Elevated levels of the stress hormone, corticosterone, cause \u2018pessimistic\u2019 judgment bias in broiler chickens

Oluwaseun S. Iyasere,Andrew P. Beard,Melissa Bateson,Jonathan H. Guy

doi:10.1038/s41598-017-07040-y

Oluwaseun S. Iyasere, Andrew P. Beard + Show 2 more

Open Access

https://doi.org/10.1038/s41598-017-07040-y

Copy DOI

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.

Highlights

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
Since stress has a role in the development, maintenance and re-emergence of affective disorders[7], it is a plausible hypothesis that the physiological stress response is involved in the mechanism underlying the induction of pessimistic judgment biases
Our aims were to develop a judgment bias task for chickens involving punishment that did not in itself impose chronic stress on the birds, and to use this task to test the effects of non-invasively-ingested corticosterone (CORT) on decision making

Summary

Introduction

Pessimistic judgment biases occur when subjects interpret neutral or ambiguous information negatively, displaying either an increased expectation of punishment and/or a decreased expectation of reward in response to ambiguous cues[1] Pessimism of these types is a common symptom of human affective disorders such as anxiety and depression[2, 3]. Exposure to stressors triggers a highly conserved series of neuroendocrine responses throughout the body This involves an immediate (0–20 minutes) response orchestrated by catecholamine neurotransmitters (e.g. noradrenaline and dopamine) and a medium-term (3–120+ minutes) response orchestrated by non-genomic and subsequently genomic effects of corticosteroid hormones (predominantly cortisol in humans but corticosterone in rodents and birds; both referred to as CORT)[8, 9]. The early phase of the stress response produces an immediate, hyper-vigilant state accompanied by an increased emphasis on rapid, automatic, stimulus www.nature.com/scientificreports/

Objectives

Methods

Results

Conclusion