Positive and negative cognitive biases in a cockroach

Understanding the mental experiences of animals is key for managing them and mapping the evolution of cognitive complexity. Emotional and affective states are fundamental to these goals as their presence indicates the potential for negative welfare states and so suffering. However, until recently the potential for affective states in invertebrates has been underappreciated, especially for positive affective states where research is limited to a single order. Here, we adapt cognitive bias tests to examine both negative (pessimistic) and positive (optimistic) bias in cockroaches (Blaptica dubia) in order to expand the taxonomic reach of affective state research and to provide a rare test for positive affective states in an invertebrate. We trained cockroaches to associate two different odours with either positive reinforcement or positive punishment and then assessed their reactions to ambiguous stimuli (a range of mixtures of the trained odours). We found that cockroaches exposed to light were more pessimistic (negative affective state) than controls, while those exposed to the scent of opposite sex conspecifics were marginally more optimistic (positive affective state) than controls. Our results are therefore consistent with the potential for affective states in cockroaches and for positive affective states in invertebrates more widely, indicating a previously unexpected level of motivational complexity.