Alzheimer's disease (otherwise known as AD) was first diagnosed in 1906 by the German doctor Alois Alzheimer. Serious research on the disease did not begin, however, until the 1950's when Alzheimer's became more clearly distinguished from other types of dementia. AD is now, by far, the most common and possibly the most serious type of dementia. Approximately 2.5 million people over the age of 65 in the United States have this disease. It has been predicted that AD could triple over the next 50 years as increasing numbers of people live to older ages (Santrock, 1999.) Dementia (defined as memory impairment accompanied by aphasia, apraxia, or agnosia) is the critical feature of Alzheimer's disease. Associated symptoms include depression, irritability, mood liability, anxiety, and sleep disturbance (Grossberg, 2003). .
Dementias are among the most complex and debilitating of mental disorders among the elderly. Alzheimer's disease is a progressive, irreversible brain disorder that is characterized by gradual deterioration of memory reasoning, language, and eventually physical functioning. Early in the course of AD, damage occurs to the medical temporal lobe (MTL), leading to impairment in declarative memory, as well as the ability to learn new fact and events. The neuropathology becomes progressively widespread, involving particularly the association areas of the temporal, parietal, and frontal lobes (Reber, Martinez, & Weintraub, 2003). Sommers (1998) notes that: "AD also affects two major abilities: perceptual normalization and lexical discrimination. They are essential for recognition of spoken words. Both of these capacities are independent of deficits in other cognitive abilities such as memory and processing speed." .
Autopsies of patients with Alzheimer's disease reveal both neurofibrillary tangles, which are twisted and distorted nerve fibers, and senile plaques or microscopic lesions in the neurons (Alloy, Jacobson, & Acocella, 1999.
