title: Classical Conditioning Differences Associated With Chronic Pain: A Systematic Review.
abstract: Prominent clinical models of chronic pain propose a fundamental role of classical conditioning in the development of pain-related disability. If classical conditioning is key to this process, then people with chronic pain may show a different response to pain-related conditioned stimuli than healthy control subjects. We set out to determine whether this is the case by undertaking a comprehensive and systematic review of the literature. To identify studies comparing classical conditioning between people with chronic pain and healthy control subjects, the databases MEDLINE, PsychINFO, PsychARTICLES, Scopus, and CINAHL were searched using key words and medical subject headings consistent with 'classical conditioning' and 'pain.' Articles were included when: 1) pain-free control and chronic pain groups were included, and 2) a differential classical conditioning design was used. The systematic search revealed 7 studies investigating differences in classical conditioning between people with chronic pain and healthy control participants. The included studies involved a total of 129 people with chronic pain (fibromyalgia syndrome, spinal pain, hand pain, irritable bowel syndrome), and 104 healthy control participants. Outcomes included indices of pain-related conditioning such as unconditioned stimulus (US) expectancy and contingency awareness, self-report and physiological measures of pain-related fear, evaluative judgements of conditioned stimulus pleasantness, and muscular and cortical responses. Because of variability in outcomes, meta-analyses included a maximum of 4 studies. People with chronic pain tended to show reduced differential learning and flatter generalization gradients with respect to US expectancy and fear-potentiated eyeblink startle responses. Some studies showed a propensity for greater muscular responses and perceptions of unpleasantness in response to pain-associated cues, relative to control cues.
  
  
  
  The review revealed preliminary evidence that people with chronic pain may exhibit less differential US expectancy and fear learning. This characteristic may contribute to widespread fear-avoidance behavior. The assumption that altered classical conditioning may be a predisposing or maintaining factor for chronic pain remains to be verified.
authors.affiliation: Body in Mind Research Group, Sansom Institute for Health Research, University of South Australia, Adelaide, Australia; Recover Injury Research Centre, Menzies Health Institute Queensland, Griffith University, Gold Coast, Australia. Electronic address: d.harvie@griffith.edu.au.
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Harvie
authors.affiliation: Body in Mind Research Group, Sansom Institute for Health Research, University of South Australia, Adelaide, Australia; Neuroscience Research Australia, Sydney, Australia.
authors.forename: G Lorimer
authors.initials: GL
authors.lastname: Moseley
authors.affiliation: Body in Mind Research Group, Sansom Institute for Health Research, University of South Australia, Adelaide, Australia.
authors.forename: Susan L
authors.initials: SL
authors.lastname: Hillier
authors.affiliation: Research Group on Health Psychology, University of Leuven, Leuven, Belgium; Center for Excellence on Generalization Research in Health and Psychopathology, University of Leuven, Leuven, Belgium.
authors.forename: Ann
authors.initials: A
authors.lastname: Meulders
mesh_terms: D000818:Animals; D059350:Chronic Pain / Q000150:complications* / Q000523:psychology; D003214:Conditioning, Classical / Q000502:physiology*; D006233:Persons with Disabilities; D006801:Humans; D007859:Learning Disabilities / Q000209:etiology*
keywords: Classical conditioning; associative learning; chronic pain; learning deficits