Loss of competency, or decision-making capacity, ^[1] is an inevitable consequence of Alzheimer's disease (AD). ^[2] As capacities for memory, judgment, reasoning, and planning erode, AD patients lose decision-making capacity in every sphere of life. Specific competencies that are lost include the capacity to drive, to manage finances, to make medical treatment decisions, to live independently, and, ultimately, to manage all personal affairs. ^[2] Loss of competency in dementia has crucially important consequences for patients and their families, health care and legal professionals, and for society as a whole. ^[2]

Although competency is ultimately a legal status, the realities of clinical practice compel physicians and other health care professionals to make competency judgments on a daily basis. ^[1] Of particular importance to physicians is the question of whether an AD patient is competent to consent to treatment. ^[3] This competency is an essential element of the doctrine of informed consent, ^[4-6] which requires that consent to treatment be voluntary, informed, and also competent. ^[7] Issues concerning this competency are also unique to the medical setting because they arise in the hospital or clinic, involve a health care professional as a decision maker, and are rarely subject to judicial review. ^[4] Henceforth, in this article we use the general term competency to refer to the capacity to consent to medical treatment.

Given the importance of competency loss in dementia, there is surprising little empiric research. ^[8] Little is known about the natural history of competency loss in dementia or about the cognitive and behavioral changes associated with competency loss. Neuropsychological studies of competency loss have potentially significant theoretical and clinical value; they can illuminate the relationship of specific cognitive changes to functional decline in dementia, serve as an important bridge between developments in neuroscience and law, alert clinicians to specific cognitive …