Trait "pessimism" is associated with increased sensitivity to negative feedback in rats.

Several cognitive theories of depression have proposed that cognitive judgment bias determines individual vulnerability to this disorder. Indeed, we have recently demonstrated a relationship between pessimistic judgment bias and vulnerability of rats to the stress-induced anhedonia, and a negative correlation between the level of pessimism and motivation. To further characterize the effects of trait pessimism on cognitive processes associated with depression, in the present study we compared the sensitivity of rats displaying optimistic and pessimistic traits to positive and negative feedback. The animals were initially trained and tested in the rat version of the probabilistic reversal-learning (PRL) task, which allowed for the assessment of feedback sensitivity in individual animals. Subsequently, the rats were re-trained and tested in a series of ambiguous-cue interpretation (ACI) tests, which allowed for the classification of animals displaying "optimistic" and "pessimistic" traits. The "pessimistic" rats were significantly more sensitive to negative feedback than their "optimistic" conspecifics, as indicated by an increased proportion of lose-shift behaviors. The results of our study demonstrate the interrelation and co-existence of two cognitive biases that may predict vulnerability to depressive disorder.