supply to the brain, typically involving a series of mini-strokes. The symptoms of this dementia depend on where in the brain the strokes occurred and whether the blood vessels affected were large or small. Repeated injury can cause progressive dementia over time, while a single injury located in an area critical for cognition such as the hippocampus, or thalamus, can lead to sudden cognitive decline. Elements of vascular dementia may be present in all other forms of dementia. Brain scans may show evidence of multiple strokes of different sizes in various locations. People with vascular dementia tend to have risk factors for disease of the blood vessels, such as tobacco use, high blood pressure, atrial fibrillation, high cholesterol, diabetes, or other signs of vascular disease such as a previous heart attack or angina. Lewy bodies The prodromal symptoms of dementia with Lewy bodies (DLB) include mild cognitive impairment, and delirium onset. The symptoms of DLB are more frequent, more severe, and earlier presenting than in the other dementia subtypes. Dementia with Lewy bodies has the primary symptoms of fluctuating cognition, alertness or attention; REM sleep behavior disorder (RBD); one or more of the main features of parkinsonism, not due to medication or stroke; and repeated visual hallucinations. The visual hallucinations in DLB are generally vivid hallucinations of people or animals and they often occur when someone is about to fall asleep or wake up. Other prominent symptoms include problems with planning (executive function) and difficulty with visual-spatial function, and disruption in autonomic bodily functions. Abnormal sleep behaviors may begin before cognitive decline is observed and are a core feature of DLB. RBD is diagnosed either by sleep study recording or, when sleep studies cannot be performed, by medical history and validated questionnaires. Parkinson's disease Parkinson's disease is a Lewy body disease that often progresses to Parkinson's disease dementia following a period of dementia-free Parkinson's disease. Frontotemporal Frontotemporal dementias (FTDs) are characterized by drastic personality changes and language difficulties. In all FTDs, the person has a relatively early social withdrawal and early lack of insight. Memory problems are not a main feature. There are six main types of FTD. The first has major symptoms in personality and behavior. This is called behavioral variant FTD (bv-FTD) and is the most common. The hallmark feature of bv-FTD is impulsive behavior, and this can be detected in pre-dementia states. In bv-FTD, the person shows