According to the NYTimes :
Scientists have suspected for decades that exercise, particularly regular aerobic exercise, can affect the brain. But they could only speculate as to how. Now an expanding body of research shows that exercise can improve the performance of the brain by boosting memory and cognitive processing speed. Exercise can, in fact, create a stronger, faster brain.
This spring, neuroscientists at Columbia University in New York City published a study in which a group of men and women, ranging in age from 21 to 45, began working out for one hour four times a week. After 12 weeks, the test subjects, predictably, became more fit. Their VO2 max, the standard measure of how much oxygen a person takes in while exercising, rose significantly.
But something else happened as a result of all those workouts: blood flowed at a much higher volume to a part of the brain responsible for neurogenesis. Functional M.R.I.’s showed that a portion of each person’s hippocampus received almost twice the blood volume as it did before. Scientists suspect that the blood pumping into that part of the brain was helping to produce fresh neurons.
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The hippocampus plays a large role in how mammals create and process memories; it also plays a role in cognition. If your hippocampus is damaged, you most likely have trouble learning facts and forming new memories. Age plays a factor, too. As you get older, your brain gets smaller, and one of the areas most prone to this shrinkage is the hippocampus. (This can start depressingly early, in your 30’s.) Many neurologists believe that the loss of neurons in the hippocampus may be a primary cause of the cognitive decay associated with aging. A number of studies have shown that people with Alzheimer’s and other forms of dementia tend to have smaller-than-normal hippocampi.
The Columbia study suggests that shrinkage to parts of the hippocampus can be slowed via exercise. The subjects showed significant improvements in memory, as measured by a word-recall test. Those with the biggest increases in VO2 max had the best scores of all.
“It’s reasonable to infer, though we’re not yet certain, that neurogenesis was happening in the people’s hippocampi,” says Scott A. Small, an associate professor of neurology at Columbia and the senior author of the study, “and that working out was driving the neurogenesis.” …
MARIJUANA: We just report the data; we don’t endorse it. A 2005 study on rats found that stimulation of the brain’s receptors for marijuana increased neurogenesis.
ALCOHOL: A 2005 study found that mice that swallowed a moderate amount of ethanol showed more neurogenesis than teetotalers. Other studies on mice have suggested that heavier drinking can be damaging to the brain.CHOCOLATE: In a study published this year, an ingredient in cocoa, epicatechin, was shown to improve spatial memory in mice, especially among those that exercised. Epicatechin can also be found in grapes, blueberries and black tea.