Specific AD impairment in concurrent performance of two memory tasks.

The current study examined the hypothesis that patients with Alzheimer's disease (AD) have a selective deficit in the coordination mechanism of the central executive, which is reflected in their inability to coordinate the performance of two tasks concurrently. One criticism of the previous studies in the literature is that they employ tasks that do not necessarily draw upon the separate peripheral mechanisms within working memory but combine a memory load with a perceptuomotor load. Therefore, the aim of the study was to examine the effects of AD and healthy adult ageing on a verbal memory plus visuospatial memory dual task paradigm. We investigated the performance of 15 AD patients and 20 healthy younger and 20 healthy older individuals on three different dual task combinations (i) digit recall and visual pattern recall; ii) digit recall and tracking; and iii) digit recall and articulatory suppression. The results demonstrate a significant dual task impairment in AD patients when two memory tasks are performed simultaneously compared to healthy younger and older adults. In contrast, there was not a significant age-related disruption in performance in healthy individuals compared to single task conditions. As the demands of each task were adjusted for individual ability levels, this provides further support for there being a specific AD dual task decrement in the mechanism responsible for coordinating dual task performance, which is separate from the resources needed to perform the tasks independently.