Excerpted from The Wisdom Paradox: How Your Mind Can Grow Stronger As Your Brain Grows Older by Elkhonon Goldberg. ©2005 by Elkhonon Goldberg. Published by Gotham Books, a division of Penguin Group (USA) Inc. Reprinted with permission.
Is the aging of our brains all gloom and no triumphs? I don’t think so. In fact, I will use all the mental vigor left in my own aging brain to promote the thesis that the aging of the mind has its own triumphs that only age can bring. That is the central message of this book.
It is time to stop thinking about the aging of our minds and our brains solely in terms of mental losses, and losses alone. The aging of the mind is equally about gains. As we age, we may lose the power of our memory and sustained concentration. But as we grow older, we may gain wisdom, or at least expertise and competence, which is nothing to sneer at either. Both the losses and the gains of aging minds are gradual rather than precipitous. Both are rooted in what happens in our brains. There have been enough books written about the losses of aging minds. This book is devoted to the gains, and the balance between the losses and the gains.
Our culture demands a happy ending to every story. As a product of a harsher environment in my youth, I ﬁnd this amusing to this day, despite the fact that I have lived this side of the Atlantic for three decades. I recall a television interview I watched after a particularly cataclysmic event of recent years. After a talking-head expert painted a dramatically stark and unfortunately accurate picture of the issue at hand, the interviewer, a famous TV personality, said with a tinge of impatience and even entitlement: “But what can you say to reassure the American public?” At which point I said to myself, What an interesting cultural idiom! Give me a happy ending or else!
Reassurance is not always a good thing. There are circumstances when grabbing the public by the scruff of its collective neck, so to speak, and shaking it up with alarm will do more good in the long run. But on the issue of aging the public has already received its therapeutic shake-up dose. We hear constantly about the scourges of dementia and Alzheimer’s disease, and about the symptoms of neuroerosion, the encroachment of forgetfulness and increasing mental fatigue. Unfortunately, these scourges are real. But it is time to look for good news, providing that the good news is also real and not a phony “reassurance” ploy.
Wisdom is the good news. Wisdom has been associated with advanced age in the popular lore of all societies and through history. Wisdom is the precious gift of aging. But can wisdom withstand the assault of neuroerosion, and for how long?
This raises a question about the nature of wisdom. In our culture we use the word frequently and reverently. But has wisdom ever been sufﬁciently deﬁned? Its neural basis understood? Can the phenomenon of wisdom be understood in principle in biological and neurological terms, or is it too elusive and multifaceted to be tackled with any degree of scientiﬁc precision?
Without claiming any particular wisdom of my own, I believe I can contribute to this understanding by enlarging on my earlier introspections, which help elucidate the nature of wisdom, or at least one important aspect thereof. The train of thought and the argument developed in this book will ﬂow from this introspection and this insight.
With age, the number of real-life cognitive tasks requiring a painfully effortful, deliberate creation of new mental constructs seems to be diminishing. Instead, problem-solving (in the broadest sense) takes increasingly the form of pattern recognition. This means that with age we accumulate an increasing number of cognitive templates. Consequently, a growing number of future cognitive challenges is increasingly likely to be relatively readily covered by a preexisting template, or will require only a slight modiﬁcation of a previously formed mental template. Increasingly, decision-making takes the form of pattern recognition rather than of problem-solving. As the work by Herbert Simon and others has shown, pattern recognition is the most powerful mechanism of successful cognition.
Evolution has resulted in a multilayered brain design, consisting of old subcortical structures and a relatively young cortex with a particularly young subdivision appropriately called the neocortex. The cortex of the brain is in turn divided into two hemispheres: right and left. The passage from problem-solving to pattern recognition changes the way these different parts of the brain contribute to the process. Firstly, cognition becomes more exclusively neocortical in nature and increasingly independent of subcortical machinery and of the machinery contained in the old cortex. Secondly, the balance of our use of the two hemispheres of the brain shifts. As I will show, in neural terms this probably means a decreasing reliance on the right hemisphere of the brain and an increasing reliance on the left cerebral hemisphere.
In neuroscientiﬁc literature, the cognitive templates that enable us to engage in pattern recognition are often called attractors. An attractor is a concise constellation of neurons (nerve cells critical for processing information in the brain) with strong connections among them. A unique property of an attractor is that a very broad range of inputs will activate the same neural constellation, the attractor, automatically and easily. In a nutshell, this is the mechanism of pattern recognition.
I believe that those of us who have been able to form a large number of such cognitive templates, each capturing the essence of a large number of pertinent experiences, have acquired “wisdom,” or at least a certain crucial ingredient thereof. (As I write this, I hear the indignant howling of critics from various corners of science, humanities, and social activism, accusing me of scandalously gross oversimpliﬁcation, so I am hedging my bets.)
By the very nature of the neural processes involved, “wisdom” (at least in my admittedly narrow deﬁnition of it) pays dividends in old age by allowing relatively effortless decision-making requiring only modest neural resources. That is, modest as long as the templates have been preserved as neural entities. Up to a point, wisdom and its kin qualities, competence and expertise, may be impermeable to neuroerosion. These will be the main themes of the book.
NEW EVIDENCE FOR NEW NEURONS
“Use it or lose it” is a well-worn adage traditionally ﬁnding its meaning in the world of athletics. But lately it has found a new meaning in brain science. In the course of the last decade, spectacular discoveries have been made that changed our basic assumptions about what happens to the brain in the course of a lifetime and upended some of the most sacrosanct beliefs in neuroscience. As recently as two decades ago, we used to think that a human being was born with a ﬁxed collection of nerve cells in the brain (neurons), which gradually died out as we aged without any possibility of regeneration. As a graduate student at the University of Moscow in Russia many years ago, I referred to this assumption (which was ideologically agnostic and prevalent on both sides of the Iron Curtain), jokingly and skeptically, as the NNN principle—“No New Neurons!”
In the course of the last decade, spectacular discoveries have been made that changed our basic assumptions about what happens to the brain in the course of a lifetime and upended some of the most sacrosanct beliefs in neuroscience.
Neuroscientists recognized that the NNN principle set the brain apart from the rest of human body, since most other organs have the capacity for regeneration. Neuroscientists also recognized that the NNN principle as not ubiquitous, since it has been known for years that the brains of several bird and rat species do have the capacity for regeneration.
For years a handful of iconoclastic scientists like Fernando Nottebohm and Joseph Altman were trying to draw the attention of the neurobiological community to these animal research ﬁndings and to their implications for human therapies. But their efforts were dismissed as irrelevant to the human brain. It was thought that humans were different, that the inability to regenerate new neurons was the price that we had to pay for the privilege of hanging on to the old neurons, the neurons that encoded our previously acquired knowledge, our memories, ourselves.
On the surface, this sounded like a plausible exercise in “neuroteleology,” since, as we have abundantly established, humans depend on previously accumulated or learned knowledge far more than any other species. But on closer scrutiny the argument does not hold up, since we lose our old neurons anyway in the course of life, whether we like it or not. Neurologists and neuropsychologists know very well that even in perfectly healthy people CT or MRI scans of the brain look differently at different ages, suggesting some degree of neuronal loss. As we already know, in normal aging the neuronal loss seems to occur both in the neocortex, where the pattern-recognition generic memories are contained, and in certain subcortical structures and around the ventricles, the cerebrospinal ﬂuid-containing cavities deep inside the brain. Since the neocortex is clearly not entirely spared, the only explanation of how we endure neocortical neuronal loss without the loss of essential, previously accumulated knowledge is by assuming that our memories, particularly the generic memories, are stored in a highly redundant fashion. Such redundancy is reﬂected in, among other things, the “pattern expansion” discussed in the previous chapters.
The NNN axiom, regarded as ironclad for decades, ﬁnally became indefensible with the work of Elizabeth Gould and others, who have demonstrated the existence of ongoing neuronal proliferation in several monkey species. Monkeys are too close to humans to dismiss such ﬁndings as irrelevant, and the monkey ﬁndings are particularly exciting because they show the proliferation of new neurons in the heteromodal association cortex of the frontal, temporal, and parietal lobes. It was also shown that new neurons continue to grow throughout the life span in the hippocampi. All these parts of the brain are especially important in complex cognition, and they are particularly vulnerable both in normal aging and in various forms of dementia, including Alzheimer’s disease. Potentially, the ﬁnding of lifelong neuronal proliferation in the neocortex and in other parts of the brain (including the hippocampi, so important in the formation of new memories) opens the door for a wide range of therapies in humans.
Today, we know that the old premise of “No New Neurons!” is simply not true. New neurons constantly develop out of stem cells throughout a lifetime, even as we age. So our brain has the ability to restore and rejuvenate itself. Contrary to long-held beliefs, neurons do not stop developing in infancy. Far from it; they continue to grow throughout the whole life span, well into adulthood and even into advanced age.
Furthermore—and this is particularly important—there has been growing evidence that the rate of development of new neurons could be inﬂuenced by cognitive activities in a way not dissimilar from the manner in which muscle growth can be inﬂuenced by physical exercise. This was demonstrated with particular clarity in experiments conducted at the Salk Institute, one of the premier centers of biomedical research in the world. A much greater rate of new neuronal development (up to 15 percent more) was noted in mice immersed in an environment ﬁlled with toys, wheels, tunnels, and other “mouse-brain teasers,” than in idle mice left to their own devices. The mice from the enriched environment have also shown signiﬁcant advantages on various tests of rodent intelligence. The neuronal proliferation triggered by cognitive exercise was especially pronounced in the hippocampus. The ﬁnding is of paramount importance because, as we have seen, the hippocampus is particularly important in memory and is among the brain structures most affected at the early stages of Alzheimer’s disease. Not surprisingly, the levels of chemicals stimulating the growth of new neurons in the brain also increase as the result of exercise. This was demonstrated for the Brain-Derived Neurotrophic Factor, or BDNF for short.
While much of the early evidence was obtained in animals, direct human evidence is also beginning to appear, causing great excitement in the scientiﬁc and biomedical communities.
Some of the recent ﬁndings are truly dramatic. It has been shown, for instance, that new neurons continue to appear in the adult human hippocampi. This ﬁnding, ﬁrst reported by the Swedish scientist Peter Eriksson, has become frequently quoted in neuroscientiﬁc literature. What’s more, new neurons continue to proliferate not only in healthy brains but also in the brains of patients suffering from Alzheimer’s disease. Findings like these certainly breathe new life into the “use it or lose it” adage. One is tempted to rephrase it, “Use it and get more of it.”
The notion that mental activities can actually change the brain is gaining an increasing number of supporters in the scientiﬁc and biomedical communities. Much of the recent work on the subject has been reviewed in an excellent book by Jeffrey Schwartz and Sharon Begley, The Mind and the Brain. But what exactly happens in the human brain as a result of vigorous mental activity? If you asked me this question a decade ago, I would have said that the connections between the neurons become more numerous and stronger. This would imply a more vigorous growth of dendrites and synapses, and the development of extra receptor sites, to which the neurotransmitter molecules bind. I would have also said that the small vessels carrying blood (and through it oxygen) to different parts of the brain proliferate.
I still say all of these things. But the past decade brought new, even more stunning discoveries about the brain’s plasticity and how it continues to be molded by environment throughout the lifetime. We know this from animal research, which brought about a true revolution in our thinking about the life of the brain. As we have already learned, cognitive exertion increases the rate with which new neurons appear in a wide range of brain structures, which may include the prefrontal cortex, a brain region particularly important for complex decision-making, and the hippocampi, the sea horse-like structures particularly important for memory.
Since all mammalian brains operate on the same fundamental neurobiological principles, we could reasonably assume that the human brain is also capable of producing new neurons throughout the life span. But is there direct evidence of this happening, and can the rate of new neuron production be increased by cognitive exercise in humans as well? This proposition would have sounded so outlandish even a decade ago, and certainly two decades ago, that I probably would have felt my own intelligence insulted by a mere consideration of this possibility. And I would have been wrong!
The ﬁrst evidence that brain structures may actually grow, actually increase in size as a result of environmental factors even on the macroscopic scale, came from none other than...cab drivers. The ﬁnding is especially striking because of its simplicity and direct explanatory relevance. Hippocampi were found to be especially large, larger than in most people, in London cab drivers, whose job requires the memorization of numerous complex routes and locations. Since the hippocampi are so important in memory, and good cab drivers in a huge city like London must memorize a particularly large number of spatial routes and locations, they strain their hippocampi, so to speak, more than most people, just like a weight-lifter strains his muscles more than most people. Furthermore, the longer the cab drivers were on the job, the larger were their hippocampi: The size of the hippocampi was directly proportionate to the number of years on the job. This suggests a direct relationship between the amount of a certain type of cognitive activity and the size of a neural structure involved in this activity.
The cab-driver ﬁndings are remarkable in several respects. First, an important neural structure can continue to grow well into adulthood. What’s more—and this is particularly important—the growth of a neural structure appears to be stimulated by its use. More years on the job generally implies older age, which in turn would suggest hippocampal atrophy. Yet here we have older people with larger hippocampi due to increased mental activity of a particular kind. The effects of vigorous cognitive stimulation seem to offset and override the detrimental effects of aging—perhaps to a substantial degree.
While cognitive exercise stimulates the proliferation of new hippocampal neurons, other factors may retard it. As it turns out, neuronal proliferation in the adult hippocampi is a process both delicate and resilient. It can be upset by, among other things, brain inﬂammation, a condition found in diseases as diverse as Alzheimer’s disease, Lewy body dementia, and AIDS dementia complex. (This is probably due to the disruptive effect of inﬂammation on the brain stem cells, the “prefab” cells that subsequently differentiate into a variety of speciﬁc neurons.) But adult neurogenesis in the hippocampi is restored when the inﬂammation is reduced.
Having established that cognitive exercise spurs the growth of new neurons, we are ready to ask our next question: How speciﬁc are these effects? The brain is a diverse, heterogeneous organ. Different parts of the brain are in charge of different mental functions, and different mental activities call upon different parts of the brain. If mental exercise, the use of one’s brain, stimulates the growth of new neurons, then it is quite plausible that different forms of mental activity will stimulate such growth in different parts of the brain.
For instance, is hippocampal enlargement speciﬁc to those activities that must rely on spatial memory, or is it the case that certain brain structures are sensitive to the effects of any mental stimulation and other brain structures are not? What would be the effects on the brain of other types of mental activities, which rely on vastly different cognitive functions? To expand on the thought, if the hippocampi is enlarged in cab drivers, can we reasonably expect that the left temporal lobe (the language lobe) would be enlarged in a writer, the parietal lobes (the spatial lobes) in an architect, and the frontal lobes (the executive lobes) in a successful entrepreneur? Or is it the case that certain structures, possibly the hippocampi among them, will be enlarged in any profession requiring mental exertion regardless of the speciﬁcs, and certain other structures will not be?
Since different types of cognitive exertion call into action different parts of the brain, it would stand to reason that they will also stimulate extra neuronal proliferation in different parts of the brain. Therefore, the idea that the brain-stimulating effects of cognitive activities are at least somewhat speciﬁc is not totally outlandish. In fact, the more one thinks about it, the more plausible it sounds. But plausible or not, do we have direct evidence to this effect?
THE BILINGUAL BRAIN— AND THE MUSICIAN’S MIND
Spectacular as the London cab driver ﬁnding was, for a while it remained one of a kind. And one study was not enough, precisely because of the ﬁnding’s spectacular nature. The more ambitious a scientiﬁc claim is, the more profound its implications, the higher the bar is set for its acceptance by the scientiﬁc community, and the more rigorous proof that is required. This is one of the most inviolate rules of science, and the cabdriver ﬁndings were received with a degree of caution.
So you can imagine my excitement when in the course of a few hours...[at a recent conference on brain mapping] I stumbled into not one, but two similar ﬁndings, both involving MRI. In the spirit of the meeting, they came from two very different corners of the world.
The ﬁrst study, conducted at the Well-come Department of Imaging Neuroscience of the Institute of Neurology in London, involved MRI measurements of the size of the angular gyrus, a cortical area where the temporal, parietal, and occipital lobes come together. It is part of the heteromodal association cortex, in charge of integrating inputs arriving from multiple sensory channels: visual, auditory, and tactile. The angular gyrus of the left hemisphere plays an exceptionally important role in language, particularly in processing various relational constructs: before/after, above/below, left/right, passive voice, possessive case, and so on. We know all this because of extensive observations of what happens when the left angular gyrus is affected by a brain lesion, such as after a stroke, or by a gunshot wound. Damage to this part of the brain produces severe language impairment, a form of aphasia of a particular kind. The angular gyrus is among most researched parts of the brain, and its functions have been described in numerous scientiﬁc articles and books, including the classic monograph by my mentor Aleksandr Luria, Traumatic Aphasia.
The author of the Wellcome study, a young man pacing a bit nervously in front of his poster, offered to explain it, and within seconds we were engaged in an animated discussion. It turns out that the left angular gyrus contains signiﬁcantly more gray matter in bilinguals (people ﬂuent in two languages) than in monolinguals (those ﬂuent in only one language). Furthermore, the white matter underlying it is characterized by greater density. In plain English this means that there are more neurons and more connections in the left hemisphere of the individuals in command of two languages than in the people who speak only one language.
Being a bilingual (trilingual in fact, but let’s not push it), I congratulated myself on possessing a large left angular gyrus, and began to ponder the signiﬁcance of the study. Gray matter consists of neurons and the short, local connections between them. The ﬁndings suggest that extra cognitive activity triggers an increase in the number of neurons in the cortical regions doing the work. It also suggests that extra cognitive activity stimulates the growth of short, local connections between neurons.
Neurons are not born right where they perform their function. They are manufactured around the walls of the lateral ventricles as undifferentiated stem cells. Then the stem cells differentiate into specific types of nerve cells and migrate to their ultimate destinations in various parts of the brain including the neocortex, far away (in terms of brain space) from their birthplace. So it appears that neuronal migration trafﬁc is regulated, at least to some extent, by cognitive activity, which determines not only how many neurons should be manufactured but also where they should go.
But this is not all. Not only do bilinguals have more gray matter in their left angular gyrus than monolinguals, but they also have greater white matter density in the left hemisphere. White matter consists of long myelinated pathways in charge of connecting far-ﬂung cortical regions. It appears that extra cognitive activity stimulates the growth of long-distance pathways as well. This is no less important than the number of neurons, since the complex functions of the brain arise from multiple interactions between huge numbers of neurons, both nearby and far removed from one another, and such interactions are mediated by the pathways between neurons. The denser the matrix of such pathways, the greater the functional capacity of the neuronal network. What’s more, bilinguals appear to have greater white matter density than monolinguals not only in the left hemisphere but in the right hemisphere as well. This ﬁnding suggests that the right hemisphere plays a role in learning a second language, which resonates with the functional neuroimaging studies of bilingualism discussed earlier in the book.
The study is truly a gem not least because it involved both early bilinguals (who acquired the second language early in life) and late bilinguals (who acquired the second language later in life). An increase in left-hemisphere gray matter compared to monolinguals was evident in both groups of bilinguals. This means that the brain-enhancing effects of cognitive activity are not limited to young age. They continue much later in life as well.
The next study compares the size of a cortical area known as the Heschl’s gyrus in professional musicians and nonmusicians (many of us will fall into the latter category). This cortical area is critical for sound processing. And guess what—the Heschl’s gyrus is twice as large in musicians than in nonmusicians. Furthermore, the greater the intensity of practicing music in the last ten years, the greater the size of the Heschl’s gyrus. Again, the relationship between the cognitive activation and speciﬁc brain regions is apparent and striking.
And then, a few months later, an MRI study of brain changes in jugglers was reported in Nature magazine, one of the most respected science journals in the world. Healthy volunteers, none with prior experience in juggling, were trained for three months in a three-ball juggling routine. As a result of the training, the volunteers achieved enough juggling proﬁciency to keep the balls in the air for at least sixty seconds. When their before and after brain MRI scans were compared, it turned out that the amount of gray matter increased in the temporal lobes in both hemispheres and in the parietal lobe of the left hemisphere. With the interruption of practice, the effect gradually dwindled away and the gray matter gains in the parietal and temporal lobes were reduced. This was evident in the third MRI scan recorded three months after the discontinuation of juggling practice. So the effect of skill practice on neuronal proliferation in very speciﬁc parts of the brain could be demonstrated even within a relatively short period of time.
A devil’s advocate might say that musicians become musicians because they are born with a larger Heschl’s gyrus, which in turn endows them with a particular musical talent. And couldn’t it be that a natural selection occurs among the cab drivers, such that those born with larger hippocampi ﬁnd the job more agreeable because they have a better memory for complex routes? And couldn’t it also be that people born with a larger left angular gyrus have a greater natural aptitude for languages and thus learn more of them? But while biology is a major part of our destinies, the “destiny imperative” does not explain everything. It cannot explain, for instance, why the sizes of the hippocampi, the Heschl’s gyrus, and other parts of the brain are positively correlated with the amount of time spent in practicing certain cognitive skills. And it certainly cannot explain the rapid, and reversible, effect of juggling practice on the brain. These correlations indicate that ample room exists for pushing biology around, that biology sets a range of expressions (and not a ﬁxed constant) for each ability, and that exactly where within this range we end up depends on us—on what we do with our brains and with ourselves.
THE AGING HEMISPHERES AND DEMENTIA
So, by engaging in vigorous mental activities, we change our brain in ways so profound that certain brain regions may actually grow in size. The next issue to address is: which areas?
The relationship between the nature of mental activities of cab divers, bilingual people, musicians, and jugglers, and the brain structures affected by the activities described in these studies, appears to be impressively speciﬁc. In order to remove any doubt in the speciﬁcity of the cognitive-stimulation effects on the brain, neuroimaging studies would need additional rigorous controls. By this I mean the measurements of certain additional brain structures with minimal or no involvement in the cognitive activities used for brain stimulation. And one would need to meticulously show that such control brain structures did not increase in size, that only the brain structures directly involved in the cognitive activities did. But the ﬁndings reviewed earlier in this chapter offer a good start.
Let’s now step back and think about the real-life implications of all these studies. Most of us, in fact all of us, exercise certain mental faculties more than others, by virtue of doing our jobs or enjoying our hobbies. This is a pervasive, universal fact of life. The effects of learning music or learning languages, or of learning complex street routes or juggling routines, on the brain are merely cases in point, examples of a profoundly general phenomenon. To the extent that the brain-stimulating effects of mental activities are even somewhat speciﬁc—and they appear to be—they are likely to beneﬁt different brain structures in different people. But are there any invariants despite the differences? Are there any common themes dominating the brain-stimulating effects of mental activities, which rise above this sea of individual differences dictated by the diversity of our educations, occupations, and experiences?
Enter again the two cerebral hemispheres. We already know that most cognitive skills are controlled by the right hemisphere at the early stages of learning, but they are controlled by the left hemisphere once we reach a certain level of mastery. This means that with experience we increasingly rely on our left hemisphere across a very wide range of mental activities and skills, whatever these activities and skills may be in a given individual. It appears that, as we move through life, the brain structures housed in the left hemisphere become increasingly engaged compared to the brain structures housed in the right hemisphere. Therefore the left hemisphere becomes the predominant beneﬁciary of the enhancing effects of mental activities, regardless of their speciﬁc nature. (Of course, this conclusion is predicated on the assumption that the brain-stimulating effects of mental activity are at least somewhat speciﬁc, which at this point we have strong reasons to believe is precisely the case.) With this in mind, it should come as no surprise that the practice-enhancing effects of activities as diverse as language and juggling were both seen particularly in the left hemisphere.
And so, as the brain mapping conference came to a close, I had a feeling (a bit complacent, but maybe not wholly undeserved) that I have glimpsed beyond the trees at an important corner of the forest. My take-home message from the meeting was, in fact, three messages wrapped in one:
- The right hemisphere decays more than the left hemisphere as we age.
- The left hemisphere beneﬁts increasingly more than the right hemisphere from mental exercise, as we move through life.
Although not quite a formal Aristotelian syllogism, the following conclusion is warranted:
- The left hemisphere is better able to withstand the decaying effects of age because it continues to be enhanced and strengthened by cognitive activities as we age.
Earlier in the book we discussed the protective effect of education against dementia. With the knowledge available today, we may conclude with a fair degree of conﬁdence that this is probably due to the fact that educated people are more likely to make their living with their brain than with their brawn, and thus will beneﬁt more from the brain-enhancing effect of a lifetime of vigorous mental activity. And as we are approaching the end of this chapter, we may be tempted to conclude that such a protective effect will be more apparent in the left hemisphere than in the right hemisphere.
Neuroscientists studying dementias have long been perplexed by the many faces of dementia at its early stages. The early manifestations of dementia, any dementia, are extremely diverse. This is especially the case with Alzheimer’s disease. It is true that in the majority of patients the earliest manifestations of Alzheimer’s dementia start with memory impairment, but in a signiﬁcant number of such patients other functions suffer ﬁrst: language, spatial orientation, or executive functions. Several neurologists, including one of the world’s foremost experts on dementias, estimated that the earliest symptoms of cognitive decline involve memory in up to 70 percent of people eventually diagnosed with Alzheimer’s-type dementia. But in at least 30 percent of such people (a huge minority) memory decline is preceded by the decline of other functions, such as language, spatial orientation, or executive functions, with the “personality change” suggestive of frontal-lobe disease.
When the diversity of the early symptoms of Alzheimer’s disease was ﬁrst recognized, hypotheses began to promulgate that Alzheimer’s is not one disease but many separate diseases. This notion, popular in the 1980s, has since been discarded. It is more likely that the diversity of the early symptoms of dementia is the ﬂip side of the diversity of the proﬁles of neural protection offered by a lifetime of certain kinds of mental activities. These proﬁles obviously differ in individuals, depending on the nature of their lifelong activities. While some cognitive functions are exercised more (thus conferring neuroprotection on certain parts of the brain), other cognitive functions are exercised less (thus failing to confer neuroprotection on certain other parts of the brain). These latter brain structures will represent the “chinks in the armor” of neuroprotection, which will vary from person to person. Certain lifelong cognitive histories exercise particular parts of the brain more than others, and this may confer neuroprotection (albeit partial and temporary) on the exercised parts of the brain against the ravages of early dementia. This is only a hypothesis, but it is an intriguing one.
According to this logic, early dementia in a writer is less likely to affect language than spatial processes. In an architect, the disease progression will take an opposite course: language succumbing ﬁrst and spatial processed much later. In an executive in charge of strategic planning, the frontal lobes will put up the longest resistance to the effects of brain decay. But in the proverbial London cab driver, memory will be the last to go, way after language or executive functions.
The brain structures beneﬁting from the neuroprotection conferred by exercise are able to withstand the assault of neurological decay for longer, maybe for much longer. A body of evidence now exists (and is growing) that aging individuals may remain functionally and cognitively sound despite the neuropathological signs of Alzheimer’s disease and other dementias. Robert Katzman and his associates at Albert Einstein College of Medicine in New York and University of California, San Diego, studied a sample of such people and found that they had greater brain weight and more large neurons than the matched controls. It is likely that the unusually large brain weight was a reﬂection of a greater number of large neurons and pathways, which in turn was due to a lifelong history of cognitive vigor and exertion. This possibility, which even a decade ago would have been dismissed as fantastic, today ﬁnds support in observations such as those involving London cab drivers, bilinguals, and professional musicians.