The “10 percent use” is obviously a myth, too, when accounting for our brain’s energy consumption. The brain devours a substantial amount of energy—about 20 percent of all energy required by the body—even though the brain only makes up 2 percent of our body’s total weight. This means that it spends more than ten times the energy per kilogram than the rest of the body. From an evolutionary standpoint, such an energy-draining organ wouldn’t have been permitted to grow, were it unnecessary. The cost of a large brain is to consume more food, and with that there is a need to spend more time and energy to seek out this food. If the brain were indeed 90 percent inactive, then the time and energy expended would be a huge misuse of resources.
Compared to other species, it’s clear that such waste would not have survived long on the path of natural selection.
2. RUN AWAY FROM STRESS
Whenever we feel stressed out, it’s a sign that our brain is pumping out stress hormones. If sustained over months and years, those hormones can ruin our health and turn us into nervous wrecks.
DANIEL GOLEMAN
“The stress begins as soon as I open my eyes in the morning. Earlier than that, actually, because it is often stress that wakes me up. It feels like my brain is racing twenty-four-seven. I spend the entire day thinking about what I should do, and in the evening the anxiety continues to grind me, without any real reason for it.
“I live a hectic life. I do enjoy my job as a business attorney, but I wish it weren’t so time-consuming. I have a lot going on outside of work, too. I have two small children, so I have a perpetual guilty conscience because I’m not always on time to pick them up from day care; then there’s everything else that needs to be planned. Sometimes it seems as though life is just a round of logistics. But even though I have a lot to do at home and at work, I know I would have time for it all if I didn’t stress about it so much. The stress stops me, and I feel completely blocked.
“The stress has increased lately—either that or I’m less able to handle it. I have memory lapses, and I have become more and more absent-minded. I forgot my laptop in a restaurant after lunch, and it wasn’t until I got back to the office that I realized I had left it behind. It was sheer luck that I found it still there. This kind of thing has never happened before.
“The other day, I was on the bus and it was packed; suddenly I found it hard to breathe and had such a feeling of anxiety that I almost panicked. I ended up getting off a few stops early and walking the rest of the way. That has never happened before, either.”
I met with this thirty-seven-year-old man in an outpatient psychiatric clinic. He told me how he had been feeling lately. He was a bit apprehensive to begin with and tried to downplay his problems as though he were ashamed, but eventually he became more open. The level of stress he had been experiencing over several years had gotten worse over time. He had trouble sleeping, and he got irritated over the slightest thing. He had been hiding his angst carefully from his surroundings. This man, married with two children, with a good job and a big apartment … what did he have to be unhappy about? All the outward signs of a successful life were there—but still, something was not right.
After almost an hour of talking, I explained to him that he seemed to have been under a great amount of pressure over a prolonged stretch of time, and that his symptoms—deteriorating memory, trouble sleeping, and the panic attack—most likely had their roots in this stress. He could consider antidepressant medication, but he was not interested in taking drugs. He asked if there were other options. I explained to him that talk therapy is usually effective, and that he should also begin an exercise program by taking up running. That sounded odd to him. “Medication and therapy—that’s one thing, but running? How can that help with stress?”
It’s safe to say that he is not alone in going through these problems. According to the American Psychological Association, 72 percent of all adult Americans experience recurring periods of high stress, and 42 percent suffer from insomnia as a result. Just like my thirty-seven-year-old patient, most of them are aware that medication and therapy are two methods of treating intense stress. And just like him, many don’t know that maybe the most efficient treatment is what this book is all about: physical activity. In fact, exercise and training have shown impressive results in treating and preventing stress. I will now explain why this is the case, and how you, too, can go ahead and literally run away from stress and anxiety.
STRESS FULFILLS A FUNCTION
A good way to start coping with stress is to understand what stress is, and what function it fulfills. In your body, you have what is called the HPA-axis. The HPA-axis is located deep inside the brain, in the part called the hypothalamus gland (the H in HPA). When the brain detects something that it perceives as a threat, like someone screaming at you, the hypothalamus sends a signal to the pituitary gland (the P in HPA) in the brain. The pituitary reacts to the signal by sending out a hormone that goes into your bloodstream and over to your adrenal glands (the A in HPA). They, in turn, react by releasing the stress hormone cortisol, which makes the heart beat faster and harder. All this happens extremely fast; it only takes a second or so to go from you registering the shouting person, to the raised cortisol levels in the blood, to your increased heart rate.
Imagine that you’re standing in front of a large group of colleagues, and you’re about to do a presentation on a project that you’ve worked long and hard on. You feel your heart beat faster, and your mouth is dry even though you’ve just had a glass of water. You wonder if anyone notices that your hand is trembling slightly and that the notes you’re holding are shaking a little. What is happening is your HPA-axis has started to rev up, and cortisol levels in your blood are rising. Your body interprets the situation as if it were confronted by danger, despite the fact that your coworkers are hardly a threat to your life. What begins in your body is a powerful set of biological mechanisms that has been maintained over millions of years of evolution. It has now become a matter of fight-or-flight for your body, even though in this case the “fight” means to give a good presentation and not to fend off a physical attack by your colleagues. However, from a purely biological standpoint, there is no doubt about it: your body is preparing itself for battle.
Rising levels of cortisol put both body and brain on high alert. Muscles need more blood when you’re getting ready to fight or run for your life, so your heart beats faster and harder—an increased heart rate. Your brain becomes focused and sensitized to the smallest change. If you hear so much as a cough in your audience, you’ll react to the sound at lightning speed.
So, stress fulfills a function. It makes you sharper and more focused, and while this is generally a good thing, the reaction can become far too intense for some. Instead of becoming more focused, they’ll have trouble thinking clearly. They experience a loss of control and feel terrible distress. For them, the HPA-axis seems to be spinning out of control.
Amygdala—the stress trigger
But let’s backtrack a bit to see where stress actually starts. The “warning” that your colleagues may constitute a danger doesn’t come from the HPA-axis, but from its engine—the amygdala. The amygdala is a part of the brain the size of an almond, situated deep inside the temporal lobe. You have two amygdalae, one for each half of the brain. The amygdala has been preserved through evolution and is a feature of the brain that we share with many mammals. The reason for its continued presence through time is that it is incredibly important for the survival of our species, as well as that of others. And there’s nothing very remarkable about that. If anything increases your chances of survival, it’s having an effective alarm system that is good at signaling a dangerous situation so you can run away. That’s just what the amygdala does.
The amygdala exhibits a singular property in the biological interplay of stress alarm activation. Not only does it trigger the stress function, it can also be triggered by it. Sound complicated? Here’s how it happens: the amygdala signals danger, and this lea
ds to elevated cortisol levels, which in turn activate the amygdala even more. The stress feeds on itself in a vicious circle.
If the amygdala is left to rev up the HPA-axis uncontrollably, sooner or later you will experience a full-fledged panic attack. Aside from being extremely unpleasant, a panic attack is never a good thing because the afflicted person often behaves irrationally. For our ancestors, panic was not compatible with survival when they came face-to-face with a threatening animal out in the savanna. However, what did increase their chances of survival was keeping a cool head and thinking clearly despite imminent danger.
The body has several built-in brake pedals to slow down the stress response, preventing it from going haywire and bringing on a panic attack. One of these is the hippocampus, which, though associated with the memory center, isn’t just central to our ability to create memories; it also works like a brake so we don’t overreact emotionally. The hippocampus can arrest the stress response, functioning like a counterweight to the amygdala’s stress trigger. This happens continuously in your brain, and not just during stressful situations. There’s always a balance between the amygdala and the hippocampus, each one pulling the other in opposite directions. The amygdala puts the pedal to the metal, while the hippocampus stands on the brakes.
The anxiety subsides
Let’s get back to your presentation, which is now over, so you can take a breather. It doesn’t look like your colleagues noticed your nervousness. Nobody even seems to have had an inkling of what felt like a chaotic storm raging inside you.
Your stress response decreases. Your body and brain lower their guard, as there no longer seems to be any threat. The amygdala’s activities settle down, and cortisol levels drop. Your body lays down its weapons and backs off. You feel calmer.
It’s important that cortisol levels fall as soon as the stressful situation blows over. A surge of cortisol is useful in a serious situation—you need that extra energy to fight or take flight—but walking around with elevated cortisol for an extended period is not a good thing. Too much of this stress hormone can in fact be a poison for the brain cells in the hippocampus, since they can die off from exposure to too much cortisol. Over time—we’re talking months and years here—an excess of cortisol is believed to make the hippocampus shrink in size.
Putting it mildly, this is not good news, because it can lead to memory problems. After all, the hippocampus is the brain’s memory center, and many who experience prolonged elevated stress response, like my patient at the beginning of the chapter, experience worsening short-term memory. Some who have suffered from longtime high stress have difficulty finding words, while others forget places. The latter is more likely to occur because the hippocampus is also involved in spatial navigation.
Stress that creates stress
What is perhaps worse than forgetfulness is that a shrinking hippocampus becomes an increasingly weaker brake for the stress response. The hippocampus’ stress brake gets worn down if the amygdala—the stress trigger—works overtime. The stress response begins to take on a life of its own when the hippocampus can no longer restrain the effects of the amygdala. The amygdala—the gas pedal—speeds up while the hippocampus—the brake—shrinks and becomes less able to slow things down. At this point we enter a vicious circle where stress creates more stress. This is exactly what can happen when there are drawn-out, or chronic, periods of stress: it can literally lead to the brain breaking down. When the brains of people suffering from high stress and anxiety were examined, it was found that their hippocampi were in fact a bit smaller than average, probably due to being slowly eroded by cortisol.
A BODY THAT IS PHYSICALLY FIT COPES BETTER WITH STRESS
It is an irrefutably good idea to attempt to curtail the effect of cortisol on the brain if you wish to get a better handle on stress. This is where exercise enters the picture. If you go for a run or a bike ride, or are otherwise active, cortisol levels will increase over the duration of the activity. This is because physical exertion is a type of stress on the body: your muscles need more energy and oxygen to work properly, so your heart will beat faster and harder to increase blood flow. Heart rate and blood pressure rise. The effects of cortisol in this case are not only normal; they’re crucial for you to perform physically. But your body doesn’t require the same stress response after your training session is over, so cortisol levels drop, in fact falling to below where they were before you had started running. If you keep up a regular running schedule, your cortisol will increase less and less during each successive running session and fall more and more every time you’re done.
Now comes the real interesting part: if you continue to exercise regularly, your level of cortisol will increase less and less, even when you are under stress from reasons other than training. Your body’s stress response, whether it be exercise or work-related, will improve as you become more physically fit. In a nutshell, training teaches the body to not overreact to stress.
Usually, the effect is unmistakable. Maybe you’ve noticed, as I have, that you’re less sensitive to stress during times of intense training. You might go through a highly charged, busy workday, but when you think back on it later you’ll notice that you hardly felt any stress. Often this cannot be explained away with a simple “I’m feeling a bit better overall” because you’ve exercised; instead it is the result of having strengthened your body’s tolerance to stress through physical activity.
EXERCISE CALMS THE STRESS RESPONSE
The Montreal Imaging Stress Test (MIST) demonstrates how we react to stress. This is a computer-generated, timed test in which test subjects are asked to perform head math and mark their answers on the monitor. The result, whether right or wrong, is given immediately after each question.
Before the test, participants are informed that the average tester answered 80 to 90 percent of the questions correctly. When the test begins, the computer will only register 20 to 45 percent of the answers as correct, regardless of whether the subjects are right or wrong. During the test, it is revealed that the test subjects are indeed scoring well below average. Naturally, this is extremely aggravating, which is the intent of the exercise. It’s not unusual for participants drop out of the test and leave in frustration.
CORTISOL, THE “DEATH HORMONE”
Cortisol is sometimes referred to as the “death hormone,” since we know that high levels of cortisol in the blood is damaging to the hippocampus, among other things. This moniker is unnecessarily harsh because the sole purpose of cortisol is not to break down the brain and cause damage; it has many important responsibilities. The trouble is that our stress response, starting with cortisol, has not evolved to contend with today’s longer and higher-stress lifestyle.
In the environment from which human beings evolved—the savanna—stress was typically felt in short bursts. In a threatening situation, our ancestors could choose between going on the attack or running away. They didn’t stay put, day after day, in front of an animal that wanted to eat them. In such situations, cortisol was a mobilizing force that gave us the strength to react.
Today, most of us don’t have to worry about getting eaten or killed. However, stress brought on by work deadlines, bills to pay, and house repairs is not short-term, but persistent. When you worry about rising interests and pickup times at day care, the same response is activated as if you were standing in front of a hungry lion, except the reaction to the lion would be more intense. You run away from the lion—or get eaten by it—and the stress is gone. Fretting about your mortgage won’t literally kill you, of course, but it will produce constant high levels of cortisol, which may beat up your brain in the end.
The stress elevates blood pressure and increases the stress hormone cortisol, which is what the exercise is supposed to do. In other words, it’s the stress reaction that is being studied with the MIST test, not how good testers are at mental arithmetic. So why am I telling you about this annoying test? Because it reveals the amazing impact exercise has on stress. Scie
ntists asked a group of healthy subjects to ride a bike for thirty minutes before they took the test while another group performed gentle exercises without raising their heart rate. Afterwards, cortisol levels were lower in the testers who had biked, because they didn’t react with as strong a stress response as the others. The result was the same, whether the participants were physically fit or not. Training calms the stress response, regardless of your physical condition.
It was also noted that the level of activity in the hippocampus (the part of the brain that acts like a brake on the stress response) was higher in the test subjects who had cycled. The entire HPA-axis was more subdued. The fact is that exercise and physical training is truly a gift for the hippocampus. On the whole, it seems like there’s nothing more beneficial for the hippocampus than being active. As you will read in the chapter called Jog your memory, new cells are created in the hippocampus if you train regularly.
Allow your higher cognitive functions to nip anxiety in the bud
So the hippocampus acts like a brake on the stress response, brakes that are reinforced by physical training. But the hippocampus is not the only brake in your brain. The frontal lobe, which sits behind the forehead, can also inhibit the stress response. The frontal lobe, especially its anterior (front) part called the prefrontal cortex, is the seat of your higher cognitive functions. The ability to check/withhold impulses and abstract and analytical thought are situated here. During stress, the frontal lobe plays a central role in protecting you from overreacting emotionally and acting irrationally.
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