1. Fear and avoidance of pain
The large individual variations in response to a similar nociceptive stimulus and the development of persistent pain after an acute pain episode have puzzled researchers and clinicians alike. Pain is a biologically relevant and vital signal of bodily threat, urging protective behaviors, which include increased arousal, prioritization of attention to the sources of pain, instant withdrawal, facial expression, and avoidance. The Fear-Avoidance model (Figure 1) has been introduced as a theoretical model to guide pain research and management, describing the cascade of events after pain that is perceived as threatening.8,12
2. Acquisition and generalization
Fear is the anticipatory emotional response to imminent threat, and adaptive learning takes place rapidly, either through direct experience,9 observation,5 or verbal instructions.1,4 Initial neutral cues (conditioned stimuli, CS) causally or functionally associated with pain may capture the attention and elicit protective fear responses (conditioned responses such as avoidance), that may be different from unconditioned responses (UR) such as the immediate escape from the unconditioned pain stimulus (US) (see panels 1 and 2).11 Learning typically occurs with interoceptive or proprioceptive CSs. Chronic pain may develop when pain-related fear and avoidance persists despite healing, or when protective responses generalize to novel situations (GS) that share features with the CS (see panel 3). Avoidance behavior is overt or covert behavior that prevents or postpones the encounter with an aversive stimulus, and is a key element in the FA model. Avoidance behavior once acquired is notoriously persistent, and usually maintains pain-related fear. Avoidance usually implies activity restrictions, interference with valued life activities, and negative affect. Avoidance can be used as a source of information to derive danger, for example: “I am avoiding, therefore there must be danger.” The relief that the expected threat did not occur may reinforce avoidance behaviors, and hence maintaining it.14
3. Pain in context
Pain-related fear is not always associated with avoidance behavior. The expression of pain-related fear and avoidance behavior is dependent on context. The goal to avoid pain is only one to be pursued in an environment with concomitant, often competing goals.3 Fear-related protective behaviors are inhibited when the value of another life goal outweighs the value of pain and is given priority.2 Negative affect and harm representations may increase the engagement in pain control, whereas positive affect6 and optimism may foster the priority to valued life goals.7
4. Extinction of pain-related fear
Inhibitory responses can be learned when avoidance behavior is omitted, and the individual is exposed to the stimuli and situations that were previously avoided (see panel 4). In such exposure treatments, new nonthreat associations with the CSs are formed, and subsequently may generalize across time and contexts.7 In contrast to its acquisition, the extinction of pain-related fear is fragile, context-dependent, and it does not easily generalize to novel situations. Exposure-based treatments have been shown to be effective in various pain syndromes, both in adults and youngsters.10,13
. Bennett MP, Meulders A, Baeyens F, Vlaeyen JWS. Words putting pain in motion: the generalization of pain-related fear within an artifi cial stimulus category. Front Psychol 2015;6:520.
. Claes N, Crombez G, Vlaeyen JW. Pain-avoidance versus reward-seeking: an experimental investigation. PAIN 2015;156:1449–57.
. Crombez G, Eccleston C, Van Damme S, Vlaeyen JW, Karoly P. Fear-avoidance model of chronic pain: the next generation. Clin J Pain 2012;28:475–83.
. Crombez G, Kissi A. The future is bright: On the behavioural consequences of rule-following. In: Main C, Keefe F, Jensen M, Vlaeyen JW, Vowles K, editors. Fordyce’s Behavioral Methods for chronic Pain and Illness republished with invited commentaries: IASP and Wolters-Kluwer, 2014.
. Goubert L, Vlaeyen JW, Crombez G, Craig KD. Learning about pain from others: an observational learning account. J Pain 2011;12:167–74.
. Goubert L, Crombez G, Van Damme S. The role of neuroticism, pain catastrophizing and pain-related fear in vigilance to pain: a structural equations approach. PAIN 2004;107:234–41.
. Hanssen MM, Peters ML, Vlaeyen JW, Meevissen YM, Vancleef LM. Optimism lowers pain: evidence of the causal status and underlying mechanisms. PAIN 2013;154:53–8.
. Lethem J, Slade PD, Troup JD, Bentley G. Outline of a Fear-Avoidance Model of exaggerated pain perception–I. Behav Res Ther 1983;21:401–8.
. Meulders A, Vlaeyen JW. The acquisition and generalization of cued and contextual pain-related fear: an experimental study using a voluntary movement paradigm. PAIN 2013;154:272–82.
. Simons LE. Fear of pain in children and adolescents with neuropathic pain and complex regional pain syndrome. PAIN 2016;157(Suppl 1):S90–97.
. Vlaeyen JW. Learning to predict and control harmful events: chronic pain and conditioning. PAIN 2015;156(suppl 1):S86–93.
. Vlaeyen JW, Linton SJ. Fear-avoidance model of chronic musculoskeletal pain: 12 years on. PAIN 2012;153:1144–7.
. Vlaeyen JW, Morley S, Linton S, Boersma K, De Jong J. Pain-related fear: exposure-based treatment for chronic pain. Seattle: IASP Press, 2012.
. Volders S, Boddez Y, De Peuter S, Meulders A, Vlaeyen JW. Avoidance behavior in chronic pain research: a cold case revisited. Behav Res Ther 2015;64:31–7.