blood vessels. These scars become magnets for molecules to accumulate,
creating lumps called plaques. These can grow large enough to block the
blood vessels. If it happens in the
blood vessels of your heart, you get a
heart attack; in your brain, you get a stroke. Not surprisingly, people who
experience chronic stress have an elevated risk of heart attacks and strokes.
Immune system
Stress also affects our immune response. At first, the stress response
helps equip your white blood cells, sending them off to fight on your body’s
most vulnerable fronts, such as the skin. Acute stress can even make you
respond better to a flu shot. But chronic stress reverses these effects,
decreasing your number of heroic white-blood-cell soldiers, stripping them
of
their weapons, even killing them outright. Over the long term, stress
ravages parts of the immune system involved in producing antibodies.
Together, these can cripple your ability to fight infection. Chronic stress
also can coax your immune system to fire indiscriminately, even at targets
that aren’t shooting back—like your own body. Not surprisingly, people
who experience chronic stress are sick more often. A
lot
more often. One
study showed that stressed individuals were three times more likely to
suffer
from the common cold, especially if the stress was social in nature
and lasted more than a month. They also are more likely to suffer from
autoimmune disorders, such as asthma and diabetes.
To show how sensitive the immune system can be to stress, you need
look no further than an experiment done at UCLA. Trained actors practiced
Method acting, in which if a scene calls for you to be scared, you think of
something frightening, then recite your
lines while plumbing those
memories. On one day, the actors performed using only happy memories.
On another day, they performed using only sad memories. The researchers
took blood samples, continually assessing their immune systems. On the
“happy days,” the actors had healthy immune systems. Their immune cells
were plentiful, happy, readily available for work. On the “sad days,” the
actors showed something unexpected: a marked decrease in immune
responsiveness. Their immune cells were not plentiful, not as robust, not as
available to protect against infection.
Memory and problem solving
Stress affects memory.
The hippocampus, that fortress of human
memory, is studded with cortisol receptors like cloves in a ham. This makes
it
very
responsive to stress signals. If the stress is not too severe, your brain
performs better when it is stressed than when it is not stressed. You can
solve problems more effectively and you are more likely to retain
information. There’s an evolutionary reason for this. Our survival on the
savannah depended upon remembering what was life-threatening and what
was not. Ancestors who could commit those experiences to memory the
fastest (and recall them accurately with equal speed) were more apt to
survive than those who couldn’t. Indeed, research shows that memories of
stressful experiences are formed almost instantaneously in the human brain,
and they can be recalled very quickly during times of crises.
If the stress
is too severe or too prolonged, however, stress begins to
harm learning. Stressed people don’t do math very well. They don’t process
language very efficiently. They have poorer memories, both short and long
forms. Stressed people do not generalize or adapt old pieces of information
to new scenarios as well as non-stressed individuals. They can’t
concentrate. In almost every way it can be tested, chronic stress hurts our
ability to learn. One study showed that adults with high levels of stress
performed 50 percent worse than adults with low levels of stress on tests of
declarative memory (things you can declare) and executive function (the
type of thinking that involves problem solving and self control). Those, of
course, are the skills needed to excel in school, at work, and in
relationships.
I remember a story by a flight instructor I knew well. He told me about
the best student he ever had, and a powerful lesson he learned about what it
meant to teach her. The student excelled in ground school. She aced the
simulations, aced her courses. In the skies,
she showed natural skill,
improvising even in rapidly changing weather conditions. One day in the
air, the instructor saw her doing something naïve. He was having a bad day
and he yelled at her. He pushed her hands away from the airplane’s
equivalent of a steering wheel. He pointed angrily at an instrument.
Dumbfounded, the student tried to correct herself, but in the stress of the
moment, she made more errors, said she couldn’t think, and then buried her
head in her hands and started to cry. The teacher took control of the aircraft
and landed it. For a long time, the student would not get back into the same
cockpit. The incident hurt not only the teacher’s professional relationship
with the student but the student’s ability to learn. It also crushed the
instructor. If he had been able to predict how the student would react to his
threatening behavior, he never would have acted that way.
Relationships
matter when attempting to teach human beings—whether you’re a parent,
teacher, boss, or peer. Here we are talking about the highly intellectual
venture of flying an aircraft. But its success is fully dependent upon
feelings.
The villain: cortisol
The biology behind this assault on our intelligences can be described as a
tale of two molecules: one a villain, the other a hero. The villain is the
aforementioned cortisol, part of a motley crew of stress hormones going by
the name glucocorticoids. These hormones
are secreted by the adrenal
glands, which lie like a roof on top of your kidneys. The adrenal glands are
so exquisitely responsive to neural signals, they appear to have once been a
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