Pain distribution can be determined by classical conditioning

Chronic widespread pain (CWP) - as in many other clinical presentations - manifests in ongoing pain without identifiable structural cause, with pain that spreads over multiple body areas. The development and maintenance of symptoms may involve learning mechanisms. Ninety-four healthy volunteers participated in this study and were randomly distributed to 4 groups. In the classical conditioning combined with the verbal suggestion group, US- (small pain distribution) and US+ (large pain distribution) were paired with visual stimuli (CS+ and CS-), and participants were told about this association. In the verbal suggestion group, the conditioning was not performed, whereas in the classical conditioning-only group, learning was not combined with suggestion. In the control group, conditioning and suggestion did not take place. Ratings of perceived pain distribution were collected after each trial and ratings of pain intensity after each block of trials. During the testing phase, participants were exposed to electrocutaneous stimuli corresponding to only the small (US-) pain distribution. The results showed significant differences between CS+ and CS- pain distribution ratings across the experimental groups: conditioning + verbal suggestion (P < 0.01), conditioning-only group (P < 0.05), and verbal suggestion-only group (P < 0.05), but not in the control group (P > 0.05). Furthermore, significant differences in the perceived pain distribution were found between the control group and all experimental groups. This result supports our main hypothesis that the perceived pain distribution can be influenced by classical conditioning as well as verbal suggestion, although the effect is stronger when both are combined.