Hey there. It’s me, your brain. Thanks for taking me on this walk in the woods, it’s just what I needed. Ah, nature. So lovely. So relaxing.
Wait, wow, what was that noise? Over there, coming from those bushes right next to the path? That huge thing covered in black fur, rearing up on its hind legs and baring its teeth? A bear, you say?
Okay. No problem. Here’s what I’m going to do. First, my hypothalamus is going to alert the sympathetic nervous system, telling your adrenal glands to release adrenaline (aka epinephrine). It’ll give you a massive boost of energy by releasing stored up glucose (sugar) and fatty acids into your bloodstream. You might need that energy to climb a tree! Wait, bears can climb trees. Well, the adrenaline will also increase your breathing, heart rate, and blood pressure. That will fill your brain and muscles with lots of oxygen-rich blood. Feel it? Now we’re talking. Your senses are sharper. You’re focused! You’re even less sensitive to pain (but lets hope it doesn’t come to that).
The stress response has kept people alive in the face of danger for millions of years.
Now were ready for fight or flight! But, uh, fight doesn’t seem like such a good idea, so back away, slowly, no sudden movements. Now that I’ve got your adrenaline flowing, I’m going to tell those adrenal glands to release cortisol. Adrenaline’s rush goes away in a few minutes, but cortisol will keep your blood pressure high, feed you energy, and keep your mind on high-alert for as long as it takes. Hey, the bear turned around. All right, lets use all that energy and run!
Whoo, nice work, we escaped! It’s great to be back in the safety of civilization. What’s next? Oh, you’ve got that speech to make in front of all those people? How stressful! Don’t worry, I’ll keep that cortisol flowing! Boy, it’s lucky we weren’t mauled, that would have totally messed up your big speech. What’s that? You can’t remember your speech? Well, yeah, that cortisol has a way of messing with your long-term memory — sorry about that! Hmm, feeling a little sick? Oh, yeah, well, I kinda had to put your immune system on hold there for a while. I need to shut down all unnecessary functions to deal with these stressful situations. What are you going to do about the audience waiting for your speech? I don’t know, can’t you just fight them? No? What about fleeing, is that a possibility? Oh. Well, maybe all that cortisol wasn’t such a good idea after all. How was I supposed to know? It was so useful when we ran into that bear!”
The stress response is a necessary, healthy part of life that has kept people alive in the face of danger for millions of years. Modern life, however, is filled with stressful situations like exams and deadlines, where a fight-or-flight response can actually hinder your performance. A normal stress response leaves your body within an hour after danger has passed. But these days, many people have chronic stress due to high-pressure jobs, money worries, or troubles at home. This causes an elevated level of cortisol in the body at all times.
Several studies have demonstrated the detrimental effects of long-term stress on our brains. An overflow of cortisol can stop your brain from creating new memories, or from accessing existing ones. That’s why after a stressful situation, people have trouble remembering details, and say things like, “It was all a blur.” It’s also why you forget things under stress like test answers, your car keys, or where the emergency exit is.
Too much cortisol increases your blood pressure, which may lead to a heart attack or stroke. Epidemiologist Susan Everson of the University of Michigan performed an 11-year study of stress on 2,303 men. She says, “We found that exaggerated blood pressure reactions to stress are related to a greater risk of having a stroke.”
Cortisol also makes it difficult to sleep well. That’s a double-whammy on your memory and cognitive abilities, both of which need sleep to function well, and both of which are negatively impacted by cortisol.
Prolonged exposure to cortisol interferes with the production of brain cells in the hippocampus, an important region in our brains for coping with emotions and consolidating new memories. The National Institutes of Neurological Disorders and Stroke found that new neurons keep generating in the hippocampus — except in the presence of high levels of stress hormones. Other studies have shown cortisol actually destroys neurons in the hippocampus, a problem that worsens with age.
Stress may be most harmful to older people, some of whom have lost about 20 percent of the neurons in their hippocampus. The hippocampus normally tells the hypothalamus when to stop producing cortisol. If the function of the hippocampus is impaired, elevated levels of cortisol can continue to be released, damaging the hippocampus further — a dangerous cycle that can lead to mental decline.
The problem isn’t stress itself. Stress can be healthy and useful in many short-term situations. But it is essential that we learn to manage our stress, so that hormones like cortisol don’t remain in our bodies. Stress management techniques, meditation, and other methods of relaxation activate your parasympathetic system, releasing chemicals which bring your brain back into balance. Importantly, while many studies detail the negative effects of stress on our brains, there are many others that demonstrate that stress-related damage can be reversed. Neurogenesis — the production of new neurons — can be stimulated through challenging mental activity and cardiovascular exercise, and exercise also is a great way to relieve stress.