Once an Optimist, Always an Optimist? Studying Cognitive Judgment Bias in Mice

Individuals differ in the way they perceive the world. From human psychological research, it is known that these differences become particularly evident in ambiguous situations: while some individuals interpret ambiguous information pessimistically, others bias their inter-pretations in a more optimistic way, referred to as cognitive judgement bias (CJB). CJBs have also been studied in non-human animals as tools for the assessment of affective states. However, the ecological and evolutionary relevance of CJB has so far been overlooked. We here aimed to transfer the concept of CJB to behavioural ecology. More specifically, we investigated the causes of differences in CJB in mice, focusing on both genetic and environmental factors. Furthermore, we assessed whether individual differences in CJB are repeatable over time, addressing the question whether “optimistic” and “pessimistic” decision styles, respectively, may represent stable traits. Thus, two strains of mice (C57BL/6J and B6D2F1N) were housed in two different environmental conditions: “scarce” or “complex”. While mice living in the “scarce environment” experienced standard housing conditions, those living in the “complex environment” had regular access to a super-enriched “playground”. To calculate the repeatability of “optimistic” and “pessimistic” decision styles, we assessed CJB four times across the course of seven weeks. Moreover, we assessed anxiety-like behaviour to detect potential differences in the effects of genetic or environmental factors on CJB and anxiety. While the selected genotypes and environments influenced some aspects of anxiety-like behaviour, no influence on CJB could be detected, indicating that CJB and anxiety might represent distinct systems. Remarkably, CJB was moderately repeatable, suggesting that decision-making under ambiguity constitutes a relatively stable trait and might even be considered an aspect of animal personality.