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Resilience is the buildup of these waste-disposing enzymes, neuroprotective factors, and proteins that prevent the naturally programmed death of cells. I like to think of these elements as armies that remain on duty to take on the next stress. The best way to build them up is by bringing mild stress on yourself: using the brain to learn, restricting calories, exercising, and, as Mattson and your mother would remind you, eating your vegetables.
Excitotoxic stress occurs when there is so much glutamate activity that there isn’t enough ATP to keep up with the energy demand of the increased information flow. If this continues for too long without recovery, there’s a problem. The cell is on a death march—forced to work without food or resources to repair the damage. The dendrites begin to shrink back and eventually cause the cell to die.
Regular aerobic activity calms the body, so that it can handle more stress before the serious response involving heart rate and stress hormones kicks in. It raises the trigger point of the physical reaction. In the brain, the mild stress of exercise fortifies the infrastructure of our nerve cells by activating genes to produce certain proteins that protect the cells against damage and disease. So it also raises our neurons’ stress threshold.
With chronic stress, that stockpile ends up around the midsection, in the form of a spare tire. This is detrimental not only to our physique, but also to our health, because fat stores can easily make their way into the arteries of the heart and cause blockage. For anyone skeptical of the notion that stress can kill, herein lies one of the physical links between stress and heart attacks.
Human studies also show that excess cortisol can block access to existing memories, which explains how people can forget where the fire exit is when there’s actually a fire—the lines are down, so to speak. With too much stress, we lose the ability to form unrelated memories, and we might not be able to retrieve the ones we have.
It also helps explain why constantly high levels of cortisol—due to chronic stress—make it hard to learn new material, and why people who are depressed have trouble learning. It’s not just lack of motivation, it’s because the hippocampal neurons have bolstered their glutamate machinery and shut out less important stimuli. They’re obsessed with the stress.
Cortisol takes over for epinephrine and signals the liver to make more glucose available in the bloodstream, while at the same time blocking insulin receptors at nonessential tissues and organs and shutting down certain intersections so the fuel flows only to areas important to fight-or-flight. The strategy is to make the body insulin-resistant so the brain has enough glucose. Cortisol also begins restocking the shelves, so to speak, replenishing energy stores depleted by the action of epinephrine. It converts protein into glycogen and begins the process of storing fat...If this process continues unabated, as in chronic stress, the action of cortisol amasses a surplus fuel supply around the abdomen in the form of belly fat.
“The mind is so powerful that we can set off the [stress] response just by imagining ourselves in a threatening situation,” writes Rockefeller University neuroscientist Bruce McEwen in his book The End of Stress as We Know It. In other words, we can think ourselves into a frenzy.
This is where the ripple effects of the body’s stress response can lead to full-blown mental disorders such as anxiety and depression, as well as high blood pressure, heart problems, and cancer. Chronic stress can even tear at the architecture of the brain.