Motivational effects on neuropsychological functioning: comparison of depressed versus nondepressed individuals

The neuropsychology of depression was examined in terms of organic and motivational hypotheses. Thirty medication-free depressed outpatients (selected according to Diagnostic and Statistical Manual of Mental Disorders [American Psychiatric Association, 1980] criteria for major depression) and 30 nondepressed normal controls were evaluated with a variety of neuropsychology measures. Prior to testing, subjects were assigned randomly to either a motivated or nonmotivated condition. A task measuring level of motivation demonstrated efficacy of the two motivation conditions. A 2 x 2 (Diagnosis x Motivational Level) multivariate analysis of variance of all the dependent measures revealed a significant main effect for depression, but no effect for motivation and no interaction. Univariate analyses demonstrated that the depressed group was impaired on visuospatial short-term memory and learning and on verbal learning. The finding of neuropsychological deficit in depressed subjects was not attributable to motivational factors. The problems with conceptualizing depression as a right-hemisphere dysfunction are discussed.