Avoiding Based on Shades of Gray: Generalization of Pain-Related Avoidance Behavior to Novel Contexts.

Avoidance behavior is protective, yet in the absence of genuine bodily threat, it may become disabling. Therefore, we investigated whether avoidance generalizes to novel safe contexts based on the similarity with the acquisition context. Healthy participants performed arm movements using a robotic arm to reach a target. Three trajectories (T1-3) led to the target. During acquisition, a painful stimulus could be partly/completely prevented by performing more effortful trajectories (ie, longer and more force needed), T2/T3, in the pain-avoidance context (eg, black background); in the yoked context (eg, white background), the same reinforcement schedule was applied irrespective of the chosen trajectories. Generalization of avoidance was tested in 2 novel contexts (eg, shades of gray backgrounds). We assessed self-reported pain-expectancy and pain-related fear for all trajectories, and avoidance behavior (ie, maximal deviation from T1). Results confirm that fear and expectancy ratings reflect the response-outcome contingencies and differential learning selectively generalized to the novel context resembling the original pain-avoidance context. Furthermore, a linear trend in avoidance behavior across contexts emerged, which is indicative of a generalization gradient. Participants avoided more in the context resembling the original pain-avoidance context than in the one resembling the yoked context, but this effect was not statistically significant. PERSPECTIVE: Perspective: We demonstrated acquisition of pain-related avoidance behavior in a within-subjects design, showing modulation of pain-related fear and pain-expectancy by context and providing limited evidence that avoidance selectively generalizes to novel, similar contexts. These results provide insight regarding the underlying mechanisms of the spreading of protective behavior in chronic pain patients.

Once an Avoider Always an Avoider? Return of Pain-Related Avoidance After Extinction With Response Prevention.

In exposure for chronic pain, avoidance is often forbidden (extinction with response prevention; RPE) to prevent misattributions of safety. Although exposure is an effective treatment, relapse is common. Little is known about the underlying mechanisms of return of pain-related avoidance. We hypothesized that pain-related avoidance would recover when becoming available again after RPE and after unexpected pain episodes ("reinstatement"), especially when restricting avoidance during RPE (compared to instructing not to use it). In an operant pain-related avoidance conditioning paradigm, healthy volunteers used a robotic arm to perform various arm reaching movements differing in pain-effort trade-off. During acquisition, participants learned to avoid pain by performing more effortful movements. During RPE they only performed the formerly pain-associated movement under extinction, and were either forbidden (Restricted group) or merely instructed (Instructed group) not to perform other movements. One day later, we tested spontaneous recovery and reinstatement of pain-related fear and avoidance with availability of all movements. Results showed that pain-related fear and avoidance re-emerge after RPE, though not to pretreatment levels. The reinstatement manipulation had no additional effect. No group differences were observed. We discuss findings in the context of learning processes in (chronic) pain disability and relapse prevention in chronic pain treatment. Perspective: Using experimental models of relapse, we investigated the return of pain-related avoidance behavior after extinction with response prevention. Findings are potentially informative for clinicians performing exposure treatment with chronic pain patients.

Illusion-enhanced Virtual Reality Exercise for Neck Pain: A Replicated Single Case Series.

OBJECTIVES: Body illusions have shown promise in treating some chronic pain conditions. We hypothesized that neck exercises performed in virtual reality (VR) with visual feedback of rotation amplified would reduce persistent neck pain. METHODS: In a multiple-baseline replicated single case series, 8 blinded individuals with persistent neck pain completed a 4-phase intervention (initial n=12, 4 dropouts): (1) "baseline"; (2) "VR" during which participants performed rotation exercises in VR with no manipulation of visual feedback; (3) "VR enhanced" during which identical exercises were performed but visual feedback overstated the range of motion being performed; (4) "follow-up." Primary outcomes were twice-daily measures of pain-free range of motion and pain intensity. During the baseline and follow-up phases, measures were taken but no intervention took place. RESULTS: No differences in primary outcomes were found between VR and baseline, VR enhanced and VR, or VR enhanced and follow-up. DISCUSSION: Our hypothesis, that neck exercises performed in VR with visual feedback of rotation amplified, would reduce persistent neck pain was not supported. Possible explanations and future directions are discussed.

Generalization of Pain-Related Fear Using a Left-Right Hand Judgment Conditioning Task.

Recent research suggests that the mere intention to perform a painful movement can elicit pain-related fear. Based on these findings, the present study aimed to determine whether imagining a movement that is associated with pain (CS+) can start to elicit conditioned pain-related fear as well and whether pain-related fear elicited by imagining a painful movement can spread towards novel, similar but distinct imagined movements. We proposed a new experimental paradigm that integrates the left-right hand judgment task (HJT) with a differential fear conditioning procedure. During Acquisition, one hand posture (CS+) was consistently followed by a painful electrocutaneous stimulus (pain-US) and another hand posture (CS-) was not. Participants were instructed to make left-right judgments, which involve mentally rotating their own hand to match the displayed hand postures (i.e., motor imagery). During Generalization, participants were presented with a series of novel hand postures with six grades of perceptual similarity to the CS+ (generalization stimuli; GSs). Finally, during Extinction, the CS+ hand posture was no longer reinforced. The results showed that (1) a painful hand posture triggers fear and increased US-expectancy as compared to a nonpainful hand posture, (2) this pain-related fear spreads to similar but distinct hand postures following a generalization gradient, and subsequently, (3) it can be successfully reduced during extinction. These effects were apparent in the verbal ratings, but not in the startle measures. Because of the lack of effect in the startle measures, we cannot draw firm conclusions about whether the "imagined movements" (i.e., motor imagery of the hand postures) gained associative strength rather than the hand posture pictures itself. From a clinical perspective, basic research into generalization of pain-related fear triggered by covert CSs such as intentions, imagined movements and movement-related cognitions might further our understanding of how pain and fear avoidance spread and persevere.

The effect of threat information on acquisition, extinction, and reinstatement of experimentally conditioned fear of movement-related pain.

OBJECTIVE: The experiential acquisition of pain-related fear has been demonstrated by pairing a painful electrocutaneous stimulus pain-US; unconditioned pain stimulus) with one movement (CS+; conditioned stimulus) but not with another (CS-). However, it is expected that during acquisition through direct experience, pain-related fear can be intensified or weakened by verbally/visually transmitted information about the pain and its meaning. METHOD: Participants received threatening information (US-inflation), safety information (US-deflation), or no information about the pain-US (US-same). Additionally, we measured return of fear after a reinstatement procedure: two unsignaled pain-USs were presented in the experimental groups, but not in the control groups. RESULTS: We replicated the acquisition and extinction of experimentally induced fear of movement-related pain in healthy subjects both in the verbal reports and the eye-blink startle measures. Two reinstating pain-US presentations led to a differential return of self-reported fear and a nondifferential return of fear in the eye-blink startle responses. Although, we failed to find an effect of verbal/visual information regarding the meaning of the pain-US on the acquisition, extinction, or reinstatement of pain-related fear, we did observe a pain sensitization effect over time suggesting that our threat manipulation induced an increase of perceived threat in all groups. CONCLUSION: The results suggest that our threat manipulation might not have worked or that it was not sensitive enough to yield group-specific effects. We replicated acquisition, extinction, and return of experimentally conditioned fear of movement-related pain, but the threat manipulation failed to generate any additional effects.