Investigating Pain-Related Avoidance Behavior using a Robotic Arm-Reaching Paradigm

Avoidance behavior is a key contributor to the transition from acute pain to chronic pain disability. Yet, there has been a lack of ecologically valid ...

KU Leuven

Ample empirical evidence endorses the role of associative learning in pain-related fear acquisition. Nevertheless, research typically focused on self-reported and psychophysiological measures of fear. Avoidance, which is overt behavior preventing the occurrence of an aversive (painful) stimulus, has been largely neglected so far. Therefore, we aimed to fill this gap and developed an operant conditioning procedure for pain-related avoidance behavior. Participants moved their arm to a target location using the HapticMaster (FCS Robotics; Moog Inc, East Aurora, New York), a 3 degrees-of-freedom, force-controlled robotic arm. Three movement trajectories led to the target location. If participants in the Experimental Group took the shortest/easiest trajectory, they always received a painful stimulus (T1 = 100% reinforcement; no resistance). If they deviated from this trajectory, the painful stimulus could be partly or totally prevented (T2 = 50% reinforcement; T3 = 0% reinforcement), but more effort was needed (T2 = moderate resistance and deviation; T3 = strongest resistance and largest deviation). The Yoked Group received the same reinforcement schedule irrespective of their own behavior. During the subsequent extinction phase, no painful stimuli were delivered. Self-reported pain-expectancy and pain-related fear were assessed, and avoidance behavior was operationalized as the maximal distance from the shortest trajectory. During acquisition, the Experimental Group reported more pain-related fear and pain-expectancy to T1 vs T2 vs T3 and deviated more from the shortest trajectory than the Yoked Group. During subsequent extinction, avoidance behavior, self-reported fear, and pain-expectancy decreased significantly, but conditioned differences persisted despite the absence of painful stimuli. To conclude, this operant learning task might provide a valid paradigm to study pain-related avoidance behavior in future studies. 

Acquisition and extinction of operant pain-related avoidance behavior using a 3 degrees-of-freedom robotic arm.

In two experiments, using an online conditioned suppression task, we investigated the possibility of reinstatement of extinguished feature-target compound presentations after sequential feature-positive discrimination training in humans. Furthermore, given a hierarchical account of Pavlovian modulation (e.g., Bonardi, 1998; Bonardi and Jennings, 2009), we predicted A-US reinstatement to be stronger than US-only reinstatement. In Experiment 1, participants learned a sequential feature-positive discrimination (X→A|A), which was subsequently extinguished (X→A). During the following reinstatement phase, group US-only received US-only presentations (not signalled), group A-US received A-US presentations, and the Control group received exposure to the context, but no CSs or USs, for an equal amount of time. Reinstatement of differential X→A/A responding was observed in the US-only group but not in the Control or A-US groups. Although differential X→A/A responding was not significant in group A-US, responding to the X→A compound was significantly stronger compared to that in group US-only. Hence, it could be the case the group A-US showed stronger reinstatement, but that differential responding was abolished due to excitation gained by A. Experiment 2 was set up to circumvent the acquired excitation of A by testing transfer of the feature after A-US reinstatement to a different target, B. Participants acquired two discriminations, X→A/A and Y→B/B, of which X→A was then extinguished. Subsequently, group A-US received reinforced presentations of A during a reinstatement phase while group Control received exposure to the context. Final testing of the novel X→B compound was hypothesized to show higher responding in group A-US than in group Control, but findings of this approach were limited due to acquired equivalence and/or perceptual factors causing a secondary extinction effect. We conclude to have obtained clear evidence in favour of reinstatement of differential responding after human Feature-Positive discrimination training and subsequent compound extinction, but no evidence in favour of A-US presentations being a stronger trigger for reinstatement than are US-only presentations.

Reinstatement after human feature-positive discrimination learning.

Slow deep breathing (SDB) is commonly employed in the management of pain, but the underlying mechanisms remain equivocal. This study sought to investigate effects of instructed breathing patterns on experimental heat pain and to explore possible mechanisms of action. In a within-subject experimental design, healthy volunteers (n = 48) performed 4 breathing patterns: 1) unpaced breathing, 2) paced breathing (PB) at the participant's spontaneous breathing frequency, 3) SDB at 6 breaths per minute with a high inspiration/expiration ratio (SDB-H), and 4) SDB at 6 breaths per minute with a low inspiration/expiration ratio (SDB-L). During presentation of each breathing pattern, participants received painful heat stimuli of 3 different temperatures and rated each stimulus on pain intensity. Respiration, heart rate, and blood pressure were recorded. Compared to unpaced breathing, participants reported less intense pain during each of the 3 instructed breathing patterns. Among the instructed breathing patterns, pain did not differ between PB and SDB-H, and SDB-L attenuated pain more than the PB and SDB-H patterns. The latter effect was paralleled by greater blood pressure variability and baroreflex effectiveness index during SDB-L. Cardiovascular changes did not mediate the observed effects of breathing patterns on pain. PERSPECTIVES: SDB is more efficacious to attenuate pain when breathing is paced at a slow rhythm with an expiration that is long relative to inspiration, but the underlying mechanisms remain to be elucidated.

Can Slow Deep Breathing Reduce Pain? An Experimental Study Exploring Mechanisms.

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.

Mathijs Franssen

Research Group Health Psychology

KU Leuven

Investigating Pain-Related Avoidance Behavior using a Robotic Arm-Reaching Paradigm

Mathijs Franssen

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Research Group Health Psychology

KU Leuven

Investigating Pain-Related Avoidance Behavior using a Robotic Arm-Reaching Paradigm

Research Group Health Psychology