(June 2007) Researchers are producing an increasingly complex and nuanced portrait of the aging brain, a topic of keen interest as the number and share of elderly people grows rapidly in the United States and around the world.
Recent research indicates that various mental skills decline at different rates as people age, and that trajectories of decline differ among people. Neuroimaging enables researchers to match changes in the brain's physical structure to changes in mental performance over time. Other recent work shows that people without dementia can improve their brain function or slow its decline somewhat.
The increased need to understand the effects of aging on mental abilities is driven by the potential consequences of demographic change. In most of the world, elderly people make up less than 15 percent of the population; by 2050, most nations will have at least that high a share of elderly people. In the United States and many other developed nations, older age groups will make up at least 30 percent of the population.
This worldwide aging is predicted to have an enormous impact on labor forces, health care systems, and family support networks. One goal of research is to reduce the strain on institutions and families by finding ways to prolong healthy years and minimize frail ones, both physical and mental.
Aging Minds Slow Down, at Different Rates for Different People
Memory and other cognitive skills decline from the 20s onward, according to a range of research, but the pace of decline varies. Some skills, such as vocabulary and general knowledge, often improve over time and do not decline until people are quite elderly. In general, people reach a cognitive peak in young adulthood, level off in their 50s and 60s, then decline slowly into the 80s, with a sharp drop in the years before they die.
People who have had less education or jobs that require little mental effort have lower cognitive skills at young ages and lose those skills at a sharper rate than people with more education or mentally demanding occupations. One theory is that the density of neural synapses grows with education level, protecting against cognitive impairment. Lack of physical activity and poor nutrition also appear to play a role in hastening cognitive decline.
"The aging mind is slower and more prone to error when processing information," according to Laura L. Carstensen, a psychology professor at Stanford University and director of its Center on Longevity. "It is less adept at considering old information in novel ways. Memory suffers. In particular, working memory—the ability to keep multiple pieces of information in mind while acting on them—declines with age. The ability to inhibit extraneous information when attempting to focus attention becomes impaired. Declines are especially evident on tasks that require effortful processing that relies on attention, inhibition, working memory, prospective memory, and episodic memory."
Brain Imaging Can Link Mental Slowing With Neural Decline
Some of the most innovative research on cognitive aging is being done with technology that shows an image of the brain at work. Functional magnetic resonance imaging (fMRI) or positron emission tomography (PET) scans of the brain can indicate which regions of the brain have deteriorated as well as which ones are active during specific tasks.
The scans confirm that brain volume shrinks with age, especially in areas toward the front of the brain that are believed to play a key role in cognitive decline. On the other hand, older brains show activity in several regions during some tasks, which researchers believe is a way of compensating for declines in any one section.
"On the one hand you really can see biological aging and its impact on the brain," said Denise Park, co-director of the Center for Healthy Minds at the University of Illinois-Urbana's Beckman Institute. "You also see how clever the brain is, and how new neural paths are developed and new neural tissue is brought to bear. The brain is working very hard to maintain equilibrium. The idea that the brain can change and adapt is exciting."
What Is the Real-Life Impact of Declining Cognitive Skills?
Although laboratory tests find that older people generally have slower brains and lower cognitive skills than younger ones, these declines do not always have an impact on day-to-day life. Older workers do as well in most jobs as younger ones, and most elderly people live independently, in part because many daily tasks are automatic or routine. In fact, research has found that old people are better at remembering to take prescription medications than the young or middle-aged, perhaps because the elderly have more fixed habits.
"It's not easy to find the impact of subtle declines in cognition in everyday life because most of the time your everyday life doesn't require all your cognition," Park said. "Where this comes to bear is in situations where you have to process a lot of information fast."
The ability to process information quickly is relevant for more than just playing video games or doing other tasks that demand a quick reaction time. A slower brain also is less able to process complicated information that requires the memory to record one piece of data before the next piece is absorbed. That could hinder an elderly person's ability to take in and respond to information from a physician presenting a complicated medical diagnosis, for example, or from someone conveying driving directions in a strange city.
Memory and other cognitive skills also can be affected by what researchers call the "social environment." In one experiment, lead author Tamara Rahhal, now of the University of Massachusetts, and other researchers compared performances on a memory test. Younger people scored higher than older ones when test takers were told to remember as many statements as possible from a list they were given. When they were told to "learn" as many as possible, age differences vanished. This suggests that older people's anxiety about their declining memories may worsen their ability to remember things.
When Baby Boomers Age
Some researchers believe that the baby-boom generation could be less at risk of cognitive decline than their parents because they have higher education levels, which may serve to increase the density of their neural synapses. People who engage in cognitive activities—reading a book, playing chess or crosswords, listening to a radio program—are less likely to lose their mental edge than those who do not. Older people can improve their memory capacity through training to the point that it equals that of untrained younger people, research shows.
"Now that we have these brain tools," Park said, "we are in the early stages of an era of [learning] what we can do to improve our cognitive function."
D'Vera Cohn is senior editor at the Population Reference Bureau.
Deborah E. Barnes et al., "The Relationship Between Literacy and Cognition in Well-Educated Elders," The Journals of Gerontology Series A: Biological Sciences and Medical Sciences 59, no. 4 (2004): 390-95.
Laura L. Carstensen, "Growing Old or Living Long: A New Perspective on the Aging Brain," Public Policy and Aging Report 17, No. 1, (2007): 13.
Dana A. Glei et al., "Participating in Social Activities Helps to Preserve Cognitive Function: An Analysis of a Longitudinal, Population-Based Study of the Elderly," International Journal of Epidemiology 34, no. 4 (2005): 864-71.
National Research Council, When I'm 64, ed. Laura L. Carstensen and Christine R. Hartel (Washington, DC: National Academies Press, 2002).
Denise Park and Norbert Schwartz, eds., Cognitive Aging: A Primer (Philadelphia: Psychology Press, 2000).
K. Warner Schaie and Laura L. Carstensen, eds., Social Structures, Aging, and Self-Regulation in the Elderly, (New York: Springer Publishing Co., 2006).
Sherry L. Willis et al., "Long-Term Effects of Cognitive Training on Everyday Functional Outcomes in Older Adults," Journal of the American Medical Association 296, no. 23 (2006): 2805-14.