an fMRI scan of the spinal cord and brainstem while completing a heat pain-rating task. Participants received noxious thermal stimulus to the thenar eminence of the right hand while viewing images of varying emotional contexts (Positive, Neutral, or Negative), and provided ratings of pain Intensity and Unpleasantness. Results: Pain ratings reflected a significant effect for emotional context, with the Negative emotional condition eliciting significantly greater pain Intensity (M = 48.74, SD = 10.60) and Unpleasantness (M = 36.60, SD = 11.92) ratings than the Positive Intensity (M = 44.22, SD = 10.75) and Unpleasantness (M = 29.05, SD = 10.09) ratings (p < 0.01). In addition to replicating the well-established effect for emotional modulation of pain perception, BOLD responses in regions of the spinal cord and brainstem that are known to function in pain processing also exhibited an effect for descending emotional modulation of pain processing. These regions included the ipsilateral, dorsal horn of the T1 spinal cord segment (caudal to the segment corresponding to the stimulated dermatome), as well as regions in the brainstem approximating the dorsal reticular nucleus of the caudal medulla and the parabrachial nuclei of the pons (p < 0.001). Conclusion: These findings provide novel insight into the neural correlates of descending emotional modulation of pain processing. Furthermore, this study highlights key areas of focus for future research to examine potential individual-level differences in emotional modulation of pain neural processing in the spinal cord and brainstem.