Once an optimist, always an optimist? Studying cognitive judgment bias in mice

Individuals differ in the way they judge ambiguous information: some individuals interpret ambiguous information in a more optimistic, and others in a more pessimistic way. Over the past two decades, such optimistic and pessimistic cognitive judgment biases (CJBs) have been utilized in animal welfare science as indicators of animals' emotional states. However, empirical studies on their ecological and evolutionary relevance are still lacking. We, therefore, aimed at transferring the concept of optimism and pessimism to behavioral ecology and investigated the role of genetic and environmental factors in modulating CJB in mice. In addition, we assessed the temporal stability of individual differences in CJB. We show that the chosen genotypes (C57BL/6J and B6D2F1N) and environments (scarce and complex) did not have a statistically significant influence on the responses in the CJB test. By contrast, they influenced anxiety-like behavior with C57BL/6J mice and mice from the complex environment displaying less anxiety-like behavior than B6D2F1N mice and mice from the scarce environment. As the selected genotypes and environments did not explain the existing differences in CJB, future studies might investigate the impact of other genotypes and environmental conditions on CJB, and additionally, elucidate the role of other potential causes like endocrine profiles and epigenetic modifications. Furthermore, we show that individual differences in CJB were repeatable over a period of seven weeks, suggesting that CJB represents a temporally stable trait in laboratory mice. Therefore, we encourage the further study of CJB within an animal personality framework.

Automated summary

Individuals differ in the way they judge ambiguous information, with some individuals being more optimistic and others more pessimistic. Optimistic and pessimistic judgment biases have been used as indicators of animals' emotional states in animal welfare science. This study explored the role of genetic and environmental factors in modulating judgment biases in mice and found that they did not have a significant influence on these biases. However, anxiety-like behavior was influenced by genotypes and environments. Additionally, the study showed that individual differences in judgment biases were stable over time. Further research is needed to investigate the impact of other factors on judgment biases and to understand their ecological and evolutionary relevance.