Cognitive bias and emotion in neuropsychological models of depression

Neuropsychological models of depression were tested by examining encoding a nd recognition biases elicited by emotional stimuli manifested in regional brain wave activity. Participants were pre-exposed to emotional stimuli. Th ese stimuli were presented again embedded in new stimuli, and event-related brain potentials (ERPs) were recorded while participants judged whether th ey had viewed each stimulus previously. Controls showed an enhanced P300 du ring encoding and reduced P300 during recognition of positive stimuli, indi cating a response bias for positive information. In contrast, participants diagnosed with major depression showed no valence difference during encodin g of new stimuli or recognition of old stimuli. These results suggest posit ive cognitive biases in controls and a lack of such a biases in depressed i ndividuals. Additionally, regression analyses demonstrated that a substanti al proportion of P300 variance was related to clinical scale scores. Especi ally at frontal sites, controls' P300 decreased with increasing scores whil e depressives' P300 increased with increasing scores. These findings will b e discussed in the context of psychological and neuropsychological models o f depression.