Heterogeneity of information-processing alterations according to dimensions of depression: an event-related...

To identify alterations in elementary cognitive operations according to dimensions of depression, two stages of information processing, namely the response choice and the motor preparation stages, were explored using an event-related potential paradigm in two subgroups of depressed patients (retarded and blunted affect versus anxious-agitated and impulsive) compared to controls. Two results are common to all depressed patients: a slow encoding of stimuli (P1 wave) and a prolonged processing of stimulus-response compatibility (after P3b). This is compensated by a global velocity increase in stimulus evaluation or decision making (P3b) in anxious-agitated patients or, on the contrary, cumulated with its velocity decrease in retarded-blunted-affect patients. Such results could provide an explanation for the massive retardation observed in blunted-affect patients, contrary to anxious-agitated patients, whose normal reaction times may come from a very high energetical involvement at the P3b level. Results as a whole suggest that impairments in blunted-affect patients concern effort mechanisms, whereas those in anxious-agitated patients concern perceptual processes.