The project investigates on the role of pain avoidance, comorbidity and stress response for the development of chronic somatic and visceral pain. We, the researchers at University Hospital Mannheim, assume that implicit operant learning of pain sensitization is a central mechanism of the process of pain becoming chronic, which is augmented by fear and by avoidance behaviour. Somatic and psychological comorbidity as well as stress factors are further promoting factors in chronic pain development.