Classical conditioning differences associated with chronic pain: a systematic review

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 (CS) than healthy controls. 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 controls, the databases MEDLINE, PsychINFO, PsychARTICLES, Scopus, CINAHL, were searched using key words and MESH headings consistent with ‘classical conditioning’ AND ‘pain’. Articles were included when a) pain-free control and chronic pain groups were included, and b) a differential classical conditioning design was used. The systematic search revealed seven studies investigating differences in classical conditioning between people with chronic pain and healthy controls. The included studies involved a total of 129 people with chronic pain (Fibromyalgia syndrome, Spinal pain, Hand pain, Irritable bowel syndrome), and 104 healthy controls. 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 judgments of conditioned stimulus (CS) pleasantness, and muscular and cortical responses. Due to variability in outcomes, meta-analyses included a maximum of four studies. People with chronic pain tended to show reduced differential learning and flatter generalisation gradients with respect to US-expectancy and fear-potentiated eyeblink startle responses. Some studies demonstrated a propensity for greater muscular responses and perceptions of unpleasantness in response to pain-associated cues, relative to control cues.