Women, but not men, report increasingly more pain during repeated (un)predictable painful electrocutaneous stimulation: Evidence for mediation by fear of pain.

An abundance of animal research suggests that fear inhibits pain whereas anxiety increases it. Human studies on this topic are more scarce, and the existing evidence seems rather inconsistent. Therefore, we aimed to investigate the divergent effects of both negative emotional states-that is, pain-related fear and anxiety on pain sensitivity and unpleasantness. Possible sex-related differences were also under investigation, as well as the potential mediational role of fear of movement-related pain on the differences in pain intensity and unpleasantness between both sexes. We employed a voluntary joystick movement paradigm using movements as conditioned stimuli (CSs) and a painful electrocutaneous stimulus as the unconditioned stimulus. Healthy participants received predictable shocks in one condition and unpredictable shocks in another condition. The former procedure is known to induce fear of movement-related pain to the CS+ movement (movement consistently followed by pain), whereas the latter procedure induces (contextual) pain-related anxiety. Results showed that fear of movement-related pain indeed resulted in decreased pain intensity/unpleasantness ratings, while pain-related anxiety led to increased pain intensity/unpleasantness reports. Further, the anticipated sex difference was modulated by time. That is, women gradually reported more pain/unpleasantness, whereas men do not show such a sensitization effect. Moreover, this sex-specific sensitization is partially mediated by (conditioned) fear of movement-related pain. Women also report increasingly more fear of pain over conditioning blocks, while men do not. These results might be interesting in the light of the overrepresentation of women in a number of clinical pain conditions as well as anxiety disorders.