Aging is the neglected stepchild of the human life cycle.
—Robert Butler
THE FIRST TIME I CRADLED A HUMAN BRAIN IN MY hands, my reaction was pure fascination. I explored the convolutions of the cortex, peered deeply into the fissure separating the hemispheres, and marveled at the cerebellum nestled below. The few pounds of neurons, glial cells, and supporting tissue I was holding once contained a person’s life: the sights, sounds, and smells of a culture, a memory of first love, and the last thoughts before death. The fact that a brain is capable of such things is almost beyond comprehension.
Until recently, it was assumed that brain growth ceased after childhood and that aging was synonymous with decay. The brain was also thought of as a static organ, like the heart and lungs, performing the same job in the same way from birth until death. Our brains, however, have been shaped by evolution to adapt and readapt to the ever-changing demands of our physical and social environments. Not only does the structure of the brain change throughout life, but so does the way it processes information. As we will see, many adaptations are tied to the changing social demands that we face during each phase of life.
Lifelong plasticity, the accumulation of knowledge, and the motivation to transmit wisdom to the next generations all contribute to the birth and growth of culture. While most social mammals have a three-stage life span (infant, juvenile, and adult), humans have at least five: infant, child, juvenile, adolescent, and adult.1 In addition, current research supports the need for multiple stages of adulthood in light of our increasing longevity and an expanded focus on the complexity of modern life.
While our general focus is on older adults, the brain is best understood in the context of its development across the entire life span. In addition to looking at the changing structures and functions of the brain, we will also consider the social and emotional challenges we face in our roles as children and parents, learners and teachers, clients and therapists. Weaving together these multiple perspectives will reflect the rich tapestry of the aging process as an evolving matrix of energy, information, and relationships. Let’s start at the beginning.
THE NEWBORN BRAIN
The principle activities of brains are making changes in themselves.
Marvin Minsky
Isn’t it amazing that some newborn animals can stand and walk on wobbly legs within minutes of birth? Unlike us, these animals don’t have the luxury of a gradual introduction to the world. They have to be ready to contribute to their own survival almost immediately by seeking shelter, finding food, or keeping up with the herd. Fortunately, our survival doesn’t depend on our ability to walk, jump, run, or climb a tree on our first day. For humans, our survival depends upon our ability to attach to and be protected by those around us. If a human child is lucky enough to be born to available, sane, and healthy parents, he or she can expect many years of healthy development.
Animals that are born ready to rock and roll (or at least walk and run) rely largely on preprogrammed brains driven by deep evolutionary instincts. In stark contrast, we humans are extremely premature, highly dependent newborns whose brains are largely shaped after birth. The evolution of our social brain is revealed in reflexes to orient toward our mother, stare into her eyes, and smile to make her interested in us. We take turns making sounds, play peekaboo, and learn the cadence and melodies of communication. Freedom from fighting for physical survival allows for a long and gradual runway for development that makes ours the most highly complex brains we know of.
During early brain development, a number of simultaneous processes occur. The first is that adjacent neurons begin to connect. In this process, neurons fire together, wire together, and form functional networks, which come to organize our behaviors, thoughts, and emotions. Nature’s strategy is to overproduce neurons and allow those that are unsuccessful in connecting with others to die off in a process called apoptosis. This neural Darwinism appears to optimize effective brain development and functioning. Apoptosis demonstrates that the normal loss of neurons is not an indication of brain disease and loss of function.
Another aspect of brain development is the emergence of connective fibers, or white matter, that link distant regions of the brain to establish complex adaptive networks. As these networks grow and interconnect with one another, electrical brain wave patterns gradually synchronize, yet another indication of brain development. The sophistication of these connections and the participation of diverse brain regions in abstract thinking and problem solving continues throughout life.
Early brain development is characterized by sensitive periods that are genetically programmed times of exuberant neural growth in specific brain networks in response to specific stimuli. In the first days of life, the visual cortex is stimulated by a flood of lights, edges, and colors as it begins to adapt to the newborn’s physical world. During the first few months, relationships shape networks of attachment and emotional regulation. Year two ushers in an explosion of language development as the left hemisphere enters a sensitive period. It is important for healthy development that we have adequate and appropriate stimulation while we are going through sensitive periods. Although the concept of sensitive periods of neural development was initially considered to apply only during early childhood, we now know that they also occur in adolescence and most likely throughout life.
THE ADOLESCENT BRAIN
Poetry is adolescence fermented, and thus preserved.
Ortega y Gasset
Until recently, the scientific dogma was that the brain was relatively fixed after the first few years of life. It was clear that it grew larger and that we learned more information, but these changes were seen as a matter of quantity rather than quality. But when researchers began to take a closer look at adolescent brains, they were amazed by the amount of neural upheaval they found. They found considerable plasticity and reorganization taking place in the frontal lobes from the onset of puberty into the early 20s. Once this was discovered, it became obvious that the psychological and social upheavals of adolescence coincided with a previously unrecognized sensitive period of neurological maturation. This now seems obvious and has become the new dogma.
For most of our evolutionary history, humans were considered adults by their mid-teens and were expected to mate and begin to have children of their own. Consider the challenges that adolescents face. They need to establish a social identity, connect with a peer group, and create new boundaries with their families—powerful drives from our Paleolithic mandates. These challenges require reshaping of attachment bonds as they move from being passive recipients of care to caretakers. Adolescents have to break with the values and structures of their family of origin and become desirable to comrades, mates, and peers, simultaneously transferring sources of emotional security outside the immediate family.
These new demands require extensive plasticity in the prefrontal cortex to accommodate so much social upheaval and problem solving. So while your teenagers may be making you crazy, it’s no picnic for them either. These radical changes in the brain parallel the sheer rawness of youth—the sudden mood swings, intense passion, and that all-encompassing feeling that you are alone in a vast and hostile world. To make things even more challenging, modern culture has prolonged childhood for an extra decade so that the impulse to be an adult slams into the expectations of conformity and obedience expected of children at home and at school.
The biological and social revolutions of adolescence are not without their dangers. Driven by rising hormones and compromised emotional regulation, the prefrontal cortex is destabilized, making judgment and insight less than stellar. What adolescents lack in perspective, they attempt to compensate for with energy, emotion, and a can-do spirit. While necessary for many of the challenges adolescents once faced as hunter-gatherers, these qualities are poorly matched to the demands of the modern world.
Adolescents become intoxicated with a feeling of invincibility while simultaneously suffering from impairments of judgment and impulse control—a toxic combination. Just check the car insurance rates for teenage drivers and how their risk of having an accident soars when they are “under the influence” of driving with their peers. The gradual decrease of insurance rates into adulthood parallels the increase in brain development that leads them to better judgment and impulse control. Those of us who marvel at how we survived adolescence cringe at the thought of our own adolescents let loose in the world.
Reward systems, such as those mediated by dopamine, also destabilize during adolescence to drive new attachments, passions, and goals. The strong drive to find their purpose and meaning makes adolescents more vulnerable to both good and bad social influences, peer pressure, and destructive cults.2 Many become vulnerable to increased risky behaviors, eating disorders, and addictions.3 Tobacco and alcohol companies are well aware of this vulnerability and spend vast amounts of money to convert teenagers into lifelong customers. While the sensitive period of adolescence was selected to get young people passionate about starting their own lives and contributing to the tribe, it puts them at risk in our modern world.
From adolescence through early adulthood, brain development continues with structural changes that parallel advances in language, judgment, impulse control, and emotional regulation.4 Just as in early childhood, individual neurons continue to be eliminated as the brain’s neural networks become more efficient in their functioning.5 The brain is on its way to peak performance in areas of speed, motor coordination, and sensory acuity. Historically, these strengths contributed to tribal survival through hunting, fighting, and mating. As we near the end of adolescence and move into adulthood, enhanced communication, integration, and inhibition among different neural networks lead to increased speed of abstract functioning, and improved emotional regulation and problem-solving abilities.
THE ADULT BRAIN
Forty is the old age of youth; fifty the youth of old age.
Victor Hugo
Through our 20s, the hormonal, neural, and social upheavals of adolescence gradually settle down. The prefrontal cortex continues to mature and connect with other regions of the brain.6 We see a more streamlined and efficient brain that performs better because of increased organization and greater hormonal and emotional stability. The dorsal and lateral regions of the prefrontal cortex and the parietal lobes mature and interconnect with the rest of the cortex, supporting higher levels of imagination and abstract thinking. We also see improvements in planning, spatial memory, and long-term memory.7
During young adulthood, especially in males, lateral specialization in the frontal lobes reaches its peak. This increasing specialization involves the active inhibition of brain regions in the other hemisphere that could do the same job but less efficiently.8 This processing strategy reflects the choice by natural selection of speed over deliberation at this stage of life. Keep in mind that lateral specialization reverses later in adulthood as the brain adapts to new roles in which deep thinking is crucial and speed is not. At the beginning of adulthood, speed and efficiency trump reflection and long deliberation.
In midlife, the number of neurons within the cortex continues to decrease while subcortical structures appear to stabilize. Although neuronal loss is almost always interpreted as reflecting declining function after young adulthood, there is no definitive evidence that this is true for healthy adults. From childhood through adolescence and into young adulthood, apoptosis continues to be a normal aspect of brain maturation associated with increasing abilities.9 The space once occupied by excess neurons becomes filled with glial cells and chemical compounds that enhance neural processing capabilities.10 In contrast to earlier adulthood, we see increases in the volume of white matter into midlife, with a gradual decrease thereafter. This loss of white matter may have little impact or may serve to lessen the efficiency of coordination among brain regions.11
If this increasing participation of multiple brain regions is an adaptive strategy from childhood onward, shifts in white matter may be a functional aspect of the aging brain. Slower, more inclusive, and more thoughtful processing develops as we grow older, likely serving the increased synthetic knowledge and problem-solving abilities traditionally expected of tribal elders. In fact, when brain activity is measured by the complexity of electrical activity, there is an increase from childhood into the 60s, the highest age measured.12 Table 5.1 summarizes the structural brain changes during midlife.
Table 5.1. Structural Changes in the Brain During Midlife
| Gray Matter Changes | Effects |
| Decreases in the density and volume of cortical gray matter | Neural systems become more focused, specific, and efficient later in life a |
| Posterior temporal lobe volume increases until age 30, then decreases | This may reflect the initial increase and subsequent slow decline in processing and remembering external events b |
| Subcortical volume loss is much less pronounced during aging | |
| White Matter Changes | |
| Increases in volume until midlife and decreases thereafter | Subcortical structures are more stable with less emotional variationc |
| Continuing integration of neural systems until 40–50 years of age with increases in problem solving d |
As we shift our focus from measures of overall brain volume to specific areas and networks, we find that aging is not uniform. Generally, brain networks that evolved most recently and develop most slowly during childhood and adolescence show earlier signs of aging.13 Remember that the dorsal and lateral areas of the prefrontal lobes (DLPFC), which continue to mature through adolescence and into our 20s, show the earliest signs of decline. White matter tracts connecting these regions to temporal and hippocampal structures show early signs of volume loss, likely contributing to decreases in short-term memory.14 This is why for most of us, no matter how wise we may grow over the years, it gets harder to recall peoples’ names, find where we parked the car, and remember that our glasses are on our heads.
Declines in executive function, explicit memory, and attention processed by the DLPFC are in stark contrast to the OMPFC systems that specialize in attachment and emotional regulation. The retention and even improvement of social judgment and empathy reflect the continued health and development of brain networks associated with the OMPFC.15 Solid social judgment relies on the accumulation of experience, thoughtful consideration, and emotional maturity. Although there may be a decreased need for new learning and quick reactions as we age, natural selection found sustained attachment and emotional stability to be worthy of the investment the body continues to make in the social brain throughout life.
THE OLDEST OLD
Growing old is no more than a bad habit which a busy person has no time to form.
André Maurois
In 1962, there were 1,500 centenarians in the United States. By 1995, the U.S. Census Bureau counted 50,000 and predicted this number to rise to 1,000,000 by 2050.16 By that time, people over 85 will be the fastest-growing age group in society. The belief that increases in the population of the oldest old will be a drain on society is based on the idea that they will suffer from more diseases and disabilities as they age.
In reality, the oldest old are in pretty good shape. Many healthy older adults show no signs of significant brain volume loss past 100 years of age.17 The most common explanation for this phenomenon is that those people who live to their mid-90s are particularly resistant to diseases that killed the others in their age group. Because of their robustness, they not only outlive others, but do so with relatively few disabilities. Many of the oldest old, like Madame Calment, lead active, healthy lives with short periods of illness and infirmity before passing away.
In contrast to younger-old adults, where women are generally healthier, the oldest old are typically men who are mentally and physically healthier than women. This is a by-product of the fact that men with dementia and other disabling illnesses tend to die from them earlier, while women survive despite these illnesses. The first signs of this gender crossover can be seen at the age of about 80 years. In a study at the National Institute of Aging, it was found that 44% of the men in that age group were robust and independent compared with only 28% of women.18 While the currently available data are inadequate to draw conclusions, we can guess that the brains of the oldest old have a great deal to teach us about positive aging.
THE EVOLUTION OF SOCIAL ANIMALS
Realize that you will live several lifetimes. You may be one person at 20, another at 60, and another at 80.
Lena Horne
The coevolution of the human brain with caretaking, attachment, family, and culture suggests that our social roles and responsibilities should be a central focus in understanding healthy aging. Our increasing understanding of how epigenetics translates experience into neural structure suggests that our experiences trigger many brain-building processes throughout the life span. For example, as many as 540 genes related to brain-based events have been shown to have different activation patterns at different times of life.19 It is logical to assume that the expression of some of these genes may be triggered by the brain’s response to changes in social roles and relationships. In other words, our biologies may utilize the flexibility of transcription genetics to maximize functioning in response to changing social challenges throughout life.
Just as presenting a virgin rat with a rat pup stimulates areas of her brain to grow, being needed, respected, and admired activates neural plasticity and brain growth in older human adults. Research with zebra finches has shown that their ability to learn their songs is enhanced when exposed to live singing birds versus tape recordings of the same birdsong.20 Some are actually unable to learn from tape recordings and require positive interactions with a teacher to stimulate the brain.21 Similarly, there is something about positive relationships that help humans to learn. The opposite is also true—have you ever tried to learn something new in the presence of a critical onlooker?
A caring, supportive other creates a state of mind and body that primes our internal biology for new learning—call it a pro-plasticity state of mind. We often see that high-risk children and adolescents who eventually have successful lives had at least one person who took an interest in them—a mentor, teacher, or coach—someone who gave them time, believed in them, and encouraged their success. This is not to be taken lightly; it points to the fact that, like birds learning their song, we may learn better face to face and heart to heart. If social interactions and neuroplasticity are synergistic, it is clear why elders who become isolated are more likely to lose cognitive functions. On the other hand, those that remain connected, challenged, and needed are far more likely to remain vital and alive. Isolation and lack of stimulation are the enemies of a healthy brain at any age.
In addition to adaptations to changing social demands, it is also likely that we need to adjust to the changing realities of our bodies. Let’s assume that as we age, the body is less able to produce energy. Less energy presents an adaptational challenge—how shall resources be allocated to optimize functioning? Like someone operating an energy grid, decisions have to be made concerning where to channel energy, where to cut it off, and where to turn it down. Hospitals and airports may have high priorities, while casinos and playgrounds end up in the dark. Could a similar adaptational challenge face the brain during aging?
Let’s say that our brains have to make do with 10% less energy each decade after we turn 40. Where would the cuts be made and how would the remaining energy be deployed? Obviously we would have to maintain those vital brain stem functions that keep us alive. These circuits would be like our hospitals and airports. Other than these life-sustaining processes, all other circuits would be subject to energy cuts. With age, competent brains may adjust to changes in energy availability by diminishing the functioning of some less vital networks and employing alternate ways of processing information.
By midlife we have usually mated, built a nest, and created a foundation for our sustained survival. Given that we have traditionally lived in close social groups where younger people were present to do the hunting, gathering, and fighting, perhaps older adults were shaped for different roles and contributions to the tribe. Maintaining resources dedicated to attachment, affect regulation, and caretaking supports continued social interaction, nurturance, and participation in the social economy. As we will see, the bias toward retaining old memories and the impulse to tell stories points to the role of the elder as the storehouse of culture, memory, and wisdom.
Think about the elder’s need to connect and contribute and the child’s need to be seen, loved, and encouraged. This is a naturally occurring cycle of birth and renewal that is often missed in modern society. The loss of the extended family has taken with it millions of years of natural selection that contributes to the development and well-being of all generations. The atomization of families may contribute to many problems, from more physical illnesses to school failure, for which we turn to drugs, consumerism, and other distractions in order to cope.