The cerebral cortex is a likely target for a study of the effects of education on the brain. The cortex ranges from 1.5 to 4.5 millimeters thick, with nerve cells accounting for most of the thickness. The most recently evolved part of the cerebral cortex. Even if an individual lives more than one hundred years, no new nerve cells are formed in this part of the brain. Yet the most rapid growth of the neocortex occurs during the first ten years or so of life.
Dendrites are extensions of the nerve cell membrane that receive the input from other nerve cells.
These branches are very responsive to such input, increasing in number with use and decreasing with disuse. Though most of the research providing information on the plasticity of the brain comes from animal studies, recent experiments from the Brain Research Institute at UCLA have shown similar results in human brains. In Wernicke's area, which deals with word understanding, the nerve cells have more dendrites in college-educated people than in people with only a high school education. Increases in cortical growth as a consequence of stimulating environmental input have been demonstrated at every age, including very old age. Since no two human brains are exactly alike, no one enriched environment will completely satisfy all learners for an extended period.