Brain Rules (Updated and Expanded)

A measurable physiological response:
There must be an aroused
physiological response to the stress, and it must be measurable by an
outside party. I saw this the first time my then 18-month-old son

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encountered a carrot on his plate at dinner. He promptly went ballistic: He
screamed and cried and peed in his diaper. His aroused physiological state
was immediately measurable by his dad, and probably by anyone else
within a half mile of our kitchen table.
A desire to avoid the situation:
The stressor must be perceived as
aversive—something that, given the choice, you’d rather not experience. It
was obvious where my son stood on the matter. Within seconds, he
snatched the carrot off his plate and threw it on the floor. Then he deftly got
down off his chair and tried to stomp on the predatory vegetable.
A loss of control:
The person must not feel in control of the stressor.
Like a volume knob on some emotional radio, the more the loss of control,
the more severe the stress is perceived to be. This element of control and its
closely related twin, predictability, lie at the heart of learned helplessness.
My son reacted as strongly as he did in part because he knew I wanted him
to eat the carrot, and he was used to doing what I told him to do. Control
was the issue. Despite my picking up the carrot, washing it, then rubbing
my tummy while enthusiastically saying “yum, yum,” he was having none
of it. Or, more important, he wanted to have none of it, and he thought I was
going to make him have all of it. Feeling out of control over the carrot
equaled out-of-control behavior.
When you find this trinity of components working together, you have
the type of stress easily measurable in a laboratory setting. When I talk
about stress, I am usually referring to situations like these.
We’re built for stress that lasts only seconds
You can feel your body responding to stress: Your pulse races, your blood
pressure rises, and you feel a massive release of energy. That’s the famous
hormone adrenaline at work. This fight-or-flight response is spurred into
action by your brain’s hypothalamus, that pea-size organ sitting almost in
the middle of your head. When your sensory systems detect stress, the
hypothalamus signals your adrenal glands to dump buckets of adrenaline
into your bloodstream. There’s a less famous hormone at work, too—also
released by the adrenals, and just as powerful as adrenalin. It’s called
cortisol. It’s the second wave of our defensive reaction to stressors. In small

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doses, it wipes out most unpleasant aspects of stress, returning us to
normalcy.
Why do our bodies need to go through all this trouble? The answer is
very simple. Without a flexible, immediately available, highly regulated
stress response, we would die. Remember, the brain is the world’s most
sophisticated survival organ. All of its many complexities are built toward a
mildly erotic, singularly selfish goal: to live long enough to thrust our genes
on to the next generation. Our reactions to stress help us manage the threats
that could keep us from procreating.
And what kinds of survival threats did we experience in our
evolutionary toddlerhood? Predators would make the top 10 list. So would
physical injury. In modern times, a broken leg means a trip to the doctor. In
our distant past, a broken leg often meant a death sentence. The day’s
weather would have been a concern, the day’s offering of food another. A
lot of very 
immediate
needs rise to the surface. Most of the survival issues
we faced in our first few million years did not take long to settle. The saber-
toothed tiger either ate us or we ran away from it—or a lucky few might
stab it, but the whole thing was usually over in moments. Consequently, our
stress responses were shaped to solve problems that lasted not for years, but
for seconds. They were primarily designed to get our muscles moving us as
quickly as possible out of harm’s way.
These days, our stresses are measured not in moments with mountain
lions, but in hours, days, and sometimes months with hectic workplaces,
screaming toddlers, and money problems. Our system isn’t built for that.
And when moderate amounts of stress hormones build up to large amounts,
or hang around too long, they become quite harmful. That’s how an
exquisitely tuned system can become deregulated enough to affect a report
card or a performance review—or a dog in a metal crate.