(648): Conditioned fear-induced pain modulation in humans: The influence of preparedness

Abstract

Research suggests conditioned fear modulates pain. However, it is unknown whether any variables moderate this relationship. Preparedness theory predicts that some conditioned stimuli (CS) are more readily associated with an unconditioned stimulus (US) and lead to more rapid development of the conditioned fear response. Indeed, pictures depicting facial expressions of fear are more readily associated with an aversive shock US and lead to greater conditioned responses than happy expressions. Therefore, different types of CSs may moderate the influence of conditioned fear on pain. The present study used a differential fear conditioning procedure to examine the influence of conditioned fear on pain threshold (latency of finger withdrawal to radiant heat). Facial expressions (happy vs. fear) served as the CSs and aversive electric stimulation of the sural nerve as the US. Forty-one participants were randomly assigned to have either a fear or happy expression as the CS+ (stimulus paired with shock). The other facial expression served as the CS− (stimulus unpaired with shock). During the acquisition phase, each CS was presented in pseudorandom order, and the CS+ was always paired with shock. During the extinction phase, shock was no longer presented and pain threshold was tested during each CS. Psychophysiological and self-report measures of emotion were used to verify participants’ reactions to CSs and results suggest that fear was effectively conditioned. However, only those people for whom the fear expression served as the CS+ evidenced any pain modulation (p=.01), with lower pain thresholds (hyperalgesia) during the CS+ relative to the CS−. People for whom a happy expression served as the CS+ did not have a significant difference in pain thresholds during the CS+ versus the CS− (p>.05). In sum, these data suggest that conditioned fear-induced pain modulation is moderated by the type of conditioned stimuli used.