The brain is not too different from the rest of your body. It needs to be well-nourished. All animals except humans know this instinctively; because the head is elevated whenever an animal moves, sleep is the best time to feed an animal's brain the blood they need for brain nourishment. An animal is always in a prone position during sleep, and its head falls lower than the rest of its body.
Unlike animals, we humans sleep with our heads elevated on pillows, making the workload to feed the brain -- its essential blood -- even harder. (We could say this is a true uphill struggle, as the blood must go up and against the ever-present force of gravity to get to the tops of our bodies, the residences of our brains.) If you hold an animal up by its front feet for long enough, the animal will die because its heart and arteries cannot pump enough blood into its brain to keep it alive. Think of what we do to our own brains by insisting that our blood always travel uphill to our brains. It is an unrecognized disease by traditional medicine, but perhaps we all suffer from "brain anemia;" perhaps we're all losing brain cells and brain functioning unnecessarily from having undernourished brains.
Our brains, like the other parts of our bodies, need to be continuously used -- even challenged. If you were to take your right arm and strap it up to your shoulder so you could not use it, the circulation would decrease to that arm. When there is an insufficient blood supply, needed nutrients can't travel to the area: the oxygen supply to these cells would decrease, and the arm would begin to atrophy. If you kept your arm up there long enough, eventually it would die altogether.
The human brain is no different than the animal brain and no different than an unused arm. If we nourish the brain properly, if we use it consistently and correctly, then circulation to it is good, nutrition to the cells is good, oxygenation of those cells is good, and we have a healthy brain. However, an unused brain is the same as an unused arm; when we stop using it, it will atrophy and die.
We see the phenomenon of brain-anemia frequently in individuals who take retirement. You have probably known a person who falls into this category. You knew him as an active, involved person who then went into a sedentary lifestyle. In such people, it is not unusual to see rapid physical and mental deterioration. When the person stopped using their brain, the supply of nutrients and oxygen to the brain dropped, and the brain began to die at an accelerated rate. We also have seen this happen with the death of a loved one. One family I know was a couple well into their late 80s. The wife died suddenly, and at the time of her death, this stately, elderly man, who had been her husband for almost 70 years, was the picture of health. He had a mind that was as sharp as a tack, and a body that could rival much younger men who do frequent and vigorous workouts. He had been in the habit of walking over three hilly miles a day, and doing The New York Times crossword puzzle. Yet, within three months of his wife's death, his mind had deteriorated to the point where he no longer recognized his children. The deterioration was that rapid. A month later, he was dead.
Stress kills brain cells. Mental health professionals are now accepting the strong link between stress and depression: When one is typically present, often the other isn't too far behind. According to the National Institute of Mental Health, the actual neurological damage caused by a combination of the two can be extensive. Developments in brain imaging and neurology have shown how stress works to "rewire" the brain's emotional circuitry, altering its connections in such a way that it affects the way the brain functions.
Stress specifically triggers a "fear center" in the amygdala sector of the brain that takes over emotions and affects thinking. Normally, when a stressful event occurs, our body's response to it fades away. When stress is combined with depression, however, the chemical imbalance in the brain holds onto the stress, keeping the feelings active.
Brain imaging scans have shown, as well, that those who suffer from long-term stress may fail to feel any positive feelings in the prefrontal cortex, the region of the brain that maintains and originates emotions. When that depressed brain is "rewired," dread and fear can flow unimpeded from the amygdala to the prefrontal cortex.
When we're under stress, we can see our memory evaporate almost instantly. Memory and learning are first cousins in the brain. Learning can't happen without a good, intact memory system.
There are many antidotes to stress, and many ways of exercising the brain to keep it healthy and young. As a psychoanalyst, I am partial to the "talking cure" as a method of harmonizing thoughts and feelings, as well as for finding emotional balance. A sense of stress (manifested through either anxiety or depression) is, of course, a mere symptom; once the full range of underlying thoughts and feelings that are creating the symptom are allowed into consciousness -- experienced, observed and understood -- the symptoms are no longer necessary.