Why Zebras Don't Get Ulcers: The Acclaimed Guide to Stress, Stress-Related Diseases, and Coping

by Robert M. Sapolsky

Your brain consumes phenomenal amounts of energy

brain constitutes something like 3 percent of your body weight but needs nearly a quarter of the energy.

some solid slow wave sleep is needed to restock those stores (mostly of a molecule called glycogen, which is also an ...

Others speculate that sleep is for decreasing brain temperature, letting it cool off from all that daytime brainstorm...

another major reason to sleep is to dream. If you skip a night’s sleep, when you finally get to sleep the next night, you have more REM sleep than normal, suggesting th...

What has become clear is that sleep plays a role in cognition. For example, sleep can facilitate problem solving. This is the realm of “sleeping on a problem,” and then suddenly discovering a solution the next morning while you’re cleaning crud out of the corners of your eyes.

Both slow wave and REM sleep also seem to play roles in the formation of new memories, the consolidation of information from the previous day, even information that became less accessible to you while awake over the course of the day.

the pattern of memory disruption caused by sleep deprivation is different from that caused by stress.

Being exposed to lots of new information during the day is associated with more REM sleep that night.

lots of REM sleep during the night predicts better consolidation of emotional information from the day before, while lots of stage 2 sleep predicts better consolidation of a motor task, and a combination of lots of REM and slow wave sleep predicts better retention of perceptual information.

patterns of activation of hippocampal neurons that occur during learning are then repeated when the animal is sleeping.

It’s as if sleep is the time when the brain practices those new memory patterns over and over, cementing them into place.

Take a normally rested subject, stick her in a brain imager, and ask her to solve some “working memory” problems (holding on to some facts and manipulating them—like adding sequences of three-digit numbers). As a result, her frontal cortex lights up metabolically. Now, take someone who is sleep deprived and he’s awful at the working memory task. And what’s going on in his brain? What you might have guessed is that frontal metabolism would be inhibited, too groggy to get activated in response to the task.

We’re not a nocturnal species and if a person works at night or works swing shifts, regardless of how many total hours of sleep she’s getting, it’s going against her biological nature.

night work or shift work increases the risk of cardiovascular disease, gastrointestinal disorders, immune suppression, and fertility problems.

The hormone CRH seems to be most responsible for this effect. As you’ll recall, the hormone not only starts the glucocorticoid cascade by stimulating ACTH release from the pituitary, but it is also the neurotransmitter that activates all sorts of fear, anxiety, and arousal pathways in the brain. Infuse CRH into a sleeping rat’s brain and you suppress sleep—it’s like throwing ice water onto those happily dozing neurons.

Part of this is due to the direct effects of CRH in the brain, but part is probably due to CRH activating the sympathetic nervous system.

many (but not all) studies show that poor sleepers tend to have higher levels of sympathetic arousal or of glucocorticoids in their bloodstream.

When people are stressed presleep, or are infused with glucocorticoids during sleep, you get less of that helpful sleep pattern during slow wave sleep.

if you infuse glucocorticoids into someone while they’re sleeping, you impair the memory consolidation that would normally be occurring during slow wave sleep.

In the study, one group of volunteers was allowed to sleep for as long as they wanted, which turned out to be until around nine in the morning. As would be expected, their stress hormone levels began to rise around eight. How might you interpret that? These folks had enough sleep, happily restored and reenergized, and by about eight in the morning, their brains knew it. Start secreting those stress hormones to prepare to end the sleep. But the second group of volunteers went to sleep at the same time but were told that they would be woken up at six in the morning. And what happened with them? At five in the morning, their stress hormone levels began to rise.

It was about the stressfulness of anticipating being woken up earlier than desirable. Their brains were feeling that anticipatory stress while sleeping, demonstrating that a sleeping brain is still a working brain.

As an example, older individuals are impaired at turning off epinephrine, norepinephrine, or glucocorticoid secretion after a stressor has finished; it takes longer for levels of these substances to return to baseline.

ideally, the hormones of the stress-response should be nice and quiet when nothing bad is happening, secreted in tiny amounts. When a stressful emergency hits, your body needs a huge and fast stress-response. At the end of the stressor, everything should shut off immediately. And these traits are precisely what old organisms typically lack.

The system turns out to be incredibly sensitive to the size of the stressor, demonstrating a linear relationship between, for example, the extent of the drop in blood pressure and the extent of epinephrine secretion, between the degree of hypoglycemia (drop in blood sugar) and glucagon release. The body not only can sense something stressful, but it also is amazingly accurate at measuring just how far and how fast that stressor is throwing the body out of allostatic balance.

outlet for frustration.

Išsikrovimo búdas - outle

humans also deal better with stressors when we have outlets for frustration—punch a wall, take a run, find solace in a hobby. We are even cerebral enough to imagine those outlets and derive some relief: consider the prisoner of war who spends hours imagining a golf game in tremendous detail. I have a friend who passed a prolonged and very stressful illness lying in bed with a mechanical pencil and a notepad, drawing topographic maps of imaginary mountain ranges and taking hikes through them.

A central feature of an outlet being effective is if it distracts from the stressor. But, obviously, more important is that it also be something positive for you—a reminder that there is more to life than whatever is making you crazed and stressed at the time.

The stress-response is about preparing your body for an explosive burst of energy consumption right now; psychological stress is about doing all the same things to your body for no physical reason whatsoever. Exercise finally provides your body for the outlet that it was preparing for.

Put a primate through something unpleasant: it gets a stress-response. Put it through the same stressor while in a room full of other primates and…it depends. If those primates are strangers, the stress-response gets worse. But if they are friends, the stress-response is decreased. Social support networks—it helps to have a shoulder to cry on, a hand to hold, an ear to listen to you, someone to cradle you and to tell you it will be okay.

social support translated into less of a cardiovascular stress-response. Profound and persistent differences in degrees of social support can influence human physiology as well: within the same family, there are significantly higher glucocorticoid levels among stepchildren than among biological children. Or, as another example, among women with metastatic breast cancer, the more social support, the lower the resting cortisol levels.

People who are socially isolated have overly active sympathetic nervous systems. Given the likelihood that this will lead to higher blood pressure and more platelet aggregation in their blood vessels (remember that from chapter 3?), they are more likely to have heart disease—two to five times as likely, as it turns out. And once they have the heart disease, they are more likely to die at a younger age.

Predictability makes stressors less stressful. The rat with the warning gets two pieces of information. It learns when something dreadful is about to happen. The rest of the time, it learns that something dreadful is not about to happen. It can relax. The rat without a warning can always be a half-second away from the next shock. In effect, information that increases predictability tells you that there is bad news, but comforts you that it’s not going to be worse—you are going to get shocked soon, but it’s never going to be sprung on you without warning.

By being given news about the stressor to come, you are also implicitly being comforted by now knowing what stressors are not coming.

familiar, predictable stressor by then, and a smaller stress-response is triggered.

when the dentist says, “Only two more times and then we’re done,” it allows us to relax at the end of the second burst of drilling. But I suggest, although I cannot prove it, that unlike the case for the rat, proper information will also lower our stress-response during the pain.

Endless studies have shown that the link between occupational stress and increased risk of cardiovascular and metabolic diseases is anchored in the killer combination of high demand and low control—you have to work hard, a lot is expected of you, and you have minimal control over the process.

So the variable of control is extremely important; controlling the rewards that you get can be more desirable than getting them for nothing. As an extraordinary example, both pigeons and rats prefer to press a lever in order to obtain food (so long as the task is not too difficult) over having the food delivered freely

Loss of control and lack of predictive information are closely related.

A perception of things worsening Yet another critical psychological variable in the stress-response has been uncovered.

The principle often pops up in the realm of human illness. Recall in chapter 9 the scenario where pain is less stressful, can even be welcome, when it means, for example, that the drugs are working, the tumor is shrinking.

Probably not—there is not enough time to derive any psychological benefits from the information. At the other extreme, how about predictive information long in the future? Would you wish for an omnipotent voice to tell you, “Eleven years and twenty-seven days from now your ice-water bath will last ten full minutes”?

Information either just before or long before the stressor does little good to alleviate the psychological anticipation.

Some types of predictive information can even increase the cumulative anticipatory stressor. For example, if the stressor is truly terrible. Would you be comforted by the omnipotent message: “Tomorrow an unavoidable accident will mangle you...

predictive information can make things worse if the information is vague. As I write this section, we continue to be stressed by the maddening vagueness of predictive information in our post-9/11 world, when we are given warnings that read like horoscopes from hell: “Orange Alert: We don’t know w...

these scenarios tell us that predictability does not always work to protect us from stress.

If you believe you have control over stressors that are, in fact, beyond your control, you may consider it somehow to be your fault that the inevitable occurred.

An inappropriate sense of control in the face of awful events can make us feel terrible.

stress-responses can be modulated or even caused by psychological factors, including loss of outlets for frustration and of social support, a perception of things worsening, and under some circumstances, a loss of control and of predictability.

Why do only some of us get stress-related diseases? Obviously we differ as to the number of stressors that befall us. After all the chapters on physiology, you can guess that we differ in how fast our adrenals make glucocorticoids, how many insulin receptors we have in our fat cells, the thickness of our stomach walls, and so on. But in addition to those physiological differences, we can now add another dimension. We differ in the psychological filters through which we perceive the stressors in our world.