Beware of false knowledge; it is more dangerous than ignorance.
—George Bernard Shaw
THE MYTH ABOUT OUR BRAIN’S JOURNEY THROUGH life is a sad tale of decline; this turns out to be wrong. In addition to the complexity of the brain’s structure and organization, age-related changes are also influenced by past experience, education, physical and emotional health, and the task at hand.1 A deeper and more sophisticated look into the human brain reveals a universe of interacting neural networks and millions of connecting fibers. In fact, the brain is a sophisticated government of specialized systems that combine to perform increasingly complex tasks as we mature.
Depending on what you are doing (e.g., looking, walking, talking), different neural networks become activated and engaged, each with their own areas of expertise, gender differences, and pattern of age-related change. The brain is not a monolithic structure, and it changes during our lifetimes in complex ways; some skills and abilities improve, and some get worse, while others remain the same. Research with healthy older adults usually reveals better memory functioning than our prejudices would lead us to expect.2 Let’s begin with some basics of how the brain learns.
MEMORY AND LEARNING
By the time you’re 80 years old you’ve learned everything. You only have to remember it.
George Burns
Our ability to learn and remember is dependent upon modifications of the brain’s architecture and chemistry in a process known as neural plasticity. Plasticity is a general term describing the ability of the nervous system to change in response to experience.3 Neural plasticity also includes the growth of new neurons (neurogenesis) and the strengthening of the connections between neurons, known as long-term potentiation. Learning depends upon many layers of biochemical processes that support and maintain the brain’s ability to react to and store information from new experience.4 In this manner, the architecture of our brain becomes a physical manifestation of our experiences.
Whether an infant is learning to find her thumb, a high school student is studying history, or a grandparent is learning to use e-mail for the first time, the same neuroplastic processes occur. There is solid evidence in both animals and humans that learning triggers the brain to grow. When animals are raised in complex and challenging environments, their brains grow larger and have larger neurons, more synapses (connections among the neurons), and greater amounts of neurotransmitters and growth hormones.5
Research with animals has shown that new learning has the ability to mend earlier deficits. For example, adult rats exposed to training, stimulation, and enriched environments have demonstrated a reversal of earlier nervous system damage and genetically based learning deficits.6 These sorts of positive changes have also been seen in the recovery behaviors of neglected children who are adopted into loving families. These findings speak to the marvelous flexibility of the mammalian nervous system and suggest that the challenges we take on later in life can have a profoundly positive impact on our brains.
THE LIFE OF THE FRONTAL LOBES
Long whiskers cannot take the place of brains.
Russian proverb
Theories that focus on the loss of cognitive abilities as we grow older point to the frontal lobes as the main culprit. This perspective is based in studies that show greater neural loss, decreased activation, and less dopamine availability in the frontal lobes with age.7 But as I mentioned earlier, the brain is made up of a complex government of systems, and the frontal lobes are no exception. Let’s focus on the front-most portion of the frontal lobes, known as the prefrontal cortex.
The prefrontal cortex can be divided into two general regions—those on the top and sides (dorsal and lateral), and those on the bottom and in between the two hemispheres (orbital and medial). Let’s call these two regions the dorsolateral prefrontal cortex (DLPFC) and the orbitomedial prefrontal cortex (OMPFC), which you’ll remember from an earlier chapter. Each area connects with many other regions of the brain to perform a wide variety of tasks.
The DLPFC connects with the rest of the cortex and the hippocampus to combine attention, sensory information, imagination, and problem solving. This is one of the primary systems in the human brain that appears to differentiate us from other primates. As I mentioned earlier, the OMPFC participates in networks with the amygdala, which organizes emotional processing, fear regulation, attachment, and the experience of self. The communication between the DLPFC and OMPFC allows us to integrate thinking with feeling and to link our inner experience with the outer world.
The DLPFC, which arose later in our evolutionary history, develops slowly over the first two decades of life and begins to decline in our late 20s. In stark contrast, the OMPFC evolved much earlier, develops earlier in life, and is maintained throughout life. So while we find it harder to remember new information as we progress through adulthood, the strength of our attachment to others stays as strong as ever as our emotional stability and self-knowledge increase.
When we look more closely, we find that age-related deficits in cognitive testing are generally those dependent on the DLPFC, not the OMPFC.8 Everyday problem solving and verbal abilities seem to improve, while performance on pencil-and-paper tests reliant on speed and new learning declines after middle age.9 So while it’s true that we don’t do as well on tasks of working memory over time, our emotional and relational abilities—which cognitive psychologists almost never measure—actually get better.
The same thing is true for memory. We generally think of memory as a single function, but, in fact, we have many different forms of memory that are processed in separate neural networks. For example, you may not remember a phone number, but your hand might maintain the memory for the set of movements required to press the correct numbers. Another good example is that older adults are as good at remembering faces as the young but not as good at remembering their names.10 This is because the memory for faces involves the OMPFC, which is maintained with age, while the memory for words relies on the DLPFC.
The two general categories of memory are explicit and implicit. Explicit memory is best described as the realm of the DLPFC—conscious memory for names, places, and events. Implicit memories, the specialty of the OMPFC, do not require conscious awareness and may include early attachment experiences and trauma. Another kind of implicit memory that doesn’t require conscious reflection is procedural memories such as knowing how to ride a bicycle or play a musical instrument. In contrast to explicit memory, procedural and emotional memory are relatively unimpacted by aging because they are organized in systems that don’t experience age-related decline.11 The take-home message is that whenever someone is talking about changes in memory, we have to ask, “Memory for what?”
STRESS AND MEMORY
The mind is its own place, and in itself, can make a heaven hell, a hell of heaven.
John Milton
J. B. S. Haldane, the founder of the fields of biochemistry and genetics, examined the problem of aging in his book New Paths in Genetics.12 Haldane proposed that aging results from neglect on the part of natural selection. That is, aging is an accumulation of destructive genes (such as those for Huntington’s disease) that escape the knife of natural selection because they impact us after our childbearing years.13 Eleven years later George Williams suggested that aging is the cost of the energy required for earlier survival and reproduction.14 Neither of these theories has found consistent support.
As far as anyone knows, there is no biological mandate for just how long an organism can live.15 The longevity of any species appears to be the product of thousands of genetic, biological, and environmental variables. Thus, life spans vary from species to species; rats live for about 30 months, and humans live 70 to 80 years, while trees can live for centuries. There are even a number of single-celled organisms that are thought to be immortal. In fact, most of the neurons we have when we die were present when we were born and are still functioning just fine. Neurons most often die as a result of inadequate oxygen and nutrition or the buildup of internal waste products that interfere with their functioning. Neurons do not appear to have a definite life span.
Scientists have found that the longevity of certain species can be quickly modified. Removing the adrenal gland (and the stress hormones it generates) of the king salmon doubles its life span from 4 to 8 years, while the introduction of a specific parasite on its gills can increase its life span to 13 years.16 In both cases, the biochemistry of the salmon is changed in ways that decrease the negative impact of stress hormones on its physical well-being.
The impact of stress on humans is well documented. A dramatic example is the decline in life expectancy in Russia since the fall of communism in 1990 and the ensuing years of chaos and uncertainty.17 Thus, it is not just our genes that determine our life span, but factors such as culture, lifestyle, the quality of our relationships, and anything else that causes or decreases stress. The question of human longevity reaches beyond our genes to our language, our culture, and the minds with whom we are linked.
Our more recently evolved cortex sits atop and is interwoven with the primitive neural systems for danger (fight-flight) conserved from our reptilian ancestors. A key component of this system is the release of cortisol, a hormone involved in shifting our functioning from long-term maintenance to a focus on immediate survival. While cortisol makes energy available for emergency situations, it also results in a shutdown of the protein synthesis required for both neuroplasticity and immunological functioning. It is especially toxic to the brain’s center for new learning, the hippocampus.18
Cortisol triggers hippocampal neurons to work harder and harder until they actually run out of energy, collapse, and die.19 In addition, since cortisol impedes the synthesis of protein in the brain and body, stress may result in decreased neurogenesis and neural growth.20 In either case, the result might be deficits in our ability to fight off disease and learn new information.21 This process is especially detrimental to children and adolescents as it impedes their neurological, psychological, and social development.
The hippocampus is not only vulnerable to cortisol, but also to lack of oxygen. Mountain climbers and divers who experience periods of lower oxygen availability demonstrate hippocampal shrinkage and memory deficits. A natural part of aging is a decrease in the integrity and efficiency of the small capillaries that bring oxygen to the brain, which would contribute to hippocampal cell loss. Thus, some memory loss can be caused by vascular deterioration.22
Although a decline in explicit memory is a common feature of aging, we have no way of knowing whether it is necessary. The hippocampus does not appear to automatically lose neurons based specifically on aging. In fact, the size of temporal lobe memory areas is maintained until very late in life.23 It appears that deficits in learning and memory are the result of multiple processes that can damage hippocampal structure or impede its proper functioning.24
COGNITIVE RESERVE
Old age is like everything else. To make a success of it, you’ve got to start young.
Theodore Roosevelt
Performance on any specific cognitive task requires the activation of specialized areas and the inhibition of others that might hinder efficient processing. From adolescence onward, we tend to use more and more of our brains to solve problems. It has been shown that older subjects activate regions of social and emotional processing even when they are asked to engage in tasks that don’t require them. This leads them to perform more slowly and less well than their younger counterparts.25 This evolutionary age-related bias may lead older folks to use more of their brains than necessary for more straightforward tasks.26
Declines in basic sensory, motor, and balance functions also take a toll on brain functioning. The more attention it takes to navigate the environment—seeing through clouded lenses and walking on creaky limbs—the less we have available for cognitive functioning in other areas.27 This may be why older adults perform as well as younger adults on some memory tasks but require more time, as previously automatic processes come to require greater effort.28 In fact, as we age, tests of visual memory result in an increased activation of brain areas not activated in younger adults.29 Because the neural networks involved in cognitive processing are interwoven with those dedicated to sensory and motor function, age-related declines in these basic abilities have an adverse effect on cognitive processing.
Cognitive reserve is a hypothesis that may help us understand why some older adults are better able to cope with the effects of aging and brain disease than others. The basic theory states that the more neural structure a brain has, the more complex its organization and the more resilient it will be to the negative effects of aging and injury. It is believed that the cognitive declines associated with even healthy aging are related to the gradual degeneration of dendrites, neurons, and the biochemical mechanisms that support neural health and plasticity.30 This implies that, the more neural material you have built throughout life, the more you can afford to lose while still functioning competently.31
People with larger cognitive reserves are thought to be those who have had a better diet, higher-quality education, and more challenging jobs.32 Factors such as larger brain size, early learning, and greater occupational attainment also seem to mitigate against the effects of Alzheimer’s disease, traumatic injury, and the general impact of brain aging.33 Studies have found that expected age-related intellectual decline can be halted or reversed in many older adults by increasing environmental and social stimulation.34 The most efficient explanation would be that these experiences correlate with biological processes that enhance plasticity, creating more elaborate, complex, and flexible brains.
A number of studies, including Dr. Snowdon’s research with the sisters of Notre Dame, suggest that those who have had more education and more challenging occupations tend to have brains that age better and resist the onset and progression of dementia. Snowdon and his colleagues found that measures of cognitive function in the nuns at age 22 were associated with reduced brain weight, cerebral atrophy, and symptoms of Alzheimer’s disease more than half a century later.35 In other words, the better the nuns functioned in early adulthood, the healthier their brains were near the end of life.
About 25% of older individuals exhibiting no symptoms of Alzheimer’s disease while alive show significant Alzheimer’s-related brain pathology upon autopsy.36 Individuals with more education had a significantly greater amount of plaques and tangles in their neurons yet functioned as well as others with less advanced disease.37 This suggests that individuals with more education can sustain a greater amount of neural damage and still maintain the same level of cognitive functioning as those with less education.
Skills most dependent upon frontal functions, such as the verbal fluency and abstract thinking demanded by high-complexity occupations, appear to strongly contribute to cognitive reserve.38 Unfortunately for me, being a college professor does not protect against brain aging, although it may slow down some of its manifestations.39 Although cognitive reserve is thought to account for only 5% of our ability to predict brain health, building our brains through stimulating activities is something we know that we can do to support brain health.40
THE PRIVILEGE OF AGE
Anyone who stops learning is old, whether at 20 or 80.
Henry Ford
Age has its privileges, or so the saying goes. After raising a family, taking care of our parents, and decades of toil, we have earned the right to sit back and relax. We can say no to things that are challenging, make us uncomfortable, or require too much effort. “Let’s vacation at the same place each year; it’s comfortable and predictable, and we know where to find what we need. Let the kids figure out how to work the computer, surf the internet, or program a new cell phone. To hell with meeting new people—I already have enough friends.”
Indeed we have earned this right, but keep in mind how the brain interprets these attitudes and behaviors: “Relax—you don’t need to grow new neurons, build new dendrites, or create new connections. In fact, we can probably cut back on energy going to the brain and channel it elsewhere.” There is a type of sea barnacle that is born with a brain that has only four functions: (1) direct motion in the water, (2) detect a source of food, (3) attach to a stationary object like a rock or pier, and (4) have yourself digested. That’s right, the brain is a metabolically expensive organ, and if it’s no longer needed, it can atrophy or, in the case of the sea barnacle, trigger a self-destruct program.
Centrally related to the privilege of age is the avoidance of anxiety and risk taking. And while high levels of anxiety are to be avoided, moderate anxiety connected with the excitement of learning something new, meeting new people, or landing in an unfamiliar country can be especially good for your brain. In fact, mild anxiety in response to stimulating challenges serves as a signal to the brain: “Kick up neuron production, stimulate metabolism, and let’s make some new connections.” This positive excitement can be confused with anxiety, but it is something our brains need to stay alive. Unfortunately, many lose the ability to differentiate between positive and negative anxiety and become increasingly avoidant of any kind of challenge.
Perhaps positive arousal should be renamed “stimulation” because this is precisely the result within our brains. The brain was designed to change, so the old adage “use it or lose it” has a great deal of neural validity.41 The aging brain retains the capacity to grow in an experience-dependent manner and has to be stimulated by environmental, relational, and internal challenges.42 Being in a position where we have to solve problems stimulates our brains, telling them to stay alert, pay attention, learn, and grow.
Given the importance of continued bonding and attachment, one of the most important directions in which to orient our exploration is toward those around us. It is vitally important that we remain curious about who our children and grandchildren are and that we continue to play and remain open to imagination. What we have learned about neural plasticity tells us that the brain is primed to grow in states of safety, positive excitement, shared openness, and exploration. These states of mind create the flexibility that allows us to adapt to our children and help them discover their inner worlds. Attunement, secure attachment, curiosity, affect regulation, and brain plasticity walk hand in hand. This is as true in the first days of life as it is after a century. In Buddhism, what is known as beginner’s mind is a way to look at the world as if for the first time, with interest, enthusiasm, and engagement. This may be the optimal state of mind for a healthy brain.