Dissociation of vascular dementia and Alzheimer's disease using a sequential working memory and recognition task

Previous research suggests that it is possible to differentiate between patients with dementia due to subcortical ischemic white matter disease (i.e. vascular dementia---VaD) from those with Alzheimer's disease (AD), as the former generally demonstrate executive dysfunction within the context of preserved recognition memory (i.e. encoding ability) whereas the opposite pattern is present in patients with AD. Executive abilities, specifically working memory, are important in utilizing the temporal aspects of memory (e.g. the sequence in which events occurred). Thus, a novel test was developed wherein participants were asked to sequence and then recognize a series of letters from among distracters with the expectation that the VaD patients would perform more poorly on the sequencing task whereas those with AD would do worse on the recognition component. Participants with mild AD (n=14), mild VaD (n=13), and healthy controls (n=10) were administered the experimental task and traditional neuropsychological tests of working memory and recognition memory. The patients were diagnosed with either AD or VaD and were required to have either low or high white matter damage, respectively, as evidenced by MRI scans. The VaD group performed worse during the sequencing task and also demonstrated difficulty utilizing the temporal aspects of memory. There was some evidence that encoding was relatively preserved in the VaD group compared to the AD patients following even the short delays used in this study (i.e. 15 seconds). Thus, the results support the relationship between executive abilities and the temporal aspects of memory and suggest that white matter damage can result in deficits analogous to those observed with cortical lesions. Additionally, the methods used in the experimental task may hold promise for examining such abilities within these and other populations.