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Spark
by John J. Ratey, Eric Hagerman

They don’t know that toxic levels of stress erode the connections between the billions of nerve cells in the brain or that chronic depression shrinks certain areas of the brain. And they don’t know that, conversely, exercise unleashes a cascade of neurochemicals and growth factors that can reverse this process, physically bolstering the brain’s infrastructure. In fact, the brain responds like muscles do, growing with use, withering with inactivity. The neurons in the brain connect to one another through “leaves” on treelike branches, and exercise causes those branches to grow and bloom with new buds, thus enhancing brain function at a fundamental level.

I didn't consider incorporating exercise into my routine until I read this book.

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  • “…conversely, exercise unleashes a cascade of neurochemicals and growth factors that can reverse this process, physically bolstering the brain’s infrastructure. In fact, the brain responds like muscles do, growing with use, withering with inactivity. The neurons in the brain connect to one another through “leaves” on treelike branches, and exercise causes those branches to grow and bloom with new buds, thus enhancing brain function at a fundamental level.”

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  • the point of exercise is to build and condition the brain.

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  • It turns out that moving our muscles produces proteins that travel through the bloodstream and into the brain, where they play pivotal roles in the mechanisms of our highest thought processes.

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  • experiments with lab rats suggest that forced exercise doesn’t do the trick quite like voluntary exercise.

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  • environmental deprivation could shrink the brain…In examining cats raised with one eye sewn shut, they found that the visual cortex was significantly smaller.

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  • Exercise spawns neurons, and the stimulation of environmental enrichment helps those cells survive.

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  • cognitive flexibility improves after just one thirty-five-minute treadmill session at either 60 percent or 70 percent of maximum heart rate.

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  • 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.

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  • “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.

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  • 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.

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  • 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.

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  • 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.

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  • This is depressing, I thought I was doing so well with 30 minutes a day.

    The kicker is that even if we followed the most demanding governmental recommendations for exercise and logged thirty minutes of physical activity a day, we’d still be at less than half the energy expenditure for which our genes are encoded. Paleolithic man had to walk five to ten miles on an average day, just to be able to eat.

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  • 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.

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  • 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.

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  • 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.

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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.

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  • genetic lottery sucks

    There are a number of scenarios in which the body fails to shut off the flow of stress hormones. The most obvious is simply unrelenting stress. If we never get a break, the recovery process never gets started, the amygdala keeps firing, and the production of cortisol spills over healthy levels. Sometimes the fight-or-flight switch gets stuck in the on position. It can be a function of genetics, according to epidemiological surveys: if you put a random group of people in a stressful public speaking situation, those whose parents suffered from hypertension still show elevated levels of cortisol twenty-four hours after the speech.

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  • The scientific name for the disorder speaks volumes: hypercortisolism. Its symptoms are eerily similar to those of chronic stress: weight gain around the midsection; breaking down muscle tissue to produce unnecessary glucose and then fat; insulin resistance and possibly diabetes; panic attacks, anxiety, depression, and increased risk of heart disease. One of the many correlations Starkman has shown is that the extent of hippocampal shrinkage and memory loss is directly proportional to elevations in cortisol.

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  • While chronic stress is bullying the hippocampus—pruning its dendrites, killing its neurons, and preventing neurogenesis—the amygdala is having a field day. The stress overload creates more connections in the amygdala, which keeps firing and calling for cortisol, even though there’s plenty of the hormone available, and the negative situation feeds on itself. The more the amygdala fires, the stronger it gets. Eventually the amygdala takes control of its partnership with the hippocampus, repressing the context—and thus the connection to reality—and branding the memory with fear. The stress becomes generalized, and the feeling becomes a free-floating sense of fear that morphs into anxiety. It’s as if everything is a stressor, and this colors perception and leads to even more stress.

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