Individual differences in affective processing in laboratory rats and implications for animal welfare

This study will investigate how the way in which an animal processes affective information influences its welfare in the face of changing opportunities and challenges. Recent research using the translational judgement bias task developed in our lab and designed to assess animal affective (emotional) state (JBT; >200 published studies), indicates that individuals vary consistently in whether they anticipate positive or negative outcomes when making decisions under uncertainty. In humans, such individual differences in affective processing (‘optimism’ / ‘pessimism’) are known to predict emotional state, wellbeing and vulnerability to affective disorders such as depression, and in non-human animals there is early evidence that ‘pessimistic’ phenotypes may indeed be more vulnerable to stress. In this study, we will test the hypothesis that personality differences in affective processing have an impact on an animal’s affective state and welfare. We will use a reaction norm approach that allows us to quantify not just individual differences in mean responses (personality), but also individual differences in how responses change across context / time (plasticity) and in the variability of responding within a given context (predictability). We will apply this approach to parameters extracted from JBT data using computational modelling which characterises aspects of affective processing such as optimism-bias and reward/punishment sensitivity. These parameters are known to play a role in how individuals respond to challenge. We will work with laboratory rats, the species we used to develop the original JBT, and we will study both sexes. Sex bias in favour of males remains pervasive in many studies partly because it is assumed that females, due to the oestrous cycle, produce more variable data. Our predictability readouts will address this issue directly. Once individuals have been characterised, we will monitor their welfare in contexts that vary in opportunity and threat, generating a set of reaction norms that summarise how their welfare changes with changing availability of opportunity (enrichment provision) and changing presence of threat (unpredictable events). We will investigate links between individual affective processing characteristics and welfare reaction norms to test hypotheses including whether more ‘optimistic’ animals, especially those showing predictable rather than variable levels of ‘optimism’, cope better with challenge (e.g. show flattening of reaction norms across contexts varying in threat). Objectives: • Objective i: to use repeated JBT tests to quantify individual differences in personality, plasticity, and predictability of extracted affective processing parameters such as optimism-bias and reward/punishment sensitivity in male and female rats • Objective ii: to use welfare indicators to measure individual welfare reaction norms across environments varying in opportunity and threat • Objective iii: to evaluate whether and how individual affective processing characteristics measured in Obj. i predict welfare reaction norms measured in Obj. ii.