The fear-avoidance model of pain

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