Brain Rules (Updated and Expanded)

part of your brain that somehow fell off and landed in your mid-abdomen.
Stress hormones can do some truly nasty things to your brain if
boatloads of the stuff are given free access to your central nervous system.
And that’s what is going on when you experience chronic stress. Stress
hormones seem to have a particular liking for cells in the hippocampus,
which is a problem because the hippocampus is deeply involved in many
aspects of human learning. Stress hormones can make cells in the
hippocampus more vulnerable to other stresses. Stress hormones can
disconnect neural networks, the webbing of brain cells that store your most
precious memories. For example, a bodyguard was in the car with Princess
Diana on the night of her death. To this day, he cannot remember the events
several hours before or after the car crash. Amnesia is a typical response to
catastrophic stress. Its lighter cousin, forgetfulness, is quite common when
the stress is less severe but more pervasive.
Stress hormones also can stop the hippocampus from giving birth to
brand-new baby neurons. Under extreme conditions, stress hormones can

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even kill hippocampal cells. Quite literally, severe stress can cause brain
damage in the very tissues most likely to help you succeed in life.
One of the most insidious effects of prolonged stress is that it pushes
people into depression. I don’t mean the “blues” people can experience as a
normal part of daily living. Nor do I mean the grief resulting from tragic
circumstance, such as the death of a relative. I am talking about the kind of
depression that causes as many as 800,000 people a year to attempt suicide.
It is a disease every bit as organic as diabetes, and often deadlier. Chronic
exposure to stress can lead you to depression’s doorstep, then push you
through. Depression is a deregulation of thought processes, including
memory, language, quantitative reasoning, fluid intelligence, and spatial
perception. The list is long and familiar. But one of its hallmarks may not
be as familiar, unless you are in depression. Many people who feel
depressed also feel there is no way out of their depression. They feel that
life’s shocks are permanent and things will never get better. Even though
there 
is
a way out—treatment is often very successful—they have no
perception of it. The situation feels so helpless that they don’t seek
treatment. Yet they can no more argue their way out of a depression than
they could argue their way out of a heart attack. Clearly, stress hurts
learning. Most important, however, stress hurts 
people
.
The hero: BDNF
The brain seems to be aware of all this and has supplied our story not only
with a villain but also with a hero. We met this champion in the Exercise
chapter. It’s brain-derived neurotrophic factor. BDNF is the premier
member of a powerful group of proteins called neurotrophins. BDNF in the
hippocampus acts like a peacekeeping force, keeping neurons alive and
growing in the presence of hostile action. As long as there is enough BDNF
around, stress hormones cannot do their damage.
How, then, does the system break down? The problem begins when too
many stress hormones hang around in the brain too long, a situation you
find in chronic stress, especially learned helplessness. As wonderful as the
BDNF forces are, it is possible to overwhelm them if they are assaulted
with a sufficiently strong (and sufficiently lengthy) glucocorticoid siege.
Like a fortress overrun by invaders, enough stress hormones will eventually

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overwhelm the brain’s natural defenses and wreak their havoc. In sufficient
quantities, stress hormones are fully capable of turning off the gene that
makes BDNF in hippocampal cells, causing long-lasting damage. You read
that right: Not only can they overwhelm our natural defenses, but they can
actually turn them