Neuropsychological concomitants of major depression

by Hillis, Sarah

The limits of the cognitive deficits associated with depression were investigated with a battery of standardized neuropsychological tests- In addition, the various perspectives regarding the mechanism responsible for the cognitive changes were investigated using a dual-task paradigm. By comparing a clinically depressed group and a non-depressed control group as they perfomed a finger tapping task and either a simultaneous automatic or a relatively attention-demanding cognitive task, it was possible to address the issue of depression-related decreases in processing capacity. The proportional change in tapping rate, in the dual-task condition, relative to the single-task condition, served as an indicator of the resources necessary to perfonn the cognitive task. By comparing responsiveness to a task emphasis manipulation, designed to shift priority from a manual to a cognitive task, it was possible to address the issue of resource allocation. Finally, by comparing left- and right-hand decrement scores during simultaneous performance of either a verbal or a spatial task, it was possible to address the issue of hemispheric specialization. The results do not provide strong support for the theory of a decrease in central capacity in major depression. Instead, the findings are suggestive of a capacity limitation specific to processing spatial information. As such, the findings are more consistent with a multiple resource model of attention. In addition, the results offer some support for the model of impaired allocation of attentional resources in response to task demands- Finally, the results are suggestive of atypical hemispheric involvement when processing information in the depressed state. iii