Generalization of instrumentally acquired pain-related avoidance to novel but similar movements using a robotic arm-reaching paradigm

Abstract

Avoidance is considered a key contributor to the development and maintenance of chronic pain disability, likely through its excessive generalization. This study investigated whether acquired avoidance behavior generalizes to novel but similar movements. Using a robotic arm, participants moved their arm from a starting to a target location via one of three possible movement trajectories. For the Experimental Group, the shortest, easiest trajectory was always paired with pain (T1 = 100% reinforcement/no resistance and deviation). Pain could be partly or completely avoided by choosing increasingly effortful movements (T2 = 50% reinforcement, moderate resistance/deviation; T3 = 0% reinforcement, strongest resistance/largest deviation). A Yoked Group received the same number of painful stimuli irrespective of their own behavior. Outcomes were self-reported fear of movement-related pain, pain-expectancy, avoidance behavior, (maximal deviation from the shortest trajectory), and trajectory choice behavior. We tested generalization to three novel trajectories (G1-3) positioned between the acquisition trajectories. Whereas acquired fear of movement-related pain and pain-expectancy generalized in the Experimental Group, avoidance behavior did not, suggesting that threat beliefs and high-cost avoidance may not be directly related. The lack of avoidance generalization may be due to a perceived context-switch in the configurations of the acquisition and the generalization phases.

When Do We Not Face Our Fears? Investigating the Boundary Conditions of Costly Pain-Related Avoidance Generalization

“…Instrumental responses may become directly associated with the learning context 23 , leading to diminished responding when the context is changed 1 . How generalization was operationalized (absence of T1-3 and appearance of G1-3) in Glogan et al 17 may have been experienced by participants as a context-switch 2 , stimulating exploration of the novel trajectories similar to the previously pain-associated ones (G1 and G2), resulting in participants quickly learning that these novel generalization movements were not paired with the electrical stimulus. Therefore, the goal of Experiment 1 was to reduce visual context changes by presenting all trajectory arches simultaneously (fig.…”

“…When trajectories were available, their corresponding arches were colored black, and when they were unavailable, their arches were colored grey. Therefore the acquisition phase was similar to that of Glogan et al 17 , (contingencies: T1 = 100% punishment, T2 = 50% punishment, T3 = 0% punishment) except that all six movement trajectories were presented simultaneously. The acquisition phase consisted of two blocks of 12 trials.…”

“…Both experiments used variations of the same basic paradigm as Glogan et al 17 . On each trial, participants were required to move from a start location to a target location by operating the HM with their right (dominant) hand (see fig.…”

“…During a subsequent generalization test, three novel, similar movements (generalization trajectories) were tested in the absence of the acquisition trajectories and pain. Pain-expectancy and painrelated fear generalized to the novel movements, but avoidance did not 17 , sparking the question under which conditions costly avoidance generalizes.…”

“…There are several plausible explanations for this dissociation 17 . First, the way in which generalization was operationalized (absence of acquisition trajectories and appearance of generalization trajectories) may have been experienced as a context-switch, generating doubt about the acquisition movement-pain contingencies still holding during the generalization phase 1, 2 , and thus uncertainty about the continued need for effort.…”