Working Memory Functioning in Alzheimer's Disease and Vascular Dementia

Overview

The aim of the present study is to investigate potential cognitive mechanisms contributing to working memory impairment in Alzheimer's disease and vascular dementia. The investigators consider a new hypothesis suggesting that difficulties in mobilizing maintenance strategies of information could explain this working memory deficit. More specifically, the investigators assume that patient groups will have difficulties in employing both refreshing and elaborative strategies during a working memory task (i.e., complex span task), as compared to a control group.

Working memory is considered as a central hub in human cognition. Good working memory capacities are fundamental for daily life. However, previous research has indicated that patients with Alzheimer's disease or vascular dementia have significant working memory impairment. Currently, there is no consensus on the cognitive mechanisms responsible for this deficit. Prior findings have highlighted that patients with Alzheimer's disease and/or vascular dementia demonstrate specific difficulties in dual-task situations. In this context, the investigators hypothesize that the continuous alternation between maintenance and processing phases involved in working memory could be impaired for these patients. Thus, the aim of the present study is to investigate if patients with Alzheimer's disease and/or vascular dementia can use maintenance strategies of information in working memory, as typically observed in individuals without cognitive impairments. To this end, the investigators propose a short working memory task in which they manipulate the opportunities to use refreshing strategies and elaborative strategies. The investigators expect that patients with Alzheimer's disease, vascular dementia, or mixed dementia will benefit less than healthy older adults from the increased opportunities to employ refreshing and elaboration. These difficulties could account for the impaired working memory performance associated with these diseases. In a second step, the investigators formulate distinctive hypotheses between patient sub-groups: * On the one hand, Alzheimer's disease is characterized by salient impairment of episodic long-term memory. Consequently, the investigators hypothesize that the working memory decline could be related to this deficit in long-term memory. Specifically, patients with Alzheimer's disease would have greater difficulty in implementing elaboration strategies. Thus, these patients' recall performance should benefit less from semantic links between the to-be-remembered items compared to patients with vascular dementia. * On the other hand, vascular dementia is characterized by a significant impairment of executive functioning. Thus, the investigators hypothesize that the working memory decline could be related to difficulties in implementing refreshing strategies (i.e., voluntary control of attention). Thus, the recall performance of these patients should benefit less from increased free time during the task, compared to patients with Alzheimer's disease. * Finally, very few studies have been carried out on patients with mixed dementia (from both Alzheimer's disease and vascular dementia). The investigators assume that the recall performance of these patients will benefit less from elaborative opportunities compared to patients with dementia vascular, and less from refreshing opportunities compared to patients with Alzheimer's disease.