Emotional modulation of pain and spinal nociception in fibromyalgia

Abstract

Fibromyalgia (FM) is characterized by widespread pain, as well as affective disturbance (eg, depression). Given that emotional processes are known to modulate pain, a disruption of emotion and emotional modulation of pain and nociception may contribute to FM. The present study used a well-validated affective picture-viewing paradigm to study emotional processing and emotional modulation of pain and spinal nociception. Participants were 18 individuals with FM, 18 individuals with rheumatoid arthritis (RA), and 19 healthy pain-free controls (HC). Mutilation, neutral, and erotic pictures were presented in 4 blocks; 2 blocks assessed only physiological-emotional reactions (ie, pleasure/arousal ratings, corrugator electromyography, startle modulation, skin conductance) in the absence of pain, and 2 blocks assessed emotional reactivity and emotional modulation of pain and the nociceptive flexion reflex (NFR, a physiological measure of spinal nociception) evoked by suprathreshold electric stimulations over the sural nerve. In general, mutilation pictures elicited displeasure, corrugator activity, subjective arousal, and sympathetic activation, whereas erotic pictures elicited pleasure, subjective arousal, and sympathetic activation. However, FM was associated with deficits in appetitive activation (eg, reduced pleasure/arousal to erotica). Moreover, emotional modulation of pain was observed in HC and RA, but not FM, even though all 3 groups evidenced modulation of NFR. Additionally, NFR thresholds were not lower in the FM group, indicating a lack of spinal sensitization. Together, these results suggest that FM is associated with a disruption of supraspinal processes associated with positive affect and emotional modulation of pain, but not brain-to-spinal cord circuitry that modulates spinal nociceptive processes.

Figure 1

Experimental procedures.

Figure 2

Emotional valence (valence ratings, corrugator EMG, startle) and arousal (arousal ratings, skin conductance response [SCR]) reactions to pictures in the absence of pain testing. Emotional modulation of noise ratings is depicted in the bottom right graph. HC=pain-free healthy controls, RA= participants with rheumatoid arthritis, FM=participants with fibromyalgia. *p<.05

Figure 3

Group differences in nociceptive flexion reflex (NFR) threshold. Filled circles depict raw data for each group, whereas unfilled boxes represent group means. NFR threshold was significantly higher in participants with fibromyalgia (FM) compared to pain-free healthy controls (HC) and participants with rheumatoid arthritis (RA) (ps < .05). If those participants with FM who reached the 50 mA max were removed (n=5), there were no group differences. Together, these data indicate that the FM group does not have tonic spinal sensitization.

Figure 4

Emotional valence (valence ratings, corrugator EMG) and arousal (arousal ratings, skin conductance response [SCR]) reactions to pictures during pain testing. HC=pain-free healthy controls, RA= participants with rheumatoid arthritis, FM=participants with fibromyalgia. *p<.05

Figure 5

Emotional modulation of pain (left graph) and nociceptive flexion reflex (NFR; right graph) in healthy controls (HC), participants with rheumatoid arthritis (RA), and participants with fibromyalgia (FM). Emotional modulation of pain was evident in HC and RA, but not FM. By contrast, all groups demonstrated emotional modulation of spinal nociception (NFR).