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  • The Structure and Function of the Brain Change with Age

  • Cognitive Decline Is Dramatic in a Small Percentage of the Elderly

  • Alzheimer Disease Is the Most Common Senile Dementia

  • The Brain in Alzheimer Disease Is Altered by Atrophy, Amyloid Plaques, and Neurofibrillary Tangles

    • Amyloid Plaques Contain Toxic Peptides That Contribute to Alzheimer Pathology

    • Neurofibrillary Tangles Contain Microtubule-Associated Proteins

    • Risk Factors for Alzheimer Disease Have Been Identified

  • Alzheimer Disease Can Be Diagnosed Well but Available Treatments Are Poor

  • Overall View

The average life span in the United States in 1900 was about 50 years. Today it is approximately 76 years for men and 81 for women (Figure 59–1), and is higher still in 30 other countries. These increases result largely from a reduction in infant mortality, the development of vaccines and antibiotics, better nutrition, improved public health measures, and advances in the treatment and prevention of heart disease and stroke. Because of increased life expectancy, along with the large cohort of "baby boomers" born after World War II, the elderly are the most rapidly growing segment of the U.S. population.

Figure 59–1
Human life span is increasing.

Changes in human longevity illustrate the rapid extension in life span that has occurred in the United States over the past 100 years. (Modified, with permission, from Strehler 1975; Arias 2004.)

Increased longevity is a double-edged sword: Age-related cognitive alterations are increasingly prevalent. Their extent varies widely among individuals. For many, the alterations are mild and have relatively little impact on the quality of life—the momentary lapses we jokingly call "senior moments." Other cognitive impairments, although not debilitating, are troubling enough to hinder the ability of the elderly to manage their lives independently. At the far extreme are the severe dementias, which rob the elderly of memory and reasoning. Of these, Alzheimer disease is the most prevalent.

As the population ages, research on age-related changes in the brain has become a more prominent area of focus for neuroscientists, neurologists, and psychologists. The main aim of research on aging has been to find treatments for Alzheimer disease and other dementias, but it is also important to understand the normal process of cognitive decline with age. After all, age is the greatest susceptibility factor for a wide variety of neurodegenerative disorders. Understanding what happens to our brains as we age may not only improve the quality of life for the general population but may also provide clues that will eventually help us vanquish seemingly unrelated pathological changes.

With this in mind, we begin this chapter with a consideration of how the normal brain ages. We then proceed to consider the broad range of pathological changes in cognition, and finally focus on Alzheimer disease, the most common cause of severe memory loss and intellectual deterioration in the elderly.

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