for my 30th birthday. From Study: Exercise Keeps the Brain Sharp…
Gray matter is home to the neurons that are so important to learning and memory. White matter is sort of the brain’s Internet, with fibers that send signals throughout the brain. Scientists have known for years that these tissues begin to shrink at about the age of 30 in a pattern that closely matches declines in cognitive performances, says Kramer, leader of the research team.

Wait. What was I saying?