Approach and avoidance beyond verbal measures: A quantitative meta-analysis of human conditioned place preference studies.

Adaptive approach and avoidance in responses to reward and threat are fundamental to prevent harm and to ensure well-being. In contrast, maladaptive approach or avoidance behavior likely contributes to anxiety or substance abuse disorders, respectively. Therefore, there is a need to assess such behavior in humans objectively. Conditioned place preference (CPP) is a well-established animal paradigm investigating approach-avoidance mechanisms, i.e., context-associated appetitive/aversive effects of unconditioned stimuli. Recently, the retranslation of this paradigm for human research started. This meta-analysis provides the first systematic overview of this developing field. A total of 17 studies published before June 2020 fulfil our inclusion criteria: (1) Usage of a rewarding agent, (2) implementation of either virtual or real environments, (3) human subjects, and (4) report of standardized outcome measures. These studies were evaluated and analyzed following the DIAD model and the PRISMA guidelines, respectively, and specific subanalyses were preformed to identify modulating factors of CPP effects (e.g., Virtual Reality applications, biased/unbiased). Overall, a significant medium effect size for the behavioral measure of dwell time (g =.62, p < .001, 95%-CI =.43-.81) and a significant small effect size for verbal self-ratings (g =.33, p < .001, 95%-CI =.04-.63) were observed, although across-study results were characterized by substantial heterogeneity (l2 > 65%). These results indicate great potential for CPP to study approach-avoidance behavior in humans, directly in analogy to animal studies. We provide guidelines for future CPP research to improve comparability of studies and to facilitate new insights into anxiety disorders and drug abuse.