Alzheimer's disease (AD) is the most common cause of dementia in older adults. The cause of the disease still is unknown and there is no cure. In 1999, an estimated 4 million people in the United States suffered from AD. While the disease usually begins after age 65, and risk of AD goes up with age, it is important to note that AD is not a normal part of aging. The aging of the baby boom population has made AD one of the fastest growing diseases; estimates indicate that by the year 2040, some 14 million people in the United States will suffer from AD.
Cognitive deficits are the primary symptoms of AD. Early on, there is mild memory impairment; as the disease progresses, memory problems increase and difficulties with language are generally observed, including word-finding problems and decreased verbal fluency. Many patients also exhibit difficulty with visuospatial tasks. Personality changes are common, and patients become disoriented as the memory problems worsen. A progres sive deterioration of function follows and, at late stages, the patient is bedridden, nearly mute, unresponsive, and incontinent. A definitive diagnosis of AD is not possible until autopsy, but the constellation of symptoms and disease progression allows a reasonably certain diagnosis.
Gross pathology consistent with AD is mild to severe cortical atrophy (depending on age of onset and death). Microscopic pathology indicates two classic signs of the disease even at the earliest stages: the presence of senile plaques (SPs) and neurofibrillary tangles (NFTs). As the disease progresses, synaptic and neuronal loss or atrophy and an increase in SPs and NFTs occur.
While many neurotransmitter systems are implicated in AD, the most consistent pathology is the loss or atrophy of cholinergic neurons in the basal forebrain. Medications that ameliorate the cognitive symptoms of AD are cholinergic function enhancers. These observations emphasize the importance of cholinergic systems in cognitive function.
coordinate aspects of understanding and executing speech and language skills.
Clinical evidence indicates that Wernicke's area is essential for the comprehension, recognition, and construction of words and language, whereas Broca's area is essential for the mechanical production of speech. Patients with a defect in Broca's area show evidence of comprehending a spoken or written word but they are not able to say the word. In contrast, patients with damage in Wernicke's area can produce speech, but the words they put together have little meaning.
Language is a highly lateralized function of the brain residing in the left hemisphere (see Clinical Focus Box 7.1). This dominance is observed in left-handed as well as right-handed individuals. Moreover, it is language that is lateralized, not the reception or production of speech. Thus native signers (individuals who use sign language) that have been deaf since birth still show left-hemisphere language function.
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