Read Welcome to Your Brain Online
Authors: Sam Wang,Sandra Aamodt
Tags: #Neurophysiology-Popular works., #Brain-Popular works
and focus on the task at hand in spite of distractions. Problems with executive function begin later, for
most people when they reach their seventies, and include the deterioration of basic functions like
processing speed, response speed, and working memory, the type that allows us to remember phone
numbers for long enough to dial them. Difficulties with executive function, along with navigation
problems, explain why your grandfather doesn’t drive as well as he used to. (It’s probably just as
well that he can’t remember where he put his car keys.) Some sensory inputs decline with age, like
the hearing problems we discussed in
Chapter 7.
It also gets harder to control your muscles, though
it’s not clear whether this problem lies with the brain or with the aging body.
Practical tip: How can you protect your brain as you get older?
The most effective approach to keeping your brain healthy with age turns out to be
something you probably wouldn’t expect: physical exercise. Neurons need a lot of support
to do their jobs correctly, and problems with an aging circulatory system can reduce the
blood supply that brings oxygen and glucose to your brain. Regular exercise, of the type that
elevates your heart rate, is the single most useful thing you can do to maintain your
cognitive abilities later in life.
Elderly people who have been athletic all their lives are much better at executive-
function tasks than sedentary people of the same age. This relationship could occur because
people who are healthier tend to be more active, but that’s not it. When inactive people get
more exercise, even in their seventies, their executive function improves in just a few
months. To be effective, exercise needs to last more than thirty minutes per session and
occur several times a week, but it doesn’t need to be extremely strenuous. (Fast walking
works fine.) The benefits of exercise seem to be strongest for women, though men also
show significant gains.
How does exercise help the brain? There are several possibilities, all of which could
contribute to the effect. In people, fitness training slows the decline in cortical volume with
age. In laboratory animals, exercise increases the number of small blood vessels
(capillaries) in the brain, which would improve the availability of oxygen and glucose to
neurons. Exercise also causes the release of growth factors, proteins that support the
growth of dendrites and synapses, increase synaptic plasticity, and increase the birth of
new neurons in the hippocampus. Any of these effects might improve cognitive
performance, though it’s not known which ones are most important.
Beyond normal aging, exercise is also strongly associated with reduced risk of
dementia late in life. People who exercise regularly in middle age are one-third as likely to
get Alzheimer’s disease in their seventies as those who do not exercise. Even people who
begin exercising in their sixties can reduce their risk by as much as half. See you at the gym!
Specific changes in the brain’s structure and function are associated with the deficits in memory
and executive function during aging. The hippocampus becomes smaller with age, and this decrease in
size correlates with memory loss. Similarly, the prefrontal cortex is important for working memory
and executive function, and it becomes smaller with age as well.
Contrary to what you might imagine, brain shrinkage with aging is not due to the death of neurons.
As you age, you do not lose neurons. Instead, individual neurons shrink. Dendrites retract in several
regions of the brain, notably parts of the hippocampus and the prefrontal cortex. The number of
synaptic connections between neurons in these areas decreases with age in most animals that have
been examined. Older animals also have specific deficits in synaptic plasticity, the process that
drives learning (see
Chapter 13)
, but only in certain parts of the brain.
On the other hand, some brain functions are not influenced much by age. Verbal knowledge and
comprehension are maintained, and may even improve, as we get older. Vocabulary is another area
that tends to be spared by aging. Professional skills are typically resilient, especially if you continue
to practice them. Similarly, people who practice physical skills regularly are more likely to maintain
them; in this case, there is some evidence that experts develop new strategies for well-rehearsed
tasks to compensate for cognitive decline as they age. In general, anything that you learned thoroughly
when you were younger is likely to be relatively spared by aging.
Did you know? I’m losing my memory. Do I have Alzheimer’s disease?
If you forget where you put your glasses, that’s normal aging. If you forget that you wear
glasses, then you probably have dementia. A disorder like Alzheimer’s disease, which
causes two-thirds of the cases of dementia, is not an extreme example of regular aging, but
involves deterioration of specific brain regions along with symptoms that never occur in
normal aging. People with advanced dementia cannot remember important incidents from
their own lives and may not even recognize their spouses or children.
The strongest risk factor for Alzheimer’s disease is simply age. The incidence of the
disease doubles every five years after age sixty, reaching almost half the population by age
ninety. Statistical estimates suggest that about 75 percent of people in the U.S. would
develop Alzheimer’s disease if we all lived to be one hundred. As the world’s population
ages, dementia is becoming more of a problem; its current incidence is twenty-four million
people worldwide, and the number is expected to increase to eighty-one million by 2040.
Genetic factors have a considerable influence on your susceptibility to dementia,
particularly the age of its onset. About a dozen genes have been identified as risk or
protective factors, but one of them, the ApoE gene, has a stronger effect than all the rest put
together. The average age of onset is about fifteen years earlier for people with two copies
of the risky form of the ApoE gene compared to people with the protective form of the gene.
Many of the lifestyle factors that influence brain function during normal aging are also
relevant to Alzheimer’s disease. As discussed above, exercise is strongly protective. Other
factors that correlate with a reduced chance of dementia include education, regular
consumption of moderate amounts of red wine (but not beer or hard liquor), and the use of
over-the-counter pain relievers with anticlotting effects, like aspirin and ibuprofen. In
general, it seems as though improving your brain’s ability to function tends to improve its
resistance to a variety of problems, including dementia, late in life.
The good news is that older people have one important advantage over the young: a better ability
to regulate their emotions. The frequency of negative emotions decreases with age until it levels off
around age sixty, while positive emotions remain about the same. As people get older, they become
less likely to perceive negative events or to remember those from their everyday lives or the past.
Negative moods pass more quickly in older adults, and they are less likely to indulge in name-calling
or other destructive behavior when they’re upset.
There are also some more general changes in brain activity during aging. Older adults tend to
activate more distinct brain areas than young adults while performing the same task. Compared with
young adults, older people also tend to show lower overall brain activity and use areas on both sides
of their brains instead of just one. These findings suggest that people use their brains differently as
they age, even though they may perform a task equally well. This may be because older people learn
to use new parts of their brains to compensate for problems elsewhere.
Cognitive decline at a certain age is not inevitable. Your lifestyle has a lot of influence on your
abilities late in life. We mentioned before that people tend to retain skills and knowledge they learned
thoroughly when they were younger. Perhaps for this reason, educated people have better cognitive
performance with age than less-educated people. Another way to keep up your cognitive performance
is to have intellectually challenging hobbies. This effect is more pronounced in blue-collar workers
than in highly educated people, perhaps because educated people tend to work in jobs that involve
considerable intellectual stimulation.
Did you know? Are you born with all the neurons you’ll ever have?
Many of us learned in school that the brain is unique because, unlike other organs of the
body, it doesn’t add new cells over its lifetime. Scientists believed this for many decades,
but new discoveries indicate that it’s not true. Both animal and human studies show that a
few parts of the brain do produce new neurons in adulthood, though this ability declines
with age. In particular, new neurons are born in the olfactory bulb, which processes smell
information, and in the hippocampus. More of these new neurons survive and become
functional parts of the brain’s circuitry in animals that are learning or animals that exercise
a lot. At present we don’t have much information on the environmental conditions that
encourage this process.
Attempts to improve cognitive skills in the elderly through training have yielded mixed results.
Although most training programs work to some extent, the gains tend to be specific to the trained task,
leading to little improvement in brain function across tasks. On the bright side, though, these gains can
last for many years in some cases. One way to get around the problem of task specificity is to practice
a variety of skills—either formally or by staying involved in several hobbies or volunteer projects in
retirement. Our strongest suggestion, though, is to exercise consistently (see
Practical tip: How can
you protect your brain as you get older?
), as keeping your heart in good shape has general positive
effects on the brain, particularly on executive function, which helps you perform a variety of mental
activities.
It seems that the Greeks were onto something when they recommended that people aim for a sound
mind in a sound body. You’ll be doing your best to keep your brain healthy if you keep some of both
types of activity in your life. If you already get enough exercise, add an intellectual hobby like
learning a new language or playing bridge. If you have an intellectual job, get a physical hobby like
playing tennis or jogging. In general, having both physical and intellectual interests is the best
protection against losing brain function with age.
Is the Brain Still Evolving?
New technologies in transportation, medicine, electronics, communications, and weaponry have led
to tremendous changes in our lives and habits over the last hundred years. Public health initiatives,
vaccination, and sanitation have increased life expectancy by decades. Jet travel and communication
have made the world a smaller place. Telecommunications and the Internet have made unprecedented
amounts of information available to anyone, almost anywhere. Mass entertainment, with its constant
stimulation, has become a major part of daily life. These advances have changed how we experience
the world. Is the human brain also changing to keep pace?
Brains can change over time in two ways. First, the environment can influence brain development,
leading to rapid changes, even within a generation. Second, there is biological evolution, which
requires at least one generation to cause changes.
Rapid changes can be driven by the direct biological effects of a new environment. For instance,
children growing up in preindustrial England faced challenges such as disease, nutritional
deficiencies, and difficult field labor. After the Industrial Revolution, these were replaced by
problems such as factory labor conditions, urban living, and pollution. Living conditions changed
again and again through the Edwardian era, World War II, and the Cold War. Now children in
developed countries grow up with standardized schooling, better nutrition, mass entertainment,
computers, cell phones, and other technology.
Some of these changes in environment may underlie the Flynn effect, a phenomenon first noticed