A spatial judgement task to determine background emotional state in laboratory rats, Rattus norvegicus

Humans experiencing different background emotional states display contrasting cognitive (e.g. judgement) biases when responding to ambiguous stimuli. We have proposed that such biases may be used as indicators of animal emotional state. Here, we used a spatial judgement task, in which animals were trained to expect food in one location and not another, to determine whether rats in relatively positive or negative emotional states respond differently to ambiguous stimuli of intermediate spatial location. We housed 24 rats with environmental enrichment for 7 weeks. We removed the enrichment from half the animals prior to the start of training to induce a relatively negative emotional state, whereas we left it in place for the remaining rats. After 6 training days, the rats successfully discriminated between the rewarded and the unrewarded locations in terms of an increased latency to arrive at the unrewarded location, with no housing treatment difference. The subjects then underwent 3 days of testing in which three ambiguous ‘probe’ locations, intermediate between the rewarded and the unrewarded locations, were introduced. There was no difference between the treatments in the rats' judgement of two of the three probe locations, the exception being when the ambiguous probe was positioned closest to the unrewarded location. This result suggests that rats housed without enrichment, and in an assumed relatively negative emotional state, respond differently to an ambiguous stimulus compared to rats housed with enrichment, providing evidence that cognitive biases may be used to assess animal emotional state in a spatial judgement task.