There is yet another omission. Taylor sides with the standard neuroanatomical belief that
neurons, the primary cell of the nervous system, do not multiply (for the most part) after we are born. That means that the majority of the neurons in your brain today are as old as you are.
While it is true that neurons don’t multiply, she leaves out recent view-changing discoveries that the brains of adult mammals—including humans—are not doomed to steady attrition from ongoing death of neurons and other key cells, whether from natural causes, disease, or injury. New brain cells can be formed and old ones replaced, thanks to the presence in parts of the brain of stem cells, astonishingly versatile progenitor cells that can differentiate into nerves or their neighboring supporting cells. There’s now no doubt that neurons deriving from stem cells, once given a start, mature into normal nerve cells that integrate and develop connections (synapses) with other neurons.3
This discovery represents a critical scientific breakthrough that has opened a new and promising avenue for the treatment of currently incurable nervous system disorders such as Alzheimer’s and Parkinson’s diseases. Such treatment might even promote the emergence of new neurons in areas of the brain impaired by a stroke such as Taylor had, either by stimulating new brain cell formation from resident stem cells or by transplanting harvested ones directly into damaged regions of the brain.
By far the most interesting and probably controversial sections of Taylor’s book concern the gigantic and amazing functional differences between the two cerebral hemispheres: the bulky upper parts of the brain, which are easily recognized by their wrinkly corrugated external surfaces. Although the two hemispheres look identical and they are wired together by a vast network of nerve fibers, they regulate competing neurological functions and they “process information in uniquely different ways.” Taylor defines dominance within the brain as “which hemisphere houses the ability to create and understand verbal language.” The 85 percent of Americans who are right-handed are virtually all left hemisphere dominant. Left-handed people (like both of the authors of this review) have always believed that they were the opposite—therefore special—but it turns out that “over 60 percent of left handed people are also classified as left hemisphere dominant.” Which hemisphere controls what is an important part of Taylor’s argument.
A pop-psych view that has been around for a long time has been more or less validated by research: located within their respective hemispheres are our left minds and right minds. Of the two, according to Taylor, the usually dominant left mind is thought to be the more hard-nosed, verbally oriented, preoccupied with down-to-earth task-dependent details, and unsentimental. By contrast, our right minds don’t think in words but in pictures (at least that is what hers did), are concerned with the abstract glory of the moment (not how it relates to the past, present, and future), are rich with pleasant sensations, such as joy and inner tranquillity, and are free of inhibitions and judgment.
Ordinarily, our two minds work in concert depending on the sensory input from our immediate environment and what we are engaged in at the time, as well as on our past experiences and on our present expectations with, usually, the more practical left mind predominating. But Taylor’s hemorrhage disabled her mundane left mind, thus liberating her right mind, which rejoiced in its newly found freedom. Taylor made a slow (seven years) but nearly complete recovery, and as her left brain began to regain its power, she became convinced that she could select which of its old programs she wanted to retain—the pleasant helpful ones—and which she wanted to reject—the “stubborn, arrogant, sarcastic and/or jealous” egocentric functions. She ended up with “the power to consciously choose which emotional and physiological loops” she wanted “to hook into,” and suggests—not entirely persuasively—that we can all do the same:
One of the greatest blessings I received as a result of this hemorrhage is that I had the chance to rejuvenate and strengthen my neurocircuits of innocence and inner joy. Thanks to this stroke, I have become free to explore the world again with childlike curiosity. In the absence of obvious and immediate danger, I feel safe in the world and walk the earth as though it is my backyard. In the consciousness of my right mind, we are laced together as the universal tapestry of human potential, and life is good and we are all beautiful—just the way we are.
Some say that months or even years of meditation may lead to the same level of inner consciousness that Taylor enjoys, but we should not hope for strokes to get us there. One wonders whether, without the useful computer-derived metaphors of “program” and “circuit,” she would describe her improved character with old-fashioned philosophical terms like “wisdom” or “maturity.” Strokes are the third most common cause of death in the United States, and high on the list of chronic disablers (right up there with arthritis and depression): Taylor’s must be the only one that was ever welcomed with enthusiasm.
Both Manguso’s and Taylor’s books send strong positive messages that by combining deep personal resolve and courage with excellent medical care, people can bounce back from life- destroying illnesses, and that a will to survive is innate and, ordinarily, admired. David Shields, however, wonders whether or not that makes sense; he is in a long tradition of pessimism when he reminds us that after all The Thing About Life Is That One Day You’ll Be Dead. In the course of expressing this attitude, Shields has occasion to tell us a great deal about his father, Milton, a vigorous senior citizen of dubious likability, who has made it into his mid-nineties by regular jogging and tennis, maintaining his youthful weight, and as much lovemaking as he could find partners for.
Now, at ninety-seven, Milton has lost much of his energy and has become terminally bored with life, but still wants desperately to live to be one hundred. The text alternates between his determination to stay in shape, watch his diet and weight, and live forever, and David Shields’s rather sadistically wielded statistics that underscore why this is not going to happen. The reader earnestly hopes Mr. Shields will make it, if only to refute his son’s sour realism, with its unpleasant implications for us all.
We don’t learn why there are so few centenarians—only one in ten thousand people live that long—until well into the book, when Shields makes the key point that nature’s biological imperatives are only focused on perpetuating the species and are afterward indifferent to our fate. In America, for instance, more than 90 percent of people now live to be at least fifty, the crucial age that marks the onset of both menopause (the end of reproductive capacity) in women and the waning powers of procreation in men; but, unlike some insects and salmon, humans don’t die when they finish reproducing: they are likely to live another twenty-five or thirty years. (In 2005, life expectancy for American women was 80.4 years and 75.2 years for men.)
On the one hand, all this post- reproduction survival time can be viewed as evolutionary largesse, but on the other hand, it is also a long preparation for death, characterized by relentless physical and mental attrition. Beginning in the twenties and thirties, but accelerating in the forties, fifties, and sixties, is a steady age-related waning of physical performance as the lungs and heart reduce their capacities to deliver oxygen into the bloodstream and pump it around the body; blood vessels harden and become less elastic; muscles shrink and weaken; reflexes slow and coordination worsens; bone density decreases and fragility increases; and the usually vigilant immune system no longer protects against the onset of infection and the transformation of healthy cells into malignant ones. These are regular phenomena, to be sure, but with huge individual variation—and the possibility of, to some extent, remediable measures, such as physical exercise.
Shields seems to delight in documenting this attrition with one dire statistic after another, but he never reminds readers that these kinds of epidemiologically based data are derived from large numbers of subjects, often carefully selected and unrepresentative, for instance nurses or military recruits, and can’t say what is in store for a particular person, for instance Milton Shields. David Shields clearly buys into the theory that aging is under genetic control. After all, genes control our physical appearance, our internal cellular machinery—such as how we respond to stress, whether we react to various medications, whether we tolerate milk and cheese—as well as our susceptibility to and the age of onset of many of the numerous diseases that complicate aging and can bring life to an end.
In addition, several groups of investigators have found ways of greatly extending the life expectancy of various species of laboratory animals by genetic manipulation. Of these experimental tricks, the most robust and reliable is calorie restriction, which extends longevity in rats, fruit flies, worms, fish, mice, and hamsters, and is now being tested (and seems to be succeeding) in monkeys; the mechanisms at play are unknown, but probably involve activation of survival genes that shift the body’s metabolism into a slower, live-longer mode. The idea is interesting, and Shields is attracted to it, but we can only wonder how many humans are going to stick to the draconian restriction in their daily caloric intake, the technique customarily used to extend life expectancy in experimental animals; it would mean, basically, that people would have to practically starve themselves for most of their lives.
Genes unquestionably affect how well and how long we live, but many scientists believe that aging happens spontaneously, without a genetic program. According to the “no genetic blueprint” theory, aging represents the accumulation of biochemical and physical wear and tear, from both internal and external assaults, of vital cellular metabolic machinery. These theories are not mutually exclusive and it seems likely that both wear and tear and genetic influences determine how long we live. But for centuries, the most important determinant of longevity has been wealth, and this remains true today even in industrialized countries like France, where good health care systems are available to everyone. Compared with poor people, the rich have better nutrition and less obesity, they exercise more, smoke fewer cigarettes, and seek medical help sooner. Shields does not mention something that is rarely discussed about American health: the fact that despite our wealth, we are only thirtieth in average life expectancy, tied with Costa Rica, Kuwait, and Slovenia, and far below Japan, Australia, Canada, and all the Western European countries; the same is true for other measures of public health efficacy.
Shields’s father has practiced what many now preach concerning how to extend life. He’s a strong advocate of “nutritional discipline”; he retained his trim youthful weight throughout adulthood; and, he told his son, “the secret of a long, healthy life is to exercise every day even if it’s only for thirty minutes, and don’t let anything deter you from it”—recommendations identical to those that have been both endorsed and widely promoted by numerous public health authorities and professional medical and sports associations. We never really learn why Shields has obliquely chosen to denigrate these eminently sensible guidelines, but we can guess it has something to do with his feelings about his father. At the end of his book, he recounts a nightmare in which he’s in a foot race with the elder Shields: “He wins. He wins again. He always wins—except in the sense that in the end he’ll lose, as we all do.”
Do we really need reminding of this?
See Morten C. Moe, Mercy Varghese, Alexandre I. Danilov, et al., "Multipotent Progenitor Cells from the Adult Human Brain: Neurophysiological Differentiation to Mature Neurons," Brain, Vol. 128 (2005), pp. 2189–2199.↩
See Morten C. Moe, Mercy Varghese, Alexandre I. Danilov, et al., “Multipotent Progenitor Cells from the Adult Human Brain: Neurophysiological Differentiation to Mature Neurons,” Brain, Vol. 128 (2005), pp. 2189–2199.↩