Electronic Thesis and Dissertation Repository


Master of Science




Dr. Martin Kavaliers

2nd Supervisor

Dr. Klaus-Peter Ossenkopp

Joint Supervisor


In humans, affective states can influence cognitive processes, resulting in a phenomenon referred to as “cognitive bias”. Rodents exhibit similar biases during the interpretation of ambiguous cues. It has been shown that cognitive bias shifts towards the negative valence (pessimism) when animals are under chronic stress manipulations. However, the effects of acute stress on cognitive bias have not been well established in an animal model. Here, a non-operant appetitive task using fluid rewards and distinct visual/tactile cues was developed to examine cognitive bias in male rats. Corticosterone was used to mimic stress levels similar to acute restraint stress. It was shown that under basal conditions, rats exhibited a positive cognitive bias (optimism), and that acute corticosterone administration resulted in a shift towards negative cognitive bias (pessimism). In all, this thesis provides a novel animal model to examine cognitive bias and the effects of acute stress manipulations.