Transcranial Direct Current Stimulation of the Dorsolateral Prefrontal Cortex Alters Emotional Modulation of Spinal Nociception.

Emotion has a strong modulatory effect on pain perception and spinal nociception. Pleasure inhibits pain and nociception, whereas displeasure facilitates pain and nociception. Dysregulation of this system has been implicated in development and maintenance of chronic pain. The current study sought to examine whether emotional modulation of pain could be altered through the use of transcranial direct current stimulation (tDCS) to enhance (via anodal stimulation) or depress (via cathodal stimulation) cortical excitability in the dorsolateral prefrontal cortex. Thirty-two participants (15 female, 17 male) received anodal, cathodal, and sham tDCS on three separate occasions, followed immediately by testing to examine the impact of pleasant and unpleasant images on pain and nociceptive flexion reflex (NFR) responses to electrocutaneous stimulation. Results indicated that tDCS modulated the effect of image content on NFR, F(2, 2175.06) = 3.20, P= .04, with the expected linear slope following anodal stimulation (ie, pleasant < neutral < unpleasant) but not cathodal stimulation. These findings provide novel evidence that the dorsolateral prefrontal cortex is critical to emotional modulation of spinal nociception. Moreover, the results suggest a physiological basis for a previously identified phenotype associated with risk for chronic pain and thus a potentially new target for chronic pain prevention efforts. PERSPECTIVE: This study demonstrated that reduction of dorsolateral prefrontal cortical excitability by transcranial direct current stimulation attenuates the impact of emotional image viewing on nociceptive reflex activity during painful electrocutaneous stimulation. This result confirms there is cortical involvement in emotional modulation of spinal nociception and opens avenues for future clinical research.

Pain Acceptance Partially Mediates the Relationship Between Perceived Injustice and Pain Outcomes Over 3 Months.

OBJECTIVES: Perceived injustice is a maladaptive cognitive appraisal of pain or injury, characterized by attributions of blame, unfairness, severity of loss, and irreparability of loss. Research suggests that perceived injustice may negatively affect pain outcomes by inhibiting the development of pain-related acceptance. The current study aimed to extend cross-sectional research by testing whether pain acceptance mediates the effects of perceived injustice on pain-related outcomes longitudinally. MATERIALS AND METHODS: Data was analyzed from a prospective study to examine the potential mediating role of pain acceptance on recovery 3 months after an episode of low back pain. Using Mechanical Turk, we recruited participants who experienced an episode of back pain within the preceding 2 weeks, 343 of whom completed measures of perceived injustice, pain acceptance, pain ratings, and quality of life at each of 3 timepoints (recruitment, 1 mo later, and 3 mo later). Path analyses were conducted to examine pain acceptance at 1 month as a potential mediator of the relationship between perceived injustice at recruitment and pain intensity, disability, and depressive symptoms at 3 months. RESULTS: Results indicated that perceived injustice at recruitment was directly related to pain intensity, disability, and depressive symptoms 3 months later, and that pain acceptance partially mediated these relationships. DISCUSSION: Although these findings provide further support for pain acceptance as a buffer for the deleterious effects of perceived injustice, they also highlight that adjunctive mechanisms should be investigated to provide more comprehensive clinical insight.