“In October of 2000 researchers from Duke University made the New York Times with a study showing that exercise is better than sertraline (Zoloft) at treating depression.  What great news!  Unfortunately, it was buried on page fourteen of the Health and Fitness section.  If exercise came in pill form, it would be plastered across the front page, hailed as the blockbuster of the century.”

“In today’s technology-driven, plasma-screened-in world, it’s easy to forget that we are born movers—animals, in fact—because we’ve engineered movement right out of our lives.  Ironically, the human capacity to dream and plan and create the very society that shields us from our biological imperative to move is rooted in the areas of the brain that govern movement.  As we adapted to an ever-changing environment over the past half million years, our thinking brain evolved from the need to hone motor skills.  We envision our hunter-gatherer ancestors as brutes who relied primarily on physical prowess, but to survive over the long haul they had to use their smarts to find and store food.  The relationship between food, physical activity, and learning is hardwired into the brain’s circuitry.

But we no longer hunt and gather, and that’s a problem.  The sedentary character of modern life is a disruption of our nature, and it poses one of the biggest threats to our continued survival.  Evidence of this is everywhere: 65 percent of our nation’s adults are overweight or obese, and 10 percent of the population has type 2 diabetes, a preventable and ruinous disease that stems from inactivity and poor nutrition…”

Source: “SPARK -  The Revolutionary New Science of Exercise and the Brain” by John J. Ratey

“Neurochemically, norepinephrine, along with a substance called the corticotropin-releasing factor (CRF), is sent from the amygdala to the hypothalamus, which signals the pituitary gland.  The pituitary gland then sends a slow message through your bloodstream to your adrenal glands, telling them to secrete cortisol, a stress hormone that can keep you charged up a little longer than adrenaline does, to deal with the stress.  On a short-term basis, cortisol facilitates dopamine, which keeps you alert and activated.  However, cortisol can be corrosive to the brain and the body if it stays activated too long.  With excessive and prolonged cortisol, the levels of dopamine become depleted, and this makes you feel awful.

“On a short-term basis, however, cortisol is actually very useful.  If you encounter stress that requires a prolonged response beyond a quick flight or a fight, your body needs a way to manufacture fuel (glucose).  Epinephrine (adrenaline) immediately converts glycogen and fatty acids, but when the stress is longer-lasting, cortisol takes over.  It works through the bloodstream, so its effects are slower than adrenaline’s.

“Cortisol works more systemically than adrenaline does.  It triggers the liver to make more glucose available in the bloodstream while it also blocks insulin receptors in nonessential organs and tissues so that you get all the glucose (fuel) that you need to deal with the threat.  Cortisol’s work is a long-term strategy of insulin resistance, which serves to provide the brain with a sustained level of glucose.  However, you don’t always have a lot of glucose floating around, so cortisol works to stockpile energy.  It converts protein into glycogen and begins to store fat.  If the stress is chronic, the increased body fat is stored in the abdomen.  If you have a growing bulge in your midsection, it may be due to cortisol working to store energy.  Unfortunately, that’s not the way you want it to be stored.  It’s better to burn off such stored energy by exercise.

“One of the many problems associated with chronic stress and high levels of cortisol is that parts of the brain bear the brunt—especially the hippocampus.  The hippocampus has many cortisol receptors; under normal circumstances, this helps to trigger the shutting-off of cortisol, much like a thermostat, so that it can turn down the production of cortisol.  However, when cortisol production is excessive and prolonged, the hippocampus receptors themselves shut down.  The hippocampus then begins to atrophy, and with it your memory capacity.”

Source: Rewire Your Brain by John B. Arden