Memory gets most of the attention, but executive function is another part of thinking affected by aging.
Most of us realize that our brains aren't miraculously immune from the aging process. Along with creakier knees and thinner hair, we expect some forgetfulness. More often than not, forgotten names and other lapses can be ascribed to normal age-related memory loss (subtext: "don't worry, it's not Alzheimer's disease.") And there are some tried-and-true ways to compensate for these mental glitches (more on that below).
We worry a lot about memory loss and, understandably, it gets a lot of attention from doctors and researchers. But age-related changes in our brains also affect other cognitive processes. One of the most important is executive function, an umbrella term for the complex thinking required to make choices, plan, initiate action, and inhibit impulses. Executive function affects everything from walking speed and attention spans to friendships and family ties (as some inhibition is necessary for socially appropriate behavior). Not surprisingly, studies have shown that executive function is more important than many kinds of memory for managing the day-to-day tasks of independent living. In addition, diminished executive function in older people seems to be associated with a higher risk for falling, and a fall is often a calamitous event for an older person, ushering in ill health and disability.
Compared with all that has been written about memory, the advice on preventing and coping with the loss of executive function is pretty short. Children with attention deficit hyperactivity disorder (ADHD) have poor executive function, and researchers have studied whether methylphenidate (Ritalin, Concerta), the drug that's most commonly used to treat ADHD, might help older people with executive function deficits. The results have been mixed, so pharmacology may have some answers, but it doesn't look like it will produce a quick fix. (If you are interested in these studies, we've put some of the details on our Web site at www.harvard.health.edu/healthextra; look for the March 2010 issue.)
The good, if not terribly exciting, news is that the dos and don'ts of preserving executive function include many of the common precepts for staying healthy. For example, the to-do list once again includes exercise, as the evidence that older minds benefit from busier bodies continues to grow. A number of randomized controlled trials have shown that older people who exercise have better executive function than those who remain idle, and aerobic exercise (the kind that gets your heart going) may be especially beneficial. Results from a small study (33 people) published in Archives of Neurology in January 2010 showed that a fairly intense aerobic exercise program (four 45- to 60-minute sessions per week) improved the executive function of women with mild cognitive impairment. (The men weren't so fortunate.)
That familiar nemesis, high blood pressure, affects both memory and executive function, but it seems to have a more pronounced effect on the latter. The road to blood pressure control is well-marked, if sometimes difficult to travel: lose weight, eat more fruit and vegetables, cut back on sodium. People often end up taking a blood pressure–lowering medication.
Lack of sleep scrambles many cognitive functions, including executive function, so you can probably add maintenance of executive functioning to the long list of reasons for getting good sleep regularly.
The boss of our thoughts
Executive function has been compared to the conductor of a symphony orchestra. The term represents the brain's system for organizing and integrating other cognitive processes the way a conductor gets musicians to play together. That's an imperfect analogy (most are), and comparisons to other authority figures — a boss, a coach, a director — might work just as well. The underlying notion is the same regardless. Executive function can be viewed as the higher-order tasks that impose some order on our unruly mental lives — the thoughts that keep the cognitive underlings in line.
When it comes to actually defining executive function, every researcher and textbook seems to do it a bit differently, but the ability to plan is almost always mentioned. Planning requires a whole set of interlocking cognitive tasks. You have to set a goal, direct attention to the task at hand while ignoring others, modulate behaviors so constructive action can take place, and control impulses that would otherwise get in the way of those constructive behaviors — and that's just a partial list. Poor executive functioning may result from a deficit in any one of these areas. And while it's useful for some purposes to tease memory and executive function apart, there's also considerable overlap between them. It's clear, for example, that some working memory — holding information "on line" for a short time — is necessary for us to plan. Memory and the ability to envision future events, a component of planning, are related. Results of a study published in 2009 showed that people with Alzheimer's have trouble imagining future events, in addition to remembering past ones.
Some authors argue that executive function is an evolutionary advantage that allows higher organisms — particularly human beings — to take in new information, consider it, and choose from several available options, rather than depending on innate drives and reflexes. Another way to put it is that executive function allows us to decide rather than just react.
Researchers believe the area of the brain most involved in executive function is the prefrontal cortex, which, as the name suggests, is in the forefront of the brain. The prefrontal cortex includes the anterior cingulate gyrus, which has been associated with attention and response to stimulation, and the ventral prefrontal cortex, which has been associated with inhibition and social appropriateness. However, mapping executive function to only certain areas of the brain oversimplifies matters, because a complicated process like executive function depends on a network of connections to many other parts of the brain. Moreover, brain anatomy and function aren't hard-wired. If one part of the brain isn't functioning properly, another part can take over.
Dementia and executive function
Dementia is a word that gets tossed around a lot. It's often equated with Alzheimer's disease, when, in fact, there are several disorders (Lewy body disease, frontotemporal lobar degeneration) that harm brain tissue differently than Alzheimer's does but also result in dementia. Moreover, many cases of dementia are vascular in origin: small areas of the brain die, are damaged, or don't function properly because of inadequate blood flow from damaged or blocked blood vessels. To further complicate matters, the various causes of dementia often overlap, so, for example, people may have dementia from a mixture of Alzheimer's disease and vascular deficits.
When dementia is being used to describe a state of mind and not the disease that is causing it, the term is sometimes used interchangeably for memory impairment. But that's an oversimplification. According to the strict psychiatric definition, memory impairment is just one element, and a diagnosis of dementia requires memory impairment and at least one other cognitive "disturbance": aphasia (impaired ability to use language), apraxia (impaired ability to perform simple movements despite having intact motor abilities), agnosia (failure to recognize familiar objects), or poor executive function.
In this definition, the memory impairment part of dementia affects the ability to learn new information, to recall previously "stored" information, or both. Executive function is said to require abstract thinking and to entail the ability to plan, initiate, and sequence behavior. So it's easy to see how memory impairment would make good executive functioning very difficult, if not impossible. If you can't gather or hold on to information, it's hard to make a plan and maybe even harder to follow through on it.
Executive function isn't a new concept, but researchers are beginning to make a point of considering it separately as they design studies and analyze data. This is particularly true for investigations into aging and cognitive function. Two examples published in 2009 were based on data collected for MOBILIZE Boston, a study of the risk factors for mobility and falls in older people (average age 78) that is funded by the National Institute on Aging and based at Hebrew SeniorLife, a Harvard-affiliated long-term care provider in Boston.
The first study compared people's physical activity levels, as measured by a standardized questionnaire, with their scores on a battery of tests designed to measure different aspects of thinking. Statistical adjustments were made for age, sex, education, and cardiovascular disease. Right in line with results from other studies, the researchers found that people who were more active were also more likely to have well-preserved executive function. But when they looked at the tests for memory, they didn't find a correlation between high scores and physical activity. Their tentative conclusion: physical activity has a specific biological benefit for executive function that it might not have for memory.
The second study used a statistical technique called latent class analysis that groups people into clusters based on whether they share some predetermined attributes. In this case, the researchers — most of whom are affiliated with Harvard — examined the results of brief tests that measure memory, executive function, walking speed, and depression. After crunching the numbers for about 580 participants in the MOBILIZE Boston study, they identified a cluster of 99 — about one in six people in the analysis — who shared three attributes: a very slow gait, depression, and poor executive function. Notably, memory deficits were not included. When the researchers dug a little further, they found that some of the classic cardiovascular risk factors — high blood pressure, diabetes — were associated with being a member of this low-performing group. They speculated that the triad of slow gait, depression, and poor executive function is a manifestation of a brain suffering from "vascular aging" — the slow accumulation of minor damage to the small arteries that supply the brain. Moreover, this vascular aging may have a specific effect on the part of the brain that controls executive function. This is the flip side to the first research group's inference that physical activity might have special benefits for executive function.
Ways to improve your executive function
We've already mentioned the research that suggests that exercise, blood pressure, and sleep seem to have an effect on our inner CEOs. Avoiding excess stress and alcohol could probably be added to the list. These are generic, all-purpose risk factors, invoked over and over again, partly because doing so plays into the belief that we, as individuals, have some power to change them.
But is there anything more specific we can do for executive function? After all, millions of words have been written and spoken about techniques for preserving and improving memory. The standard advice includes building associations between new information and older memories and chunking information. We've posted descriptions of some of these techniques on our Web site.
In contrast, precious little has been said about keeping our executive functioning sharp. However, some of the common suggestions for memory preservation and enhancement are very much related to executive function and its various components. Here are a few examples:
Pay attention to paying attention. A common memory tip is to work on maintaining focus, because as we age, new information doesn't seem to get "into" our memories as easily as it did when we were young and our brains spongier. Attention is a central part of executive function, so this memory advice is, in effect, asking us to dial up our executive functioning.
Say it out loud. Saying things out loud is another standard memory tip ("I am now putting my keys in my pocket"). Doing so encourages a person to pause and pay attention to what he or she is doing.
Make it a habit. Memory books typically suggest putting keys and other personal items in the same place so you don't have to remember where you put them. That suggestion, plus others to reduce clutter and work on organizational systems, can be seen as ways of reducing demands on executive functioning. If the keys are always in the same place, we know automatically where they are and don't have to get executive functioning involved to find them.
Write it down. Lists and plans of action are a way of "outsourcing" executive function from the brain to a piece of paper or a computer file. We may need executive function to create these lists, but having them recorded elsewhere allows us to go on autopilot a little bit, instead of redeciding everything over and over again.