The effect of experimentally induced anxiety on the experience of pressure pain.

Two theories about the relationship between anxiety and pain were compared: (1) the attribution theory that relevant but not irrelevant anxiety intensifies pain, and (2) the perceptual disruption theory that all anxiety influences pain. Three types of instructions were presented to randomly selected groups of male university students immediately before nociception: (1) a standard set of instructions, (2) the standard instructions plus a pain warning (relevant anxiety condition), and (3) the standard instructions plus a warning about a stressful interview (irrelevant anxiety condition). Pain and stress intensity ratings, heart rate, frontalis electromyographic activity, and facial expressions were recorded continuously, and pain threshold and pain tolerance were recorded once. The anxiety-evoking effects of the instructions were confirmed by analyses of the stress measures obtained during a waiting period. The results indicated that both relevant and irrelevant anxiety-evoking instructions increased pain ratings, stress intensity ratings, and heart rate compared to standard control instructions when painful pressure was applied to the skin. In addition, the relevant but not the irrelevant anxiety instructions increased electromyographic activity and facial grimaces during nociception. However, tolerance, threshold, and post-experimental ratings did not differ among groups. These results are interpreted as supporting the perceptual disruption theory.