Biological threat of stress – from the jungle to Wall Street

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  • Wednesday, 09 Mar 2011

IF news about the economy isn’t stressful enough to make you drive your fist through the TV, wait until you hear what stress can do to your brain.

Unrelenting stress can hurt the brain’s leading talent – which is learning – and, in its most potent forms, it can even lead to brain damage.

To underscore how important stress-relieving behaviors are, I am presenting the bad news first. But the bad news is neither the end, nor the most important part, of the story.


You might be surprised to know that the negative linkages between stress and learning were not easy to measure in the laboratory.

First, most of the time stress does not cause brain damage and, oddly enough, certain stressors can actually be quite good for learning.

Second, no one could find a single grouping of physiological states unique to stress. Indeed, it was discovered that a person’s overall responses to aversive stimuli were the same responses they had to their favorite chocolate bar. Or to sex.

Third, no two people react to stress in exactly the same way, which is another way of saying perceptions of stress were (and are) highly subjective.

So how are we going to define “unrelenting stress”?

We actually do have definitions that make sense to a test tube these days, using insights uncovered many years ago and centering around a small but very powerful word: control.

The principle is this: The more out of control you feel over some bad thing coming at you, the more likely you are to experience the type of stress that can hurt you.

“Out of control” is measured in two directions: an inability to control the frequency of the bad stuff coming at you, and an inability to control its severity once the bad stuff has arrived.

This loss of control has been shown to greatly increase the probability of the brain slipping into an anxiety or clinical depression. That can profoundly affect learning, and even cause neurological harm.

The very kinds of experiences in which recessions are marinated, ranging from layoffs to the current slowdown’s favorite flavor – retirement erosion – can provide a perfect elixir for brain debilitation.

Stress response system

Why should a system embedded so deeply in your psyche be so potentially dangerous to you? Stress responses play an extraordinarily important part in our evolutionary survival, after all.

The answer has less to do with biological systems than it has to do with social ones – and also with timing. The brain is well-adapted for solving stress-related problems that are short-term in duration.

The saber-toothed tiger either ate you or you ran away from it, but the whole thing was over in less than five minutes.

Great for a jungle. Lousy for Wall Street. A recession doesn’t last for five minutes. Neither does a bad marriage, or a bad job.

When you try to push a system that was adapted only for solving short-term problems into solving long-term ones, the system first becomes over-extended, then it becomes overwhelmed.

There are many lines of evidence supporting this insight. The metabolic machinery that would actually allow you to handle a stressful experience is almost completely exhausted in 30 minutes (a great deal of it consumed in the first five).

If the system moves beyond this performance benchmark, it starts to deregulate, like a server with too many demands on its time.

Another line of evidence is a reaction to the first: Stress systems possess negative feedback loops that almost immediately ask the brain if it is OK to shut the systems down, even if it just started revving things up.

Why? Because overlong activation hurts things, and your body simply does not have the resources to cope with sustained assaults to its metabolic first responders,

A final line of evidence has to do with the speed of our reactions and our conscious awareness of them. Our stress responses react so quickly that we often do not become aware we are reacting until after we have already started the process. We literally start running away from an aversive stimulus before we are even aware we are moving.

The reason? It simply takes too much time to tell the parts of the brain responsible for consciousness that a big feline is chasing you, time in which you could turn into lunch. So you start running and, in mid-stride, become aware of what you are doing. The delay is about 200 milliseconds.

Milliseconds? That’s less than the time it takes to blink your eyes. The performance envelope of our stress system is designed to solve problems of very short duration.

So what happens when you push a system designed to solve problems lasting less than an hour into an experience where the problems last for months? The answer is depressing.

Severe stress experienced over long periods of time can result in physical brain damage.

Danger zone – long-term stress

When you are stressed, your body gives you two options to respond. One option involves deploying a hormone called epinephrine (or, if you are from Great Britain, adrenalin), supervising the so-called fight-or-flight response. The second choiceinvolves the hormone cortisol.

Which system you deploy first may be in part genetically determined, but the goals of both are the same: to shift enough blood flow to your thighs to get you to move out of the arena of danger – and to give your brain a reason for doing so quickly.

Hormones rage through your body like a storm surge, energy resources are pumped wildly into far-flung tissues, you dump any excess waste your body is currently carrying, and your brain kicks you into a high state of surveillance.

We are going to follow one of the alert signals, the cortisol we just mentioned, to discuss why an over-exposure causes physical damage to specific regions in the brain.

When stress is moderate in severity, acutely experienced, or both, your stress systems work very well. Cortisol is secreted by your adrenal glands, organs that lie atop of your kidneys.

This hormone is part of the Delta Force of your stress response, supervising not only the mission to get you out of danger, but helping to calm you down once the mission is accomplished.

Cortisol even goes into your brain, aiding and abetting regions that are involved in learning (specifically an area of the brain called the hippocampus).

That makes sense; you want to learn quickly from the things that could threaten your biological future.

It is this brain access that provides a conduit for the killing, however. Left to its own devices, dumping cortisol onto unprotected hippocampal cells will kill them just as surely as acid burns skin.

Fortunately, your brain “knows” this and has left the hippocampus with some pretty good protection. Hippocampal cells have within them an heroic protein called Brain Derived Neurotrophic Factor (mercifully shortened to BDNF).

BDNF can protect a nerve cell from the toxic effects of cortisol. As long as the system is not overwhelmed, BDNF does a pretty good job of buffering against the negative effects of stress.

Good news about stress

There are many other issues involved in a complete description of this complex story, including the fact that some people are genetically wired to be more stress-tolerant than others. But the good news is powerful and does not require a genetic explanation.

The brain damage turns out in most cases not to be permanent. You can actually reverse this evil over-regulation in real time, and cure the negative effects listed here.

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