Читать книгу Brain Rules for Aging Well - John Medina - Страница 15
ОглавлениеWrinkles should merely indicate where smiles have been.
—Mark Twain
Happiness is nothing more than good health and a bad memory.
—Albert Schweitzer
A BIRTHDAY CARD RECENTLY caught my eye: “Grumpy Old Man To-Do List.”
1. Tell kids to get off MY lawn.
2. Scowl at the neighbor.
3. Write SCATHING letter.
4. Disinherit somebody.
5. Go for a long SLOW drive in the passing lane and keep signal on the whole time.
6. Tell kids to get off my lawn AGAIN!
7. Buy more NO TRESPASSING signs!
8. Tell some punk that in my day we had it tough.
9. Grumble grumpily for a while.
You open the card and it says:
10. Have a Happy Birthday!
As this card suggests, with many all-capped letters, older people have a reputation for being grumpy. Is this reputation warranted? Seniors also have a reputation for being kindly, patient, and wise—words not usually associated with grumpiness. That was certainly my experience with my grandparents. From a research point of view, these questions have serious definitional issues. What does happiness even mean? While researchers don’t unanimously agree on definitions, I am going to go with research psychologist Ed Diener, who defines happiness as “subjective well-being.” And with legendary researcher Martin Seligman, who defines optimism as knowing that bad things don’t last forever, that good will return. One is a condition of the present, and the other is an attitude about the future; both perspectives seem useful. As we’ll see, our thirst for optimistic experiences—and our ability to recall them—grow more robust as the years go by.
Onward, mostly upward
Confusion reigned for the longest time about whether people got grumpier or happier or just stayed themselves as they aged. Some studies found that people really fit Beatrix Potter’s classic “grumpy gardener Mr. McGregor” stereotype: they got crankier as they got older. Perhaps this was because the seniors studied lived in an environment of unrelenting arthritis, unrelenting funerals, and unrelenting loneliness. Other studies seemed to show the opposite. People became happier and better adjusted as they aged, becoming the type of sage that actor Morgan Freeman often plays in shows like The Story of God. Perhaps this was because they lived in a world of increasing wisdom, found a way to avoid more heartaches, and became more socially enriched as they shared their insights. Which is it, folks, Beatrix Potter or The Story of God?
Happily, further research provided a clearer picture, and much of it is positive. People really do become happier as they age, but with one important caveat about depression, as I’ll explain shortly. They develop more emotional stability, become more agreeable, are more conscientious. The difference is not small. To take just one psychometric measure, people in their sixties score 69 percent higher than people in their twenties on emotional stability assessments. Seniors score even higher on agreeableness tests.
Why the historical discrepancy? It’s a classic error. Most of the older studies did not take into account the environmental life experiences of those they examined. This includes controlling for what we now call the usual socioeconomic suspects: wealth, gender, race, mood, education, job stability—even year of birth. Seniors born in the Great Depression, for example, don’t have the same happiness profiles (a chart of the years they tended to be most and least happy) as baby boomers, and both have profiles different from millennials’. Whether you have children is a factor, too. Marital satisfaction, which profoundly influences happiness assessments, ebbs and flows depending on the age of the kids you are raising. Marital happiness is highest when the kids are gone, by the way—in the stretch of life between empty nest and retirement. It’s lowest when the kids are teens.
When you wade into the deep end of the statistical pool and take some of these factors into account (as was done in one National Institute on Aging study, which looked at several thousand people born between 1885 and 1980), a clear upward trend toward happiness emerges. As one journal put it, “Well-being increases over everyone’s lifetime” (emphasis mine). Another study taking into account similar variables—this one involving more than fifteen hundred people ages twenty-one to ninety-nine—also found that people aged on a positive note. And if that were the end of the story, we could just whistle a happy tune, pack up our bags, and end this chapter. Turns out not everything about mood improves, and the boost does not last forever—or for everybody. Before we get to that, however, we have to figure out why, for so many, it lasts so long.
What Satchmo says
One of the most relentlessly upbeat songs of the late 1960s and early ’70s rock era was performed not by a rock group but by a jazz legend. It was Louis Armstrong’s interpretation of “What a Wonderful World”:
I hear babies crying,
I watch them grow;
they’ll learn much more
than I’ll ever know.
Armstrong then marvels at what a wonderful world it is. Some people took exception to this half-full glass of rosy-colored water. With the Cold War in full flower and the Vietnam War in hideous bloom, the world could hardly be called wonderful, right? Armstrong heard about these criticisms, of course, and before graveling it out at a concert one night, he announced this to the audience:
Some of you young folks been saying to me: “Hey, Pops—what do you mean, what a wonderful world? How about all them wars all over the place, you call them wonderful?” But how about listening to old Pops for a minute? Seems to me it ain’t the world that’s so bad but what we’re doing to it, and all I’m saying is see what a wonderful world it would be if only we’d give it a chance. Love, baby—love. That’s the secret.
Remarkable, coming from a man whose greatness endured large helpings of Jim Crow, using bathrooms and drinking fountains marked “Colored Only.”
It is Life 101: we’ll experience both positive and negative events over time. The same generation that witnessed the My Lai massacre also watched a man land on the moon. As the years roll by, however, our brains don’t process positive and negative information in a balanced way. Our desire for (and memory of) optimistic input gets more intense as we age, and we begin to experience life more as a wonderful world.
How do we know? The surprising initial finding of scientists was that older people experienced fewer negative emotions than their younger counterparts. Researchers such as Mara Mather, gerontologist at USC, and Laura Carstensen, director of the Stanford Center on Longevity, decided to investigate. Consistently, they found that older people’s brains paid more attention to positive stimuli than negative stimuli. And seniors remembered more details about the optimistic stuff, too.
One experiment involved younger people (average age twenty-four) and older people (average age seventy-three) gazing at happy and sad faces. Which would they pay the most attention to (“attentional bias”)? When the youngsters looked at positive faces, they scored 5 out of 25 on the bias scale; they scored 3 out of 25 for negative faces. This meant they were paying modest, fairly balanced attention to each. When seniors looked at the same faces, they scored 15 out of 25 for positive faces and –12 of 25 (yes, negative 12) for the not-so-positive faces. Nothing modest or equal there.
Researchers observed similar differences when they assessed that most dissonant note of aging neurons—negative memories. To understand these data, we need briefly to review how memory works. (We’ll have a more full-throated treatment in the memory chapter.) The important concept is this: brains don’t record life as if on a single reel-to-reel tape deck. Rather, many semi-independent memory subsystems exist—many types of tape decks, if you will—each responsible for recording and retrieving a specific domain of learning. Learning how to ride a bicycle, for example, uses a different neural deck than remembering an episode of Breaking Bad or recalling that Tony Bennett sang “Put on a Happy Face.” Your ability to recognize something you’ve seen before (recognition memory) uses yet another memory subsystem.
To test recognition memory, both younger and older populations were shown pictures of “positive images” and “negative images” (such as a person making a happy or a sad face). Younger adults recalled both at roughly equal percentages. Not so for older adults. Their recognition scores were 106 percent higher for positive images than for negative ones.
Researchers have noticed analogous changes for episodic memory (memories for events), short-term memory (now called working memory), and long-term memory (just what it sounds like). The phenomenon even has a name: the Positivity Effect. One reason older people report being happier is that they’re increasingly selective about what they pay attention to—and what they remember when they do pay attention.
Why all this optimism in seniors? After all, their joints begin to ache for reasons that become increasingly untreatable, friends begin dying off as if in a war zone, they forget why they went downstairs, and they quit remembering your birthday. Happiness is probably one of the many rewards the brain uses to keep us pro-social. Emphasizing positivity keeps depression away, buffering against suicide. People who are more positive toward us are more likely to lend us a hand in our old age—useful for survival.
There’s another pro-social reason seniors are happier. To explain it, I’ll turn to an Industrial Age Brit who would not be caught dead putting on a happy face. We’re going to talk about that quintessential grumpy old man, Ebenezer Scrooge.
Lessons from London
The most unsettling aspect of Dickens’s A Christmas Carol to me is that some of its nineteenth-century pages seem lifted straight out of a twenty-first-century geroscience textbook. As proof, I offer you a few degrees of Ebenezer Scrooge’s famous narrative arc. He starts as a miser about Christmas, as you know, and doesn’t change to Santa Claus until he finally confronts his death. What helps turn him away from the dark side isn’t a grave marker, however. (Presumably death is as much a concern to innocent Tiny Tim as to greedy moneylenders.) The change agents come gradually, from the types of things Scrooge observes as the ghosts force-feed him his biography. When Scrooge is young, his mind is on his newly minted career, the knowledge-based world of industrial-age banking—and his increasingly self-centered success. But when he is old and the Spirits have held sway, his priorities have been turned upside down (or, rather, right side up). He exchanges the cold, knowledge-soaked world of accounts receivable for the warm, emotion-soaked earthiness of human relationships.
Here, data and Dickens meet, for this exchange—minus the ghosts—is exactly what happens to our brains with age. We, too, shift from paying off college debt and other financial priorities to playing with grandkids. This, on average, makes us happier. The delightful metamorphosis stems from both nurture and nature, each of which deserve a hearing.
In your youth, your brain fools you into believing you’ll live a long time, if not forever. This is an attitude positively shackled with social consequences—ranging from whether you commit to retirement savings or sign up for health care. (Insurance companies often call people in this age group “the immortals.”) You are also at the starting gate of your career, and so you see knowledge-based pursuits as your top priorities for future achievements. Ditto for your relational successes. Anyone who’s been married, had children, or experienced both understands how much extra knowledge you need to be successful.
All that changes with age. You now have a few more miles on your biological tires and greater knowledge about how the world works. You hardly need three ghosts to realize you were wrong and won’t live forever. I remember first discovering this when I wrote down the number of books I wanted to read before kicking the bucket. I calculated the time it would take to read them and realized I would need to live more than 180 years to finish. And that’s if I didn’t do anything else but read books. While that is surely a vision of heaven for me, I have, unfortunately, other things to do. Aging forced me to prioritize. And since I knew I wanted to spend more time with my family than with Dickens, or any other author, I could sense something warmly relational shifting beneath my behavioral feet.
This shifting is consistent with the research literature. When you truly realize you have a sell-by date, like the post-ghost Scrooge, you begin to prize relationships over just about everything else. And any time you prioritize the socioemotional components of life, you become happier—the entire point of the friendships chapter. This shift is so common, and is backed by so much empirical support, it’s been christened with its own tediously academic title: socioemotional selectivity theory.
At the same time scientists puzzled over the weight of these behavioral data, others began ruminating over their potential neurological origins. They came up with their own, arguably more disturbing, name for their findings: FADE, short for frontal-amygdalar age-related differences in emotion.
We’ve already discussed one of those differences: the more social relationships you acquire, the bigger the amygdala becomes. Other differences also accrue with age. Aging brains activate the appropriate emotions with greater strength—just as those emotions are changing the way we react to the world. It’s quite possible that the neurological effects termed FADE directly affect what we think is important. A lifetime of Christmas geese results.
Roller-coaster grandpa
Older people are supposed to be allergic to risk. Don’t tell that to Gary Coleman, a retired pastor from Ohio, however.
Looking something like the actor Sean Penn, if Sean Penn were seventy-four, Reverend Coleman is a roller-coaster fanatic. In 2015 he took his twelve thousandth spin on Ohio’s legendary Diamondback roller coaster. “I thought it was the best coaster I’ve ridden on my whole life,” he exclaimed in an interview. “At my age, it’s great!” He knows of what he speaks. He’s been riding roller coasters obsessively since childhood.
Researchers have found two interesting patterns concerning how risk-related behavior changes as people age, and they’re definitely related to happiness, just like the good reverend’s roller-coaster experience. One is called the “certainty effect,” the other “prevention motivation.”
The certainty research was initially hobbled by uncertainty. That’s because young and old are willing to take risks at roughly equal rates, and with roughly equal enthusiasms. Knowing that equality doesn’t always mean similarity, however, the researchers put their heads down and charged straight at their spreadsheets. That’s when they smashed into something solid. The kinds of risks the generations take are as different as a noisy casino is from a cozy teahouse.
If you are of a certain age and find yourself feeling risk averse these days, you’re not alone. When given a choice between larger potential gains with substantial risk, or smaller potential gains with smaller risk, seniors almost always choose the smaller gain. In fact, risk aversion is always largest if there’s a threat of losing a potential reward, however small that reward might seem. Why? Seniors prefer the higher probability of experiencing a positive emotion. Like with operating the penny slots, reward size doesn’t matter to seniors, as long as they can play. This finding is so common, researchers call it the certainty effect.
Contrast this easy satisfaction with our younger selves. In youth, the altitude of happiness we experience is consistently stratospheric, and we want more. We crave a dance, a rave, loud music, louder friends. After all, we might find a lifelong mate in these vigorous activities or, later, potential connections for work advancement. It’s a risky way to play at life, given the stakes, and aggressively self-serving. But it’s also understandable. In our youth, our emphasis is on the future, not the past—perhaps because we haven’t made one yet. Which is why staying home and watching reruns of I Love Lucy is not exactly our idea of a good time. The researchers who quantified this preference named it “promotion motivation.”
Reaping the consequences of promotion motivation, we then swear fealty to the iron thrones of mortgages and parenting and saving for retirement. We turn into efficiency experts, seeking ways to preserve success and prevent failures as both begin accumulating in larger numbers. We become concerned with what we can keep as much as what we can create. Eventually, the vaguely disturbing illusion that we’ll live forever vanishes. Heading into retirement, we try to protect what we’ve worked so hard to gain, shifting from promotion motivation to prevention motivation.
It’s a good name, goaded by the ultimate irony of life: death. Now we see ourselves in terms of preservation because time is short. Present happiness becomes more important than future reward. With creaking joints, friends dying, and loved ones moving away, a night with Lucille Ball might just be the ticket.
In a nutshell, that’s the relationship these shifting feelings have with risk taking. We become eager to shun potential hazards and embrace smaller rewards simply because we may not have many rewards left to enjoy. After the twelve thousandth time on a roller coaster, you realize that it’s not going to harm you and there’s still plenty of joy to wring from the experience. What, then, is the harm in making it 12,001?
Smell a rat?
As I mentioned, I have not told you the whole story about seniors and happiness, and there’s a reason for my cowardice: it’s not all razzleberry dressing and theme-park rides. Here’s a true example of how sad this not-good-news can be.
A widowed seventy-four-year-old physician from Southern California found the loneliness excruciating; he eventually signed up for a dating website. The good doctor quickly found an anesthetic in the form of a forty-year-old British divorcée. She was broke, with a daughter in college. In a few weeks, they were cyber-buddies, and weeks after that, long-distance lovers, the digital equivalent of a winter/summer relationship. You probably already smell a rat, and we might wish the doctor had, too.
The woman contacted him in a panic one day. Her daughter had been killed in a car wreck. She didn’t have the money to pay for the funeral, nor her daughter’s student loans, and could he wire her $45,000 to cover the costs because she just didn’t know where to turn? He sent her the funds—which, of course, opened up a spigot of other requests. A fortnight later it was $10,000 for a new roof, $75,000 for a new Mercedes (yes, Mercedes), and finally, a first-class ticket from London, so she could meet the love of her life at LAX and thank him in person. Sadly, he granted every financial request. The woman never showed up at the airport, though he had readied a limousine, Cristal champagne, flowers, and a room at the Four Seasons. The doctor never heard from her again.
This stuff happens to the elderly all the time. Figures are hard to come by, but MetLife estimates the elderly get bilked out of nearly $3 billion every year. Men and women are equally vulnerable, and successful Beverly Hills family doctors are not immune. It’s proof that older people should be less concerned about running out of life than running out of money.
There’s an obvious reason the elderly become a target: solo seniors sometimes have obese bank accounts. The less obvious reason has to do with the dark side of focusing on the positive all the time. As you age, you also become more trusting, or better to say, more gullible. We even think we know why.
There’s an area of the brain called the insula, a slightly hidden clot of neurons just above your ears. You can think of it as an “ability to know when you’re being taken for a ride” detector. Like so many brain regions, the insula has other subfunctions, ranging from assessing risks to reacting to betrayals to feeling disgusted. It even helps forecast whether a given action will be safe. As you age, the anterior insula (front area, nearest your eyes) becomes less reactive to potentially untrustworthy, even threatening, situations. Scientists can show the effects of this decline in many ways, including the capacity to detect untrustworthiness in people’s faces. Or in fake British lovers.
This vulnerability is part of a general collapse of an extremely important behavior: the ability to know when you’re making a mistake about something—especially if rewards are involved. It’s part of a general suite of behaviors called reward prediction, which is the ability to forecast when a reward is most likely to happen (or not). Reward prediction abilities decline more than 20 percent with age, which means reward prediction errors increase. (A reward prediction error is where you anticipate that a reward will occur, based on prior experience, but it doesn’t, so you are wrong.) And just to complete the circle, the aging brain gets worse not only at predicting rewards but also at assessing risks.
There’s more bad news. As if a flickering insula wasn’t enough, there is an area in the brain I sometimes call the AC/DC network (the “Highway to Hell” circuit) that changes as we age. The Highway to Hell is a ridiculously powerful series of linked circuits deeply embedded in your brain, close to the insula. The circuits are responsible for many things, including nearly all addictive behaviors. Hence the name. They are also involved in reward prediction errors, mediating what we call “probabilistic learning,” a skill at which you get increasingly bad with old age. Researchers believe these two regions, the insula and the Highway to Hell, are the reasons why older people become more gullible. And why people who love us need to take special precautions if they take care of us. An aging insula and accompanying circuitry are as dangerous as a broke lover.
A darker shade of gray
I still remember the first time I heard these lyrics over the car radio: “Ooh, what a lucky man he was.” I got goose bumps. I was amazed as the song ended with one of the strangest keyboard sound clusters I’d then encountered. I didn’t normally listen to rock in those days—still don’t (I prefer Stravinsky to the Stones), but I wanted to know more about this group. It was a trio, sporting a name more like a law firm than one of the great prog-rock groups of the ’70s: Emerson, Lake & Palmer. When I discovered they also did electronic covers of classical pieces, it was love at first toccata. I was especially enamored of the virtuosity of the group’s legendary keyboardist, Keith Emerson. Thus it was with sadness that I read about Emerson’s suicide, in 2016, at age seventy-one. Though he kept the dogs of depression at bay for years, his resistance ended when he developed career-threatening nerve damage to his fingers. Gun in hand, he became not such a lucky man after all.
Depression and suicide go hand in hand, as Emerson’s life illustrates. Depression and old age go hand in hand, too, which his life also illustrates, and this represents the deepest shade in the dark side of our chapter on happiness. It also seems to contradict virtually everything I’ve been discussing so far. I obviously have some explaining to do. And with help from two quotes in the research literature, I intend to do just that.
First, we need a quick definition of depression. That’s important because people often confuse depression with normal sadness. In fact, seniors in the grips of depression often don’t feel particularly sad. Instead, they become increasingly unfocused and demonstrably more irritable and restless, and they experience a steady erosion in things they used to find pleasurable. We also need to take into account the fact that triggers for depression—health failures, deaths of loved ones, unremitting pain—are routine events for the elderly.
Older literature about senior depression, such as our first quote (from the surgeon general of the United States, circa 1999), says things like: “Depression is not a normal part of aging . . . serious depression is not ‘normal’ and should be treated.” True? Though the appeal for treatment is spot-on, later research showed the rest of that quote is true only if you don’t look too closely. If you do look closely, you run right into our second quote (from researcher Ke-Xiang Zhao, at Chongqing Medical University in China), which takes issue with the idea that depression isn’t typical: “Older age appears to be an important risk factor for depression in the general elderly population (aged below 80 years).”
Reconciling these seemingly different perspectives, it turns out, depends on how often you had to visit the hospital. For moderately healthy seniors, depression isn’t typical. For seniors whose health is impaired, it’s a different story. (And it’s a good thing that researchers made the distinction, because if they lumped everyone together, they could be fooled into thinking they’re looking at “natural erosion” rather than “unnatural disease progression.”)
Here’s what we know now: the more health challenges seniors encounter, the greater their depression risk becomes. The type of disability is the major contributor, with chronic disease taking pole position. One of the biggest contributors to depression is hearing loss. Another biggie is vision loss. Others are the various cancers, chronic lung diseases, strokes, and cardiac diseases. Unknown are the effects of diabetes and hypertension.
If seniors live in community settings, depression chimes in at a modest 8 percent to 15 percent. Hospitalize them because of some physical ailment, or simply put seniors into assisted living, and the prevalence soars to 40 percent. That’s a big deal. Depression is now projected to be the leading cause of disease burden in the elderly by 2020. The bottom line is that happiness increases in older populations as long as seniors remain healthy. But since health naturally ebbs in aging populations, the rate of depression rises.
Is there something we can do? Though the answer is yes, we must revisit some brain biology to understand our options, examining one of the happiest biochemicals on earth. Would that Keith Emerson could have become better acquainted with it.
Dopamine’s decline
“That’s the problem,” my dad chuckled one cold winter morning in 1966, holding up a small, jewel-like bauble for me to inspect. It looked like the threaded end of a decapitated Christmas light. “If we replace the old guy with this one, the kitchen’s gonna work good as new.”
Earlier that morning, my ten-year-old self had marched into his bedroom, horribly alarmed that I had broken the entire kitchen. I had plugged in a portable space heater near the fridge, then heard a loud pop. The kitchen immediately stopped working. No lights, no refrigerator, no stove, no electric can opener.
“All you did was blow a fuse, Son,” my dad said, fingering his glittering electrical ornament, a spare (now vintage) fifteen-amp household fuse. I was amazed. How could such extensive culinary destruction—from refrigerators to ovens—result from something so small, so singular? I got my first lesson in how electrical circuits worked in houses. Dad unscrewed the old fuse and put in the new one; sure enough, the kitchen roared back to life.
This electrical nostalgia illustrates something useful about brain wiring and its activating circuitry. I’ve mentioned many behavioral changes in this chapter: decision making, award seeking, risk taking, selective memory, depression. These behaviors might seem as functionally disconnected as a can opener from a freezer. But they aren’t disconnected at all. Scientists believe the biological basis for most of these changes comes from the failure—just like in that kitchen—of a single circuit.
This circuit isn’t made of wires responding to electricity, of course; it’s made of neurons responding to a neurotransmitter. The neurotransmitter is a famous molecule I’ll bet you’ve heard of before: dopamine. The circuits over which dopamine exerts its powers are called dopaminergic pathways. The brain has about eight of these pleasure-coaxing pathways.
One of the first impressions you’d get if you ever bumped into a molecule of dopamine is how ridiculously small it is. It’s synthesized by redecorating an amino acid called tyrosine. Remember amino acids from high school biology? They’re the natural building blocks of proteins. To make a protein, long strings of amino acids—sometimes hundreds—are strung together like cars in a train. Dopamine is the size of just one of those train cars.
You may also be familiar with tyrosine because of your diet. Most of you eat it every day. Egg whites have a lot of tyrosine. So do soybeans. And seaweed. Don’t be fooled by its size or pedestrian origins, however. Dopamine packs a serious wallop. Make too little of it and you might get Parkinson’s disease. Make too much of it and you might get schizophrenia. When you synthesize just the right amounts, dopamine mediates your ability to reward yourself with pleasure, your ability to hold a pen without shaking, and your ability to make decisions. Every one of the behaviors mentioned in this chapter at some level involves dopamine. Impressive skill set for a clump of seaweed.
How does this polymath of a molecule do it? Dopamine mediates its activities by binding to a family of receptors built for it. These receptors are found only on certain neurons in the brain. Cells lucky enough to sport the receptors are activated to perform certain functions when dopamine binds to them. Think of it as the ignition system inside your standard Honda. Insert the key into the lock, and the car springs to life. Insert the dopamine into its neuron-bound receptor, and the neuron springs to life. Put many of those neurons in a row, and you have an activatable circuit. Put eight or so of those circuits together, stuff them deep into the center of the brain, and you have the dopaminergic system.
Given the brain’s Shanghai-esque overpopulation of cells, the dopaminergic system involves remarkably few neurons. Only certain regions contain dopamine receptors, which means only certain regions of the brain are sensitive to dopamine. One prominent area is the “Highway to Hell” circuit I mentioned. This highway consists of two small dopamine-sensitive brain regions (the ventral tegmental area and the nucleus accumbens) connected by dopamine-sensitive circuits. Over-driving this system—and thus dysregulating it—is responsible for most of the chemical addictions that regularly devour human beings.
Dopamine, it turns out, is a really big deal. And we are about to find out just how big a deal it is for seniors. One of the hallmarks of aging is that the dopamine system, after a while, begins to fade away.
The mouse that didn’t roar
Some experiments are tough to digest, like an overcooked steak, and this is one of them. You can genetically manipulate mice in such a fashion that they can’t make dopamine by themselves. When you do that, you give them a death sentence. The reason is startling. The animals starve to death. Even if you put their favorite foods in front of them, the rodent equivalent of chocolate cake, they will sit there beside the food, blinking at it, doing nothing to intervene as death slowly envelops them. Same for baby mice. Without intervention, dopamine-deficient pups won’t suckle frequently enough to sustain their little lives. They still have the behaviors necessary to look for the food and eat. They just aren’t willing to eat. Intervene by administering dopamine artificially, and everybody starts to eat normally. The point? Life without dopamine can be very difficult to sustain. Life with dopamine is, to understate the obvious, the preferred option.
The reason I bring up this experiment concerns one of the most solid biological findings that exists in the gerosciences: as humans age, the dopaminergic system begins functionally to decline. In humans, this decline has consequences much more complicated than simply changing our pleasure in eating. Since the human brain has a cortex the size of a baby blanket, and lab rodents have one the size of a postage stamp, such differences make sense.
The erosion in humans has three parts. First, the manufacture of dopamine slows down in specific regions of the brain. It’s an uneven assault. Midbrain loss is smaller, whereas loss in the forehead-dwelling dorsolateral prefrontal cortex is almost threefold greater. The effects are especially noticeable after age sixty-five. Second, dopamine receptors begin to disappear. One important receptor, dubbed D2, declines 6–7 percent with each decade of life, beginning around age twenty! Third, dopaminergic neural circuits begin flickering off, mostly because of cell death. One commonly hard-hit region is the substantia nigra, a piece of neural real estate deeply involved in motor function. Parkinson’s disease can result, which explains why one of the greatest risk factors for getting it is simply growing old.
These three categories of losses may explain virtually every behavior discussed in this chapter. Certain types of depression occur because of a loss of dopaminergic activity, for example. So common is the experience, it’s been given its own name—DDD, for dopamine deficient depression.
We also know that dopamine is involved in mediating command decisions—particularly reward prediction—which, as you recall, is a skill that diminishes with age. Dopamine mediates the willingness to take risks, which also declines. Dopamine is even associated with our psychological motivations. Given that age transports us from aggressive promotion motivation to cautious prevention motivation, we may be observing the alteration of a singular suite of risk-associated behaviors.
Even the positivity effect (and its darker twin, gullibility) may be explained by dopamine loss. We know that attentional networks, which allow us to preferentially select one set of stimuli over another, are profoundly influenced by dopaminergic activity. Indeed, most of the major players in those networks use dopamine to direct the focus of our brains. That includes the insula (coincidentally also involved in gullibility), which in youth is studded with dopamine receptors like cloves on a ham. A dysfunctional insula, by the way, is also associated with depression.
What about seniors who report being happier as they get older? Does dopamine dysregulation play a role here, too? The real answer is we don’t know. As we’ve seen in this chapter, the happiness data are nuanced, especially when other factors are considered (like diseases and depressions). Since these studies were done primarily with healthy seniors, “healthy” may also include intact dopamine pathways. In which case, scientists were studying only a subset of the population.
Or not. As we’ll see in the memory chapter, the brain is surprisingly good at conjuring up compensatory behaviors for cognitive functions it knows are eroding. The happiness data may represent the determined effort of a brain, faced with inexorable dopamine decline, refusing to go down without a fight. Or a smile. Many seniors I know still light up in the presence of chocolate cake and start looking for a fork. I’m one of them.
Awakenings
While scientists in various corners of the research world are actively investigating these processes, others have skipped ahead of the biology and gone right to the clinic. They are interested in determining what, if anything, could be done practically for patients now. If dopamine loss is so deeply associated with behavioral decline, they asked, could that decline be arrested by artificially resupplying the molecule? Research suggests there might be something to this idea.
One of the most surprising examples of this practical approach originates from a 1973 book called Awakenings, a true story written by famed neurologist Oliver Sacks, made into a movie years later.
The book wasn’t about patients suffering the consequences of aging. It was about patients suffering the consequences of infection (encephalitis). The disease left most of the patients catatonic, wheelchair bound, seemingly alive in name only. When one of these closed-for-business people (played in the movie by Robert De Niro) was administered a synthetic form of dopamine, it was like giving him a syringe filled with the Fountain of Youth. He suddenly awoke from his catatonia. He started smiling, walking, talking, wanting to fall in love—Sleeping Beauty responding to a kiss from Prince Dopamine.
This synthetic dopamine, biochemical royalty in the world of neuroscience, is called L-DOPA. (You can’t use real dopamine because it strangely refuses to jump into the brain.) L-DOPA has triggered at least two Nobel prizes, mainly for treating Parkinson’s disease. Studies have also shown positive effects on cognitive processes not associated with disease states but simply with typical aging.
Consider reward prediction, which withers with age. You can alter its fall from grace by taking L-DOPA, literally improving a complex cognitive process on the back of a simple synthetic. The effect isn’t small. The treated seniors’ laboratory performance becomes indistinguishable from that of younger, untreated controls.
L-DOPA increases your preference for looking on the Doris Day side of life, too. It elevates something called optimism bias, prejudices about which seniors know a great deal. But this experiment was not done with seniors. It was done with a younger generation, known more for loving snark than Singin’ in the Rain. It caused the author of the experiment to declare: “This study does show that optimism may be influenced by dopamine levels even in healthy people. And that’s a pretty glass-half-full kind of study.”
That’s especially good news for seniors. Optimism is not just emotional insulation against the freezing wastes of mortality. We now know that elders who have positive, even optimistic, attitudes toward their own aging live longer than those who don’t.
What do I mean by optimistic aging? A twenty-five-year-old who forgets somebody’s name seldom considers it a harbinger of Alzheimer’s disease. But if you’re older and your memory transmission slips a gear, you might very well worry about Alzheimer’s. You may become stressed, even depressed. As other roadside attractions of age come into view—from hearing loss to aching joints—your attitude may turn increasingly pessimistic. The data say: don’t go there. Seniors who take it in stride, convincing themselves the glass is still half-full, live a healthy 7.5 years longer than seniors who don’t. Optimism exerts a measurable effect on their brain. The volume of their hippocampus doesn’t shrink nearly as much as the glass-half-empty crowd’s does. That’s an important finding. The hippocampus, a sea-horse structure located just behind your ears, is involved in a wide variety of cognitive functions, including memory. My guess is that dopamine levels are affected, too. These seniors avoid the trap of what would otherwise turn out to be a self-fulfilling prophecy.
And you don’t need a drug to practice optimism.
That leads to an important question: Should you rely on drugs in an effort to set this attitudinal shift in concrete? The movie Awakenings may be instructive here, too, as it’s based on something that really happened. The effects of L-DOPA turned out to be temporary. Robert De Niro’s character eventually returned to his catatonic state, as did all his colleagues. The movie ends with one of the saddest dances in film. Though it has done great good, L-DOPA comes, as all drugs do, with some important side effects, including hallucinations and psychoses—and in the case of encephalitis, term limits.
Are there ways to maintain optimism (and possibly elevated dopamine) that do not require drugs? Something that yields a more permanent, more side-effect-free future? The answer, happily, is yes. It all revolves around the hidden part of what scientists mean when they say, “Don’t go there.”
Oprah Winfrey had an unpleasant childhood, to put it mildly. She still remembered those difficult roots when she became famous, lending her rags-to-riches story authenticity. She once said: “Though I am grateful for the blessings of wealth, it hasn’t changed who I am. My feet are still on the ground. I’m just wearing better shoes.” Consistent with this attitude, Winfrey started jotting down all those blessings, a journaling habit she sustained for a decade. There are scientific reasons why it was good that she did. Winfrey probably knew this: her emphasis on gratitude ran smack into some solid cognitive neuroscience, enrobed in a body of thought called positive psychology. The research I’m describing comes from its father, Martin Seligman, who used to study trauma and depression.
