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

Summary

Avoidance is central to chronic pain disability, yet adequate paradigms for examining pain-related avoidance are lacking. Therefore, we developed a paradigm that allows investigating how pain-related avoidance behavior is learned (acquisition), spreads to other stimuli (generalization), can be mitigated (extinction), and how it may subsequently re-emerge (spontaneous recovery).

Abstract

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 paradigms to experimentally investigate pain-related avoidance. To fill this gap, we developed a paradigm (the robotic arm-reaching paradigm) to investigate the mechanisms underlying the development of pain-related avoidance behavior. Existing avoidance paradigms (mostly in the context of anxiety research) have often operationalized avoidance as an experimenter-instructed, low-cost response, superimposed on stimuli associated with threat during a Pavlovian fear conditioning procedure. In contrast, the current method offers increased ecological validity in terms of instrumental learning (acquisition) of avoidance, and by adding a cost to the avoidance response. In the paradigm, participants perform arm-reaching movements from a starting point to a target using a robotic arm, and freely choose between three different movement trajectories to do so. The movement trajectories differ in probability of being paired with a painful electrocutaneous stimulus, and in required effort in terms of deviation and resistance. Specifically, the painful stimulus can be (partly) avoided at the cost of performing movements requiring increased effort. Avoidance behavior is operationalized as the maximal deviation from the shortest trajectory on each trial. In addition to explaining how the new paradigm can help understand the acquisition of avoidance, we describe adaptations of the robotic arm-reaching paradigm for (1) examining the spread of avoidance to other stimuli (generalization), (2) modeling clinical treatment in the lab (extinction of avoidance using response prevention), as well as (3) modeling relapse, and return of avoidance following extinction (spontaneous recovery). Given the increased ecological validity, and numerous possibilities for extensions and/or adaptations, the robotic arm-reaching paradigm offers a promising tool to facilitate the investigation of avoidance behavior and to further our understanding of its underlying processes.

Introduction

Avoidance is an adaptive response to pain signaling bodily threat. Yet, when pain becomes chronic, pain and pain-related avoidance lose their adaptive purpose. In line with this, the fear-avoidance model of chronic pain^{1,2,3,4,5,6,7,8} posits that erroneous interpretations of pain as catastrophic, trigger increases in fear of pain, which motivate avoidance behavior. Excessive avoidance can lead to the dev....

Protocol

The protocols presented here meet the requirements of the Social and Societal Ethics committee of the KU Leuven (registration number: S-56505), and the Ethics Review Committee Psychology and Neuroscience of Maastricht University (registration numbers: 185_09_11_2017_S1 and 185_09_11_2017_S2_A1).

1. Preparing the laboratory for a test session

1. Before the test session: Send the participant an e-mail informing him/her about the delivery of pain stimuli, of the general outline of the ex.......

Discussion

Given the key role of avoidance in chronic pain disability^1,2,3,4,5, and the limitations faced by traditional avoidance paradigms¹⁹, there is a need for methods to investigate (pain-related) avoidance behavior. The robotic arm-reaching paradigm presented here addresses a number of these limitations. We have employed the paradigm in a se.......

Materials

Name	Company	Catalog Number	Comments
1 computer and computer screen	Intel Corporation	64-bit Intel Core	Running the experimental script
40 inch LCD screen	Samsung Group		Presenting the experimental script
Blender 2.79	Blender Foundation		3D graphics software for programming the graphics of the experiment
C#			Programming language used to program the experimental task
Conductive gel	Reckitt Benckiser	K-Y Gel	Facilitates conduction from the skin to the stimulation electrodes
Constant current stimulator	Digitimer Ltd	DS7A	Generates electrical stimulation
HapticMaster	Motekforce Link		Robotic arm
Matlab	MathWorks		For writing scripts for participant randomization schedule, and for extracting maximum deviation from shortest trajectory per trial
Qualtrics	Qualtrics		Web survey tool for psychological questionnaires
Rstudio	Rstudio Inc.		Statistical analyses
Sekusept Plus	Ecolab		Disinfectant solution for cleaning medical instruments
Stimulation electrodes	Digitimer Ltd	Bar stimulating electrode	Two reusable stainless steel disk electrodes; 8mm diameter with 30mm spacing
Tablet	AsusTek Computer Inc.	ASUS ZenPad 8.0	For providing responses to psychological trait questinnaires
Triple foot switch	Scythe	USB-3FS-2	For providing self-report measures on VAS scale
Unity 2017	Unity Technologies		Cross-platform game engine for writing the experimental script including presentations of electrocutaneous stimuli