Alzheimer's disease is the most common form of dementia. However, there is increasing evidence of a relationship between vascular dementia, which is characterized by the presence of cognitive deficits due to cerebrovascular lesions, and Alzheimer's disease. This raises questions regarding the distinction between Alzheimer's disease and vascular dementia, and the need for a better understanding of their similarities and differences. Importantly, a large proportion of persons diagnosed with Alzheimer's disease actually have mixed dementia; that is, they have vascular abnormalities in addition to Alzheimer's disease. It is important to identify these individuals, because clinicians don't use the same management approach for patients with only vascular dementia, patients with only Alzheimer's disease or those with mixed dementia. Unfortunately, it is difficult to diagnose these individuals with current clinical tools.

The goal of this study is to assess whether magnetic resonance imaging, a brain imaging technique, can help identify individuals with Alzheimer's disease, vascular dementia or mixed dementia. We will also focus on a group of patients with very mild cognitive deficits. The brain of these participants will first be analyzed to identify brain anomalies. Patients will then be evaluated using neuropsychological tasks (of episodic memory, executive functions, psychomotor speed), and through neuropsychiatric examination. Participants will be followed repeatedly over a long period of time to assess the nature and progression of their deficits. This will allow a clearer understanding of whether the clinical outcome of those patients was primarily determined by brain abnormalities.