Elevated levels of the stress hormone, corticosterone, cause ‘pessimistic’ judgment bias in broiler chickens

Abstract

Pessimistic judgment biases, whereby humans or non-human animals interpret ambiguous information negatively, are hypothesised to be one of the suite of adaptive changes that comprise the vertebrate stress response. To test this hypothesis, we asked whether experimentally elevating levels of the glucocorticoid stress hormone, corticosterone, in broiler chickens produced a pessimistic judgment bias. We trained young chickens to discriminate a stimulus (paper cone) placed at two locations in an arena, one associated with reward (mealworms) and one with punishment (air puff). During seven days of non-invasive administration of either corticosterone or vehicle control, we tested the birds’ responses to the cone placed at ambiguous locations between the trained locations. Corticosterone-treated birds were more likely than controls to respond as if punishment was likely when the cone was placed near to the punished location. The degree of this ‘pessimism’ was associated with smaller relative spleen weight, which is a documented consequence of chronic stress in chickens. We conclude that changes in corticosterone levels in chickens are sufficient to cause a specific change in decision making, dubbed ‘pessimism’, whereby corticosterone-treated birds showed an increased expectation of punishment in the face of ambiguous information. Pessimism could be a useful welfare indicator in chickens.

Aggressive encounters lead to negative affective state in fish

“…The findings presented here suggest that these responses may be controlled by changes in affective state, and future work could examine exactly how affect is linked to proactive and reactive responses. Additionally, losing aggressive encounters leads to a rise in corticosteroids in fish [24][25][26] which has been shown to be related to pessimistic judgement biases in rats [27,28] and chickens [29]. Whether corticosteroids mediate the observed pessimistic judgement bias in Murray cod remains to be confirmed, but the present results are in agreement with the involvement of corticosteroids in pessimistic judgement biases.…”

Developmental history and stress responsiveness are related to response inhibition, but not judgement bias, in a cohort of European starlings (Sturnus vulgaris)

“…The direction of this association is not intuitive. Moreover, it is not the association we predicted on the basis of previous experimental work (Enkel et al 2010; Iyasere et al 2017). Those experiments suggest that higher circulating CORT induces greater pessimism.…”

“…The association between mood disorders and early-life adversity in humans is thought to be mediated by persistent changes in the HPA axis and circulating glucocorticoid hormone concentrations (Holsboer 2000; Heim et al 2008). Two recent experimental studies, one in rats and one in chickens, have suggested that increasing levels of the glucocorticoid hormone corticosterone (CORT) may cause a switch to more ‘pessimistic’ performance on judgement bias tasks (Enkel et al 2010; Iyasere et al 2017). In the current cohort of birds, we did not manipulate CORT levels experimentally.…”

Heritabilities and co-variation among cognitive traits in red junglefowl

“…This is because reactive/slow types are considered to be both more competent in reversal learning and more susceptible to stress [26,85]. In turn, both acute and chronic stress have been linked to negative affective states, and, thereby, pessimistic-like behaviour [56,[86][87][88]. Another possible explanation for our findings may entail between-individual differences in persistence underlying both reversal learning [89] and optimistic response to ambiguous cues [90].…”