Rewire Your Brain: Think Your Way to a Better Life

tame
rather 
than
shut down
, because you need the amygdala. It contributes to 
emotional responsiveness in general, not just fear. You don ’ t want 
to shut it down; rather, you want it to work for you. 
There are two principal ways to activate your amygdala: the slow 
track or the fast track. The slow track goes through the cortex. This 
means that you can think about things before you become fearful. 
This is both good and bad: good because you can remind yourself 
that there is nothing to fear; bad if you develop irrational fears. 
The fast track to activate your amygdala can trigger your sympa-
thetic nervous system into action and can potentially cause anxiety 
and/or panic. Your amygdala can sound the alarm before your cor-
tex knows what ’ s happening. This means that you can
feel
anxious 
before you even think about something that makes you anxious. 
Within a fraction of a second, the amygdala can use norepinephrine 
to spark electrical impulses throughout your sympathetic nervous 
system to activate your adrenal glands. These glands will dump 
epinephrine (adrenaline) into your bloodstream, which jolts your 
system to increase your breathing, your heart rate, and your blood 
pressure. This is called the fi ght - or - fl ight response. 
A full - blown fi ght - or - fl ight response is very effective in the wild. All 
mammals have this lifesaving capacity. It starts with freezing. When 
you ’ re driving on a country road at night and you see a deer standing in 
the road staring at your rapidly approaching car, the deer is not stupid. 
It ’ s merely doing what animals have done for millions of years to keep 
themselves safe. When they hear the approaching sounds of a poten-
tial predator, they freeze so that they have time to see the predator 
before the predator sees them. Since many predators look for move-
ment, freezing is a good way of instantly becoming invisible. Once the 
animal sees where the predator is located, it can continue with the rest 
of the fi ght - or - fl ight response. The deer is actually preparing for action 
when it freezes. Although it might seem to us that the deer is doing 
nothing, its body is actually bracing to fi ght or to fl ee. 
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Just as with the deer, the rush of adrenaline that you experience pre-
pares your body to get moving by increasing your heart rate and your 
breathing so that you can send more oxygen to your muscles. Adrenaline 
binds to your muscle spindles, intensifying the resting tension 
so that your muscles can burst into action. The blood vessels in your 
skin constrict to limit any potential bleeding if you are wounded, and 
your digestive system shuts down to conserve energy. Saliva stops 
fl owing (so your mouth becomes dry), and the muscles in your bladder 
relax so as not to waste glucose. 
The shorthand sequence goes like this: The amygdala signals the 
hypothalamus, which is responsible for many metabolic processes and 
involved in the autonomic nervous system. This signals the pituitary 
gland, which signals the adrenal glands to release adrenaline and 
later cortisol. This chain is called the
hypothalamus - pituitary - adrenal
(HPA)
axis
. 
Neurochemically, norepinephrine, along with a substance called 
the
corticotropin - releasing factor
(CRF), is sent from the amygdala 
to the hypothalamus, which signals the pituitary gland. The pituitary 
gland then sends a slow message through your bloodstream to your 
adrenal glands, telling them to secrete cortisol, a stress hormone that 
can keep you charged up a little longer than adrenaline does, to deal 
with the stress. On a short - term basis, cortisol facilitates dopamine, 
which keeps you alert and activated. However, cortisol can be corrosive 
to the brain and the body if it stays activated too long. With excessive 
and prolonged cortisol, the levels of dopamine become depleted, and 
this makes you feel awful. 
On a short - term basis, however, cortisol is actually very useful. 
If you encounter stress that requires a prolonged response beyond 
a quick fl ight or a fi ght, your body needs a way to manufacture fuel 
(glucose). Epinephrine (adrenaline) immediately converts glycogen 
and fatty acids, but when the stress is longer-lasting, cortisol takes 
over. It works through the bloodstream, so its effects are slower than 
adrenaline ’ s. 
Cortisol works more systemically than adrenaline does. It triggers 
the liver to make more glucose available in the bloodstream while 
it also blocks insulin receptors in nonessential organs and tissues 
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32 Rew i r e
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so that you get all the glucose (fuel) that you need to deal with the 
threat. Cortisol ’ s work is a long - term strategy of insulin resistance, 
which serves to provide the brain with a sustained level of glucose. 
However, you don ’ t always have a lot of glucose fl oating around, so 
cortisol works to stockpile energy. It converts protein into glyco-
gen and begins to store fat. If the stress is chronic, the increased 
body fat is stored in the abdomen. If you have a growing bulge in 
your midsection, it may be due to cortisol working to store energy. 
Unfortunately, that ’ s not the way you want it to be stored. It ’ s better 
to burn off such stored energy by exercise. 
One of the many problems associated with chronic stress and 
high levels of cortisol is that parts of the brain bear the brunt —
especially the hippocampus. The hippocampus has many cortisol 
receptors; under normal circumstances, this helps to trigger the 
shutting-off of cortisol, much like a thermostat, so that it can turn 
down the production of cortisol. However, when cortisol production 
is excessive and prolonged, the hippocampus receptors themselves 
shut down. The hippocampus then begins to atrophy, and with it 
your memory capacity. 
Unfortunately, the reverse happens for the amygdala. Instead 
of enduring atrophy, it is hypersensitized. The amygdala actually 
becomes more sensitized by an increase in cortisol. From an evolu-
tionary perspective this makes sense, because if our early ancestors 
were stressed by something like dangerous predators, they needed 
to be hyperalert and not think about anything else. 
Because the amygdala can become hypersensitive, chronic stress 
can make you more jumpy and anxious. This is why a war veteran 
with posttraumatic stress disorder (PTSD) will hit the fl oor and 
cover his head when he hears the loud blast of fi reworks. Before he 
has a chance to think about it, the blast reminds him of an impro-
vised explosive device (IED) exploding or a gunshot. His amygdala 
triggers the fi ght - or - fl ight response — a false alarm. 
When you experience severe trauma or excessive chronic stress, the 
once - cooperative partnership between your hippocampus and your 
amygdala becomes skewed in favor of the amygdala. This is because 
the hippocampus is assaulted by excess cortisol and glutamate 
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when the amygdala is pumped up. Cortisol and glutamate act to 
excite the amygdala, and the more it is excited, the more easily it is 
triggered. 
Since your hippocampus provides the context for your mem-
ories, your ability to put stressful events into perspective becomes 
impaired. The amygdala, in contrast, is a generalist. When it gets 
excited, it doesn ’ t care about the context. Any loud noise sets off the 
fi ght - or - fl ight response. 
Just as excessive and prolonged cortisol can be destructive to the 
hippocampus, so can a surplus of the excitatory neurotransmitter 
glutamate. Cortisol initially encourages LTP by increasing gluta-
mate transmission in the hippocampus. This too makes evolution-
ary sense, because when our ancestors were stressed by something, 
such as a particularly dangerous area near a lion ’ s den, they needed 
to remember it. However, in our modern world, this tendency locks 
us into rigid or fi xated patterns. You can ’ t forget what stressed you, 
and more glutamate helps you to remember. 
Too much of a good thing can cause bad things to happen. 
Like excess cortisol, excess glutamate damages the hippocampus 
by allowing electron - snatching calcium ions into cells, which cre-
ates free radicals. If you don ’ t have enough antioxidants in your 
system, free radicals can careen around and punch holes in your cell 
walls, rupturing the cells and potentially killing them. Dendrites, 
the branches of a cell that reach out to other neurons to be poten-
tially receptive to gather information, begin to wither back into the 
cell body. Thoughts and emotions become more rigid and simple. 
Your decisions will be rigid and will probably be destructive instead 
of constructive. 
Fortunately, there are ways to shut down false alarms before they 
become destructive. One way to do it is supported by the pioneer-
ing research of Joseph LeDoux of New York University. LeDoux 
has shown that one area of the amygdala, the central nucleus, is