Through research with mice and humans, scientists have found that brainy activities stimulate new connections between nerve cells and may even help the brain generate new cells, developing neurological "plasticity" and building up a functional reserve that provides a hedge against future cell loss. Any mentally stimulating activity should help to build up your brain. Read, take courses, try "mental gymnastics," such as word puzzles or math problems Experiment with things that require manual dexterity as well as mental effort, such as drawing, painting, and other crafts.
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