People are constantly
exposed to stressful situations. These may be physical (like participating in
marathons, being exposed to radiation, and, perhaps surprisingly, exposed to
sedatives or anesthetics). But stress can also be mental, wherein we become
anxious and worried over certain events, existing or anticipated. Whether
physical or mental, stress activates a brain network involving most directly
the hypothalamus, the pituitary gland, and the adrenal cortex to release stress
hormones. Such hormones include several cortisone-like compounds called
glucocorticoids, and the most prominent one in humans is cortisol.
Glucocorticoids have
profound effects on both body and brain. Regulation of glucocorticoids is accomplished
by the brain, and learning experiences have profound effects on this control
system. Most of what was initially known about glucocorticoids was their effect
on the body. I had the great thrill of visiting the pioneer in this field, Hans
Selye, in his laboratory complex at the University of Montreal. He had a whole
room full of medals, awards, and honorary doctorate diplomas. He won
practically every research accolade there was, except the Nobel Prize, one of
several grievous slights by the Nobel committee. Dr. Selye wrote an
autobiography for my book, Discovery
Processes in Modern Biology.
Effects on the Body
Selye’s research led
him to formulate the widely accepted concept of the glucocorticoid system as
accounting for a “General Adaptation Syndrome,” which basically explained how
the brain and body respond to stress. He discovered that glucocorticoids are
“Goldilocks” compounds. That is, a little doesn’t do much, a lot is damaging,
and intermediate levels are “just right.”
A moderate amount of
cortisol is what is normally released every morning before you awaken. By the
way, this is the reason surgeons want to operate early in the morning. This
release helps prepare the body for the day’s activities by mobilizing blood
glucose, typically by breaking down fat and, if needed, protein stores. Glucose
is especially important for the brain, which has huge demands for energy, and
which can only burn glucose for energy. Neurons are energized and memory ability
is enhanced. Another useful thing cortisol does is to reduce the release of
cellular chemicals that cause inflammation.
However, the hormone
also inhibits systems that channel resources for growth and reproduction,
impairs bone formation, and inhibits the immune system. Basically, the idea is
that glucocorticoids help brain and body to respond to temporary emergencies by
assigning lower priority to other physiological needs.
The rub comes when
stress is prolonged. Selye discovered that the beneficial adaptation to
temporary stress cannot be sustained in chronic stress. The system becomes
exhausted and control breaks down.[1]
Under chronic stress, body muscle mass decreases because the system has been
breaking down proteins in order to generate energy. Inflammation bathes cells
in toxic chemicals. Infections increase because the immune system has been
compromised. In obese people, glucocorticoid levels cumulatively increase in
fat cells, increase fat deposits still further, and increase the likelihood of
type 2 diabetes and cardiovascular disease.[2]
Effects on the Brain
In the case of brain,
persistent high levels of glucocorticoid often causes depression. Memory
ability is impaired. Brain degeneration and cognitive decline accelerate. Many
neurons are actually killed. What I want to stress here is that chronic high
levels of cortisone change the neural circuitry that regulates its release. In
other words, the brain learns a new way of functioning if constantly bathed in
high levels of cortisone.
Effects of Learning
Few people make the
connection between glucocorticoid control and learning. The neuronal circuits
that control hormone secretion learn from stressful experience, just as all
neurons learn from whatever they experience. What neurons in the cortisol
control circuit learn in chronic stress is that the usual controls can’t work
any more.
A typical response to
a repeated stress of a certain type (for example, constant quarrels with a
spouse or repeated job failures) can be habituation. It’s like “tuning out.”
Repeated exposure to the same stress teaches the neurons to stop responding as
much as usual. Thus, there is less of the benefits that glucocorticoids provide.
At the same time, the
hormone control system becomes hypersensitive to other stresses, especially
unpredictable or especially severe stresses. The control system learns to
over-react to everything other than the stress to which it has habituated. Now,
the damaging effect of too much glucocorticoid becomes pervasive, both for body
and brain.
Whether the brain
learns stress-coping strategies depends on conscious over-ride of hyper-active responses
to stress, because the neural system (the limbic system) that operates our
emotions also regulates the glucocorticoid control system. We can not only
reduce excessive glucocorticoid but also teach our brain better ways to deal
with stress by doing the following:
·
Simplify
and organize our life,
·
Do one
thing at a time and finish it,
·
Find
pleasure in the little things,
·
Learn to
have a more positive attitude,
·
Laugh and
be happy,
·
Suppress
anxiety,
·
Be more
rational and less emotional,
·
Develop
supportive social relations,
·
Reduce
exposure to stressors.
For more on learning and memory in general, see Dr. Klemm’s new book, Memory Power 101,
Skyhorsepublishing.com.
Photos courtesy of FreeDigitalPhotos.net, by Artur 84 and Ambro
[1] Herman, James P. 2013. Neural control of
chronic stress adaptation. Frontiers in Behavioral Neuroscience. August 8. Doi:
10.3389/fnbeh.2013.00061
[2] Vogelzangs N. et al. 2009. Late-life depression, cortisol, and the metabolic
syndrome. Am J Geriatr Psychiatry. 2009 Aug;17(8):716-21. doi: 10.1097/JGP.0b013e3181aad5d7.
