The Science of Aging Brains
Science is reshaping what we know about getting older. (The news is better than you think.)
Over the years, Timothy Salthouse has tested more than 8,000 people in his lab at the University of Virginia, assessing their memories, problem-solving skills, and other mental functions to see how the brain fares with age. The results have been predictably dismal: after age 25 or so, it’s pretty much all downhill. (No news there: Plato wrote that when a man grows old, he "can no more learn much than he can run much.") But something bothered Salthouse about the results, and on a late spring day in his office at the Russell Sage Foundation on New York’s Upper East Side, where he has been a visiting scholar this year, he whips out a graph that captures the paradox.
The graph shows two roller-coastering lines. One represents the proportion of people of each age who are in the top 25 percent on a standard lab test of reasoning ability—thinking. The other shows the proportion of CEOs of Fortune 500 companies of each age. Reasoning ability peaks at about age 28 and then plummets, tracing that well-known plunge that makes those older than 30 (OK, fine, 40) cringe: only 6 percent of top scorers are in their 50s, and only 4 percent are in their 60s. But the age distribution of CEOs is an almost perfect mirror image: it peaks just before age 60. About half are older than 55. And the number under 40 is about zero.
One can make a cheap joke out of this (so that’s why AIG, GM, Lehman, et al. tanked: the smartest people weren’t running them), but Salt-house deduces more counterintuitive, and hopeful, lessons. The first is that in real life, rather than in psych labs, people rely on mental abilities that stand up very well to age and discover work-arounds for the mental skills that do fade. The second is that some mental abilities actually improve with age, and one of them may be the inchoate thing called wisdom, which is not a bad thing to have when running a company. Little of the gloom-and-doom conventional wisdom about what happens to the brain as we age, says Salt-house, "is based on well-established empirical evidence." Instead, he says, much of it seems to be "influenced as much by the authors' preconceptions and attitudes as by systematic evaluation" of solid data.
Insights like that are producing a dramatic, and hopeful, rethinking of what happens to the mind and brain as we age. Some of the earlier bad-news findings are being questioned as scientists discover that the differences between today’s 20-year-old brains and 80-year-old brains reflect something other than simple age, and instead have to do with how people live their lives. And a deeper understanding of normal cognitive aging is producing interventions that, because they target the cell-level brain changes that accompany aging, promise to be more effective than memory exercises and crossword puzzles.
Take the claim that brain volume shrinks beginning in our 30s. Earlier studies suggested that the prefrontal cortex (just behind the forehead) takes the greatest hit; this is the region responsible for executive function such as forethought, reasoning, and "fluid" intelligence—the ability to figure out, for instance, which letter best continues the sequence G-B-F-C-E. But those data, it turns out, may be skewed by the inclusion of people who have very early dementia—so early that they have no symptoms, explains neuroscientist John Morrison of Mount Sinai School of Medicine in New York, but still have neuronal loss and thus volume loss in their prefrontal cortex. If only truly healthy people were studied, there might be no such volume loss, he says.
Earlier studies also found that myelination, the fatty insulation around neurons, peaks in our late 20s and then declines. Because myelin allows electrical signals to travel through the brain more quickly and efficiently, its loss means it takes longer to connect a face with a name, a book with an author, or any other facts. Its loss also makes the brain "noisier," explains neuroscientist Henry Mahncke of Posit Science: "It’s like a radio that is no longer precisely tuned to a station. It takes the brain more effort to find that signal, and that takes resources away from memory and thinking." But myelination loss, according to new research, should come with an asterisk. Most of it seems to occur on one specific part of neurons—the part responsible for learning new things. The part responsible for long-term memory shows no such loss.
In fact, a study of rhesus monkeys published this month shows how well the aging brain holds up. The animals’ prefrontal cortex indeed loses "dendritic spines," tiny protrusions that, acting as the brain’s wide receivers, catch the neurotransmitters that carry signals from other neurons. But there are two kinds of spines in monkeys as well as people. Small, thin ones are responsible for learning and remembering new things (where did I park my car?), and short, stubby ones are responsible for recalling things we’ve known for years. The brain loses some 45 percent of the first kind—and zero of the second kind, Morrison and colleagues reported in June in the Journal of Neuroscience.
That would account for why we have trouble with new memories as we age but not with our core knowledge. "We hypothesize that expertise and knowledge are coded in the synapses and spines that are not lost with age," says Morrison. "This may be how the brain retains what it learned decades ago, and why a professor of cell biology can teach well into his 80s." It may also be why, although most people’s ability to reason and solve novel problems declines with age, knowledge holds up just fine, with vocabulary increasing through at least age 60. Emotional intelligence, social skills, and self-control generally improve with age, too.
And as always, individuals differ. In general, cognitive processes such as processing speed—how quickly the brain takes in and makes sense of information from the outside world, as well as how quickly signals propagate along a thinking circuit—decline beginning in our 20s, just as our respiratory and immune systems decline. Memory and problem-solving improve into our 20s and then plateau, beginning to decline in our 50s or 60s. But averages hide big individual differences. The scores of some adults in their 60s on memory, problem--solving, and other cognitive tests are above the average of adults in their 20s. As anecdotal evidence, Salt-house gestures down the hall to the office of economist Robert Solow, 86, a Nobel laureate who is as intellectually active as ever and producing research papers that—and I’m going to have to just quote here—"rejected the representative-agent models that more or less impose optimal properties on ob-served trajectories" in macroeconomics.
We can’t all be Solows, even in our 30s—let alone our 80s. But clearly, some brains hold up better than others. Some of the difference may be genetic, but since we can’t go back and ask Mom and Dad to bequeath us different genes, the possibilities for intervention on this front are limited. That leaves how we live our lives. Salt-house points out that only about 20 percent of the variation among people in standard measures of memory, problem-solving, and other executive functions is the result of age. The rest—64 to 96 percent on different cognitive test scores, he estimates in his new book, Major Issues in Cognitive Aging—reflects factors other than age.
One such factor may be generational. Many of the dismal conclusions about aging come from what are called cross-sectional comparisons: haul 20-somethings and 60- to 80-somethings into the lab, test, compare, repeat. The differences are supposed to indicate what will happen to the first group when they reach the age of the second. But that may not be right. Consider a visitor to Miami. She notices that most of the older people are New York Jews, while many of the younger ones are Latino. She concludes that as people age, they change from Latino to Jewish.
We may be making a similar mistake when we compare young and old brains. The differences may not mean that mental function falls off a cliff as we age. Instead, warns Salt-house, many "age-related differences [in brain function] could reflect generational differences." The fact that more recent generations outperform older ones belies the idea that we are getting dumber, and is so well established, it has its own name—the Flynn effect. As a result, cross-sectional studies finding that today’s 80-year-olds don’t think and remember as well as today’s 30-year-olds may be capturing this generational difference, and thus painting a more pessimistic picture of the aging brain than it warranted. When the same people are measured over and over, says Salthouse, "at least before about age 60" there is "either stability or an increase" in brain function with age.
The recognition that so much of the difference in brain function is due to something other than age has ignited a market in interventions that might postpone, mitigate, or even prevent some of the decline. The largest study of interventions is ACTIVE (Advanced Cognitive Training for Independent and Vital Elderly), which began in 1998. It gave 2,832 adults, ages 65 to 94, either no training (the control group) or training in reasoning, memory, and processing speed in 10 sessions of 60 to 75 minutes each. The reasoning training, for instance, gave people strategies for breaking a problem into easier steps and identifying patterns of relations. The memory training involved strategies to form images or associations: to remember a list of words that includes penguin, scissors, and cupcake, for instance, visualize the bird wielding the tool while pecking the chocolate frosting.
As expected, people got better at what they trained on. In general, the gains were equal to turning back the clock seven to 15 years for reasoning and remembering, and even longer for processing speed. But there was essentially no transfer: getting better at memory did not sharpen reasoning, and faster processing speeds did not improve memory. Somewhat alarming was that after training, most people’s performance fell even more precipitously than it did without training. That probably reflects the fact that for brain training to "take," it has to be like aerobics, says Mahncke: "We think that for each core mental ability you want to train, you’ll need a booster every nine to 12 months."
Doing crossword puzzles would seem to be ideal brain exercise since avid puzzlers do them daily and say it keeps them mentally sharp, especially with vocabulary and memory. But this may be confusing cause and effect. It is mostly people who are good at figuring out "Dole’s running mate" who do crosswords regularly; those who aren’t, don’t. In a recent study, Salt-house and colleagues found "no evidence" that people who do crosswords have "a slower rate of age-related decline in reasoning." As he put it in a 2006 analysis, there is "little scientific evidence that engagement in mentally stimulating activities alters the rate of mental aging," an idea that is "more of an optimistic hope than an empirical reality." (P.S.: Bob Dole’s 1996 VP choice was Jack Kemp.)
What does support mental acuity as we age is the same thing that’s good for your heart, lungs, immune system, and muscles: aerobic exercise such as brisk walking. A seminal study by scientists at the University of Illinois found that three vigorous, 40-minute walks a week over six months improves memory and reasoning. It also spurs the birth of new brain neurons, scientists led by the University of Illinois’s Art Kramer reported in 2006, and increases the volume of white matter, which connects neurons, in areas responsible for such executive functions as planning.
Walking is free, but Americans spent $13 million on brain-fitness software and games last year, Ambient Insight, a market-research company, reported in April. Nintendo’s Brain Age ($19.99), the Web-based MyBrainTrainer ($29.95 for one year), HappyNeuron’s Brain Fitness ($69.95), and the like improve the skills they train, say independent scientists: drilling yourself to hit the right-arrow key when you see a green light improves reaction time, doing exercises in which you decide whether one face matches another will speed up visual processing, and determining whether words in a new list match any of those in an old one boosts short-term memory. But as in the ACTIVE study, it’s not clear these improvements translate into a fitter brain overall.
An approach that targets the underlying brain processes might. A computer-game-like program from Posit called InSight ($395), for instance, includes an exercise in which you discern which direction a pattern on a screen is moving as a second pattern appears before the brain is finished processing the first. The idea is to turn up the signal and dial down the noise in the brain. "We think it’s important to fix the underlying information-processing machine rather than target higher-level functions like memory directly," says Mahncke. "By training the brain to improve its signal-to-noise ratio, information goes through more accurately and faster." A 2009 study found that healthy older adults (65 and over) who used a Posit program based on the same principle, Brain Fitness ($395), an hour per day for eight weeks improved their processing speed to that of 40-year-olds and their memory to that of brains 10 years younger. And a study scheduled for publication finds that such "perceptual training" improves memory in older adults. It’s enough to give you hopethat, for the brain, aging may become almost optional.