Alzheimer's disease, but not ageing or depression, affects dual-tasking.

Two experiments are reported that assess dual task performance in Alzheimer's disease (AD), in chronic depression and in healthy old age. Results suggest that dual task impairments are present in AD but are not shown in depression. This is true even when episodic memory performance is equated between the groups. These results, together with those of previous studies, point to dual task performance as an aid to diagnosis of AD relative to depression. This is of particular relevance when episodic memory tests cannot distinguish between the two conditions. The dual task paradigm appears to have considerable promise in assisting the early detection of the specific cognitive deficits associated with AD, and in monitoring their progression, both in the laboratory setting and in everyday tasks. Results also are of theoretical interest in pointing to a specific dual task coordination function in the healthy human cognitive system that allows for the coordination of two tasks performed simultaneously and which is damaged in AD but not in depression.