Abstract
Cognitive processes are often biased by emotions. In humans, affective disorders are accompanied by pessimistic judgement, while optimistic judgement is linked to emotional stability. Similar to humans, animals tend to interpret ambiguous stimuli negatively after experiencing stressful events, although the long-lasting impact on judgement bias has rarely been investigated. We measure judgement bias in female chicks (Gallus gallus domesticus) after exposure to cold stress, and before and after exposure to additional unpredictable stressors. Additionally, we explore if brain monoamines can explain differences in judgement bias. Chicks exposed to cold stress did not differ in judgement bias compared to controls, but showed sensitivity to additional stressors by having higher motivation for social reinstatement. Environmental complexity reduced stress-induced negative judgement bias, by maintaining an optimistic bias in individuals housed in complex conditions even after stress exposure. Moreover, judgement bias was related to dopamine turnover rate in mesencephalon, with higher activity in individuals that had a more optimistic response. These results demonstrate that environmental complexity can buffer against negative effects of additive stress and that dopamine relates to judgement bias in chicks. These results reveal that both internal and external factors can mediate emotionally biased judgement in animals, thus showing similarities to findings in humans.
Highlights
It is well known from human psychology that emotions can affect several aspects of cognition
A dopamine antagonist abolished optimistic judgement observed in bumblebees (Bombus terrestris audax) after sucrose consumption[42], suggesting that at least dopamine is involved in regulating judgement biases in these species
The probabilities of approaching ambiguous cues were over chance level, guiding our interpretation of responses measured in the judgement bias task as measuring variation in optimistic bias[9,27]
Summary
It is well known from human psychology that emotions can affect several aspects of cognition (for review, see refs[1,2]). Anxiety and depression associate with negative biases (e.g refs[1,2]) Such emotionally biased information processing is termed cognitive judgement bias (e.g. refs2,3), judgement bias, or interpretation bias[6]. Juvenile stress and chronic unpredictable stress during adolescence had a long-term effect on judgement bias[23,33], suggesting that stress early in life can have lasting effects on judgement biases, in non-human animals. There is still limited knowledge about the impact of brain monoamines on judgement biases in other species, and few studies have looked at un-manipulated levels of these brain monoamines in animals with varying affective state (but see ref.[16])
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