Successful Aging: A Neuroscientist Explores the Power and Potential of Our Lives

by Daniel J. Levitin

Perceptual completion emerges in infancy between around four and eight months, and adult-like adjustments come at around age five. A more everyday example of perceptual completion involves the blind spot in our visual field. In the part of the retina where the optic nerve passes through, there are no cones and rods, and so no visual image is projected there—and yet our brains fill in the missing information based on what surrounds it.

There is a trend, as we age, to get better and better at this sort of perceptual completion, precisely because we have experienced so much more of the world that our mental database of what is likely and what is unlikely is informed by millions more observations. These observations become data for the (unconscious) statistical processor of our brains. Through neuroplasticity, this changes the wiring of our brains with each new observation. So even though our sensory receptors begin to show wear as we age, and our brains show atrophy, decreased blood flow, and other deficits, our perceptual completion can improve. This is another of the many compensatory mechanisms that bring an advantage to the aging brain. Older people may well be more efficient and accurate at dealing with degraded signals than young people, because their perceptual system has more experience with the world.

Airplane pilots spend dozens of hours learning not to place too much emphasis on their visual system, or, for that matter, on their vestibular system, and instead to “trust the gauges.” Our brains and bodies have not had time to evolve systems for accurately interpreting the sensations that come from being in flight, and so they can be unreliable. Many fatal accidents have occurred from pilots ignoring their gauges and instead relying on their perceptions.

John F. Kennedy Jr. Flying at dusk in poor weather, he may have been unable to distinguish the sky from the water he was flying above and he may have had the bodily and visual sensation that he was upside down. His gauges would have told him whether this was true or not, but he may have thought that the gauges were malfunctioning—this happens occasionally, but less often than our senses mislead us. It seems he turned the plane upside down and flew into the water, thinking he was ascending into the sky. This is also believed to be what is responsible for aviation accidents in the Bermuda Triangle—pilots become disoriented with no landmarks, they confuse the air and the sea, and while ignoring their gauges but trusting their (unreliable) senses, they fly their planes right into the deep.

This change in vision is called presbyopia. It occurs because of age-related changes in proteins in the lens, making the lens harder and less elastic over time. Age-related changes also take place in the muscle fibers surrounding the lens. With less elasticity, the eye has a harder time focusing up close, which takes more muscle tension than focusing far away.

evolution is dependent on reproduction to transmit survival advantages across multiple generations. Consequently, evolution does not generate adaptive improvements for conditions that occur outside of normal reproductive age. Hence, there has been no evolutionary pressure to favor people who don’t get cataracts or presbyopia, and so they are ever present in aging populations.

With age, the touch sensors in the pads of the fingers deteriorate, producing a loss of sensitivity. We fumble with things. Arthritis makes it painful to move our fingers and toes. As Atul Gawande writes, “Loss of motor neurons in the cortex leads to losses of dexterity. Handwriting degrades. Hand speed and vibration sense decline. Using a standard mobile phone, with its tiny buttons and touch screen display, becomes increasingly unmanageable.”

a common affliction of old age that is going to sound made-up but is real: a patch of skin on your back, typically just out of reach, that itches intermittently, and sometimes incessantly. And scratching it provides no relief—none at all! Because the condition arises from damage within certain nerve pathways, those same pathways block the relief that scratching usually provides. The condition is called notalgia paresthetica.

Women generally have a more refined sense of smell than men and can detect odors that men can’t, thanks to having a larger concentration of olfactory neurons. In

The pleasurable feelings from eating tasty food become more important in old age when other sources of sensory gratification—like physical contact—may have become compromised or are less frequent.

we can detect four tastes: sour, salty, sweet, and bitter. Taste scientists (yes, there is such a thing) identified a fifth taste, umami, which detects the presence of an amino acid, glutamic acid, that is typically described as a meaty or brothy taste. We encounter it in meats, fish, mushrooms, and soy sauce, and it is also present in breast milk in about the same proportion as in soup broths.

Many older adults complain that food lacks flavor. This is usually due to olfactory deficits—smell works in tandem with taste to convey the flavor of food and drink, and sensors inside the cheeks feed into the brain’s olfactory centers. Other causes of taste deficit are a history of upper respiratory infections, head injury, drug use, and an age-related reduction in saliva production. All of these factors can cause loss of appetite, loss of pleasure from eating, malnutrition, and even depression.

The most noticeable problem in taste perception affecting older adults is an upward change in thresholds—it takes more of a given flavor to be perceived as the same amount as before. For a typical older individual, with one or more medical conditions and taking three prescription medications, the number of flavor molecules required to detect a taste shows marked increases depending on the flavor. If you’re typical, you’ll need to have a whopping twelve times the amount of salt to detect that salt is even present compared to when you were in your fifties. For bitter tastes, such as quinine, seven times the amount; for the brothy-meaty flavor of umami, five times the amount; and for sweeteners, around three times the normal amount.

People age at different rates. Within the life span that you will have, the goal is to try to increase your health span and decrease your disease span

The wisdom that we find in older adults—the most experienced members of our population—follows from these four specific things: associations, experience, pattern recognition, and the use of analogies. And this is why we gain more and more wisdom as we age. Wisdom comes from the accumulated set of things we’ve seen and experienced, our ability to detect patterns in those experiences, and our ability to predict future outcomes based on them. (And what is intelligence if not that?) Naturally, the more you’ve experienced, the more wisdom you are able to tap into. In addition, certain changes in the aging brain facilitate these kinds of comparisons.

Starting in the early 1900s, psychometricians and cognitive psychologists—the folks who measure and study intelligence—thought of intelligence as a single, unitary thing. It varied along a single continuum and you could have more or less of it, whatever it was. Their measurement of it was called the intelligence quotient, or IQ.

Even though humans all share basic genetics and neuroanatomy, developmental stages, and hormonal changes, each of these is shaped by the individual’s particular experiences.

Scientists call the things you’ve already learned crystallized intelligence, and they call your potential to learn fluid intelligence. There’s also a third intelligence I call acquisitional intelligence—that’s the speed and ease with which you can acquire new information (if given the right opportunity).

Crystallized intelligence is the knowledge you have already acquired, regardless of how easy or difficult it was for you to obtain it. It includes things such as your vocabulary, your general knowledge, your skills, and any mathematical rules or formulas you might have learned. It is heavily dependent on culture, because certain kinds of knowledge are valued more than others depending on where you live. Think knowledge of plants for people living in a hunter-gatherer community versus reading for people living in an industrialized community. Crystallized intelligence also depends on educational experience and opportunity.

Fluid intelligence is your ability to apply any information you have (whether it’s extensive or not) to new contexts. It is your innate ability to reason, to think, to identify patterns, and to solve problems.

Many cognitive scientists believe that the more expertise one obtains in a given domain, the larger the gap between that domain and others. (An exception would be polymaths, such as Leonardo da Vinci.)

exceptionally high-performing individuals. They tend to excel in a single domain, or perhaps two. It’s not that they couldn’t excel in many; it’s that as these high performers start to get really good at something, they become increasingly absorbed in it and continue to develop that single area of expertise by redirecting brain resources toward it, letting other areas that are less relevant to them fall by the wayside.

the best strategy for cognitive health is to keep doing new things—things that require new ways of thinking. If you never did crosswords before and you start at seventy, that’s great. If you’ve been doing crosswords since you were sixteen, there’s no reason to stop now, but don’t expect them to be a magic elixir that fends off dementia. Instead, find some other kind of puzzle you’ve never done—a Rubik’s cube, logic problems, jigsaw puzzles, 3-D wooden jigsaw puzzles, brain teasers. They can be frustrating at first, so it’s best to start easy. And stick with it.

aging brain and reaction times: The number to remember is 1⁄25th of a second, which is the annual decrement in reaction time that we found in participants between the ages of 30 and 71 years.

Processing speed and prefrontal cortex function are significantly correlated. The prefrontal cortex is responsible for a number of aspects of cognition that often decline as we age: inhibiting distracting or irrelevant information planning, scheduling analytical thinking executing complex, sequential motor actions handling novelty fluid intelligence

the prefrontal cortex is susceptible to age-related decreases in blood flow, changes in the structure of cells, and reduction of volume (shrinkage). A biological explanation is that there is no evolutionary pressure for the prefrontal cortex to stay sharp in old age, just as there is no evolutionary pressure for anything to stay sharp in old age. (Once we are past the age of reproducing and passing our genes to the next generation, evolution doesn’t care about how we spend the rest of our lives.) And so processing speed, led by prefrontal cortex decline, slows down.

low fluid intelligence in childhood predicted greater depressive symptoms in old age. High fluid intelligence is protective against the declines of aging, not just intellectual declines but emotional ones as well.

Practical intelligence increases with age, peaking after age fifty or sixty.

Analytical intelligence is preserved in old age if you can practice using it. Rather than passively taking in information, question it, relate it to other things you know, and ponder it.

People who retire fade rather fast unless they have something really important they want to do. It’s feeling that you have purpose, and that you have less and less time to make your mark. Instead of slowing down you have to speed up.

Abstract thinking occurs in higher brain centers; it isn’t unique to humans but is most fully developed in our species, and it underlies mathematical ability, language, problem solving, and industrialization. Intelligent, adaptive behavior requires abstracting behaviorally relevant concepts and categories, an ability that gets better with age.

The developmental trend toward abstract thinking is one of the compensatory mechanisms of aging that mitigates the decline of our sensory systems. Even apart from that decline, the trend toward abstract thinking helps us to solve problems that would not be solvable otherwise. Aging is not accompanied by unavoidable cognitive decline. The aging brain changes, thanks to neuroplasticity. It changes itself, heals itself, and finds other ways to do things, some of them (such as abstract reasoning) actually better than the earlier ways of doing things; it harnesses neuroprotective and neurorestorative capabilities.

The ability to learn new things quickly reaches a peak in adolescence and the college years and declines after age forty. Fluid intelligence, the ability to use what we already know, is lower before the age of forty and picks up in each decade thereafter. Although our raw neural processing speed and reaction times may slow down (precipitously in our eighties), older adults have experienced so much more than twenty-year-olds that they have a competitive edge.

The rate at which our cognitive abilities decline, and the severity with which we might develop dementia, are all highly variable. Many individuals (in some reports up to 25 percent) show the biological, pathological markers for Alzheimer’s disease and yet show zero impairment in thinking capacity. Cognitive reserve can insulate against the damaging effects of aging. So how do you get cognitive reserve? High levels of education and a balanced diet help.

Developmental psychologist Judith Glück proposes that life challenges act as catalysts for the development of wisdom, and our internal resources influence how we appraise, deal with, and integrate these challenges. According to her model, the internal resources that predict the development of wisdom include: mastery (managing uncertainty and uncontrollability), openness, reflectivity, and emotion regulation, including empathy (the model is called MORE). External resources are equally important. Other people, such as friends and mentors, play a crucial role in both the short-term expression and the long-term development of wisdom. Situational contexts, including life phases, also influence the extent to which people act on their wisdom-related knowledge.

The wisdom we attribute to older adults may well be neurobiologically based, born out of changes to the brain that allow the two hemispheres to communicate more freely, to combine the logical with the intuitive, the quantitative with the qualitative, the fact-based thinking with the artistic. Greater wisdom is also marked by freer connections between the frontal lobes and the much older limbic system, and by age-related changes in neurochemistry.

not everyone grows wise with age. Wisdom comes from combining motivational, emotional, and cognitive experiences, having successfully overcome challenges, and having had meaningful interactions with others. Although we may think of wisdom as primarily an intellectual quality, in fact it is heavily reliant on emotional maturity and a shift in those motivations that drive us. Emotion and motivation change with age as a function of a number of different hormonal and neurotransmitter changes in the brain.

Emotions arise inside of us and profoundly affect our moods. What are these psychological states exactly? Emotions are related to moods, but they’re not the same thing. Emotions are an acute state of affect and arousal lasting from seconds to minutes, whereas mood refers to a longer-term emotional tone. Emotions occur against a background of mood. You might be in a slightly irritated mood after having had an argument with your boss. Then, when someone steps on your foot in line at a Starbucks, or your seven-year-old keeps interrupting you, well, that’s when you begin to exhibit emotion.

No one is claiming that animals don’t experience emotions—they clearly do—but they probably experience them differently because they lack the cognitive analytic tools to interpret them in the complex ways that we do.

there are emotions that dogs and other animals appear to lack completely. For example, my dog, Madeleine, although we often think of her as human, does not experience disgust. Neither did the succession of best friends who preceded her: Winifred, Shadow, Isabella, Charlotte, Karma, or 99. Dogs will eat or roll in practically anything and show no evidence of the emotion of disgust, which appears to be uniquely human. As infants, we don’t have it until we’re three to seven years old, but once we get it, we hang on to it for life. In fact, the older we get, the wider our experience of disgust becomes, as we contemplate injustice, violence, and fraud in our world—not just excrement or rotten food.

Emotions also promote social currency, the understanding of others’ mental states. To do this, your brain makes emotional inferences.

when it comes to the emotional interpretation of events, your brain is making not predictions but superfast “postdictions,” after-the-fact inferences about things that have already happened. Your brain is continually rewriting your perceptual history to conform to new incoming facts. This is a form of Bayesian inferencing: form an opinion and update that opinion as new information becomes available.

Stress is also an emotion, one that we share with other animals and with one another across the life span, although the causes of stress can be quite variable. Chronic stress is especially harmful. Stress is also highly variable—what would stress out one person another takes in stride, and vice versa. Stress can have a substantial impact on longevity.

homeostasis, the idea that the body seeks to maintain consistency, say, in core temperature, or blood levels of oxygen. In the last twenty years, though, we’ve recognized that levels of some of our physiological systems—such as blood sugar levels, heart rate, blood pressure, and respiration rate—require continual adjustment to function optimally. This idea of stability through change is called allostasis—systems fluctuating regularly in response to life’s demands.

When a situation is perceived as being stressful (because it is novel, unpredictable, uncontrollable, or painful), two major classes of stress hormones are secreted, catecholamines and glucocorticoids. They are the first hormonal systems to respond to stress. The short-term secretion of these hormones in the face of a challenge serves an adaptive purpose and leads to the fight-or-flight response (allostasis). However, the same stress hormones that are essential for survival can have damaging effects on both physical and mental health if they are secreted over a longer period of time (called allostatic load). This happens because when these primary stress hormones are increased for long periods of time, it leads to dysregulation of other major biological pathways in the body and the brain, for example, insulin, glucose, lipids, and neurotransmitters. This in turn causes a dysregulation of various other operations, such as the immune system, the digestive system, the reproductive system, cardiac health, and mental health.

Your allostatic load is the cumulative effect of stress over time; it indexes your changes in various biomarkers of stress (blood sugar, insulin, immune markers, stress markers, etc.) in response to the events of your life. Your allostatic load can be calculated by looking at levels of certain “stress biomarkers,” including C-reactive protein, insulin, blood pressure, and so on. Social support i...

Because allostasis is a predictive system, it can be influenced or miscalibrated by early life stressors or extreme traumas. A stable fetal and early childhood environment can lead to a well-functioning allostatic system. But adverse childhood experiences can result in a system that either overreacts or just shuts down in response to what might otherwise be considered normal daily ups and downs, creating hypervigilance, reduced resilience, and sometimes wild mood swings—a lifetime in which normal allostatic regulation is never reached.

Elevated cortisol levels in response to early life stress have been linked to accelerated hippocampal atrophy among both healthy individuals and people in the early stages of Alzheimer’s disease. Thus, successful emotion regulation may protect not only older people’s physical well-being but their mental capacities as well.

not everyone with a stressful childhood ends up with a psychiatric disorder, or even a high allostatic load. Stressful experiences can lead to very different outcomes, depending on the interaction of the factors listed above. Some people develop resilience, grit, tenacity, and focus. Others fall apart. The prized combination that allows some people to live more positive lives, to turn lemons into lemonade, is still unknown and an active topic of research. One thing we do know is that thoughtful parenting and/or education can put people on the more positive path and give them better overall life outcomes, reducing the disadvantages caused by childhood adversity.

Because allostatic load is defined as the cumulative effects of stress and your body’s responses to that stress, the load and associated cellular damage increase with age, no matter how well-functioning the system is. In particular, normal age-related changes in structures that regulate allostasis, the hippocampus and the prefrontal cortex, make healthy allostasis more difficult to maintain. Higher load has also been associated with reductions in the brain’s gray matter. Three recent studies have also linked sleep disturbances to increases in load.