Operant learning of perceptual sensitization and habituation is impaired in fibromyalgia patients with and without irritable bowel syndrome

The important role of operant learning in the development and maintenance of chronic pain is widely recognized. A specific type of reinforcement based on the reduction of painful stimulation when a person's perception changes in the desired direction has been termed intrinsic reinforcement of pain. In the present study, the role of intrinsic operant learning in chronic pain was tested in fibromyalgia (FM) patients with and without comorbid irritable bowel syndrome (IBS) compared with healthy persons. A previously established operant learning task was used to enhance perceptual sensitization or habituation through intrinsic reinforcement. In addition to subjective pain ratings, pain sensitivity was implicitly measured by a behavioral discrimination task. In accordance with the operant learning task, healthy participants learned enhanced perceptual sensitization and habituation, depending on the experimental condition. Whereas healthy persons learned perceptual changes according the experimental protocol, both patient groups failed to show normal operant perceptual learning: FM patients without IBS demonstrated sensitization learning comparable to that in healthy persons, but unexpectedly these patients learned even more pronounced sensitization in the habituation learning condition, contradicting the experimental protocol; FM patients with IBS demonstrated neither learning of enhanced sensitization nor enhanced habituation; no signs of differential operant learning were observable. Thus, operant perceptual learning was impaired in FM patients; whether learning of both enhanced perceptual sensitization and habituation was impaired depended on the presence of comorbid IBS and could not be explained by other clinical characteristics of the patients such as pain threshold, duration of pain, depressive symptoms, or anxiety.