Unconscious activation of negative emotional memories increases pain unpleasantness.

OBJECTIVE:The influence of unconscious emotional processes on pain remains poorly understood. The present study tested whether cues to forgotten unpleasant images might amplify pain (i.e., in the absence of conscious recall). METHODS:72 healthy female adults (19 to 34 years) performed an adapted Think/No-think paradigm (T/NT) using 72 combinations of neutral face images (cues) paired with 36 neutral & 36 unpleasant images. After completion of the T/NT task, cues associated with forgotten neutral or unpleasant images were identified. Cues to either neutral or unpleasant images from the NT condition were then presented in randomized order while participants received intermediate-level thermal pain stimulation on the left hand. Ratings of both pain intensity and unpleasantness were acquired after each trial. RESULTS:Mean pain unpleasantness ratings were greater during presentation of cues to forgotten negative vs. neutral images (5.52 [SD = 2.06] vs. 5.23 [SD = 2.10]; p = 0.02). This pattern was also present when comparing cues to remembered negative vs. neutral images (5.62 [SD = 1.94] vs. 5.04 [SD = 1.90]; p < .001). Mean pain intensity ratings were higher for cues to negative vs. neutral images when remembered (5.48 [SD = 1.79] vs. 5.00 [SD = 1.69]; p < .001), but not when forgotten (5.27 [SD = 1.96] vs. 5.16 [SD = 1.93]; p = 0.30). CONCLUSIONS:Using an adapted T/NT-Pain paradigm, this study demonstrated that cues to non-recallable (but potentially unconsciously activated) negative emotional memories amplify pain unpleasantness, similar to known effects of conscious negative emotions.