Guarding against dementia and other cognitive aging disorders should start in midlife, suggests a growing body of cognitive aging research, giving further support to the ideas that learning throughout life and moderate exercise help protect the aging brain.
In midlife, most adults show stable cognitive function. But, according to a study by Pennsylvania State University researchers Sherry L. Willis, PhD, and K. Warner Schaie, PhD, 10 percent to 15 percent of people age 46 to 60 begin to show significant declines, while another 10 percent to 15 percent show significant gains.
One common denominator is that adults declining in cognitive functioning in midlife are more likely to have hypertension than adults who make cognitive gains, Schaie and Willis found. There also seems to be a physical difference in the brains of the two groups at old age: The size of the brain becomes smaller in those who showed the previous cognitive decline, Willis explains.
Their research also suggests that about 25 percent of middle-aged adults who show a decline in reasoning skills show further deterioration by age 75.
Meanwhile, research by Brandeis University's Margie E. Lachman, PhD, indicates that declines in memory and other cognitive abilities are not inevitable or irreversible and there is wide variation in the magnitude and patterns of change. Her research, based on findings from a large national study of people in midlife, suggests that those who believe that they have greater control over their lives and physical and mental functions are more likely to be happy and in good health. This sense of control is tied to better memory and intellectual functioning-especially in older adults, she says.
How can a sense of control affect cognitive decline? Older adults who experience memory lapses or physical decline may believe they can't control these processes. If this sense of lost control is accompanied by distress and anxiety, this may interfere with performance and prevent them from finding and using alternate strategies that can help compensate for mental and physical decline, says Lachman. In future research, she would like to identify factors that contribute to maintaining a personal sense of control.
"We are interested in modifiable identifying factors that can account for differences in the degree of cognitive decline in old age," says Lachman. "Who is able to maintain good memory in later life and why?"
So far, the evidence on protective factors shows a clear correlation between better cognitive function and advanced education and exercise, she explains. People with advanced education are more likely to use adaptive strategies to compensate for decline or changes in cognitive function. Previous research in animals has shown that exercise can create new neural connections. And a 2007 study in the Proceedings of the National Academy of Sciences (Vol. 104, No. 13) using MRI scans of humans found that exercise stimulates neural connections in a region of the brain within the hippocampus-known as the dentate gyrus-that is responsible for age-related memory decline. Preliminary findings suggest that people with lower levels of education may be able to improve cognitive function through exercise and through engaging in mentally stimulating activities. The cognitive stimulation may help them to develop and use the effective adaptive strategies that those with higher education more readily use, says Lachman.
More evidence on the ways education protects the brain comes from work by Columbia University's Yaakov Stern, PhD. His work suggests that people with higher IQs, more education, occupations that entail complex mental skills or those who participate in leisure activities have a reduced risk of developing Alzheimer's disease. In a 2006 review article in Alzheimer's Disease and Related Disorders (Vol. 20, No. 2), Sterns suggests that these factors may provide a kind of cognitive reserve: the ability to cope with brain damage by using mental coping mechanisms that work around the damage or even enlisting different areas of the brain to do what the damaged areas used to do.
Reserve may also come from a difference in brain size or number of neurons, adds Stern. This extra capacity would allow individuals to sustain a greater level of brain damage before showing signs of Alzheimer's or other forms of dementia.
Stimulating activities and exercise may also create new neurons, notes Stern. Some evidence suggests that engaging in these activities may prevent or slow Alzheimer's disease, he concludes.
To learn more about the progression of cognitive decline, Alzheimer's and other forms of dementia, researchers must conduct more studies that include healthy older adults, says Martha Storandt, PhD, the recipient of APA's 2007 Committee on Aging Award for the Advancement of Psychology and Aging.
"We need more longitudinal studies involving people who are not in the initial stages of dementia," says Storandt. "We need to use what we know to improve our measurement of various aspects of cognition in addition to memory in order to determine what is and is not affected in the earliest stages of the disease."