Cognitive bias and emotion in neuropsychological models of depression

Neuropsychological models of depression were tested by examining encoding and recognition biases elicited by emotional stimuli manifested in regional brain wave activity. Participants were pre-exposed to emotional stimuli. These stimuli were presented again embedded in new stimuli, and event-related brain potentials (ERPs) were recorded while participants judged whether they had viewed each stimulus previously. Controls showed an enhanced P300 during encoding and reduced P300 during recognition of positive stimuli, indicating a response bias for positive information. In contrast, participants diagnosed with major depression showed no valence difference during encoding of new stimuli or recognition of old stimuli. These results suggest positive cognitive biases in controls and a lack of such a biases in depressed individuals. Additionally, regression analyses demonstrated that a substantial proportion of P300 variance was related to clinical scale scores. Especially at frontal sites, controls' P300 decreased with increasing scores while depressives' P300 increased with increasing scores. These findings will be discussed in the context of psychological and neuropsychological models of depression.