http://well.blogs.nytimes.com/2011/11/30/how-exercise-benefits-the-brain/

Perhaps the most inspiring of the recent experiments is one
involving aging human pilots. For the experiment, published last month in the
journal Translational Psychiatry, scientists at Stanford University School of
Medicine asked 144 experienced pilots ages 40 to 65 to operate a cockpit
simulator three separate times over the course of two years.

For all of the pilots, performance declined somewhat as the years passed. A
similar decline with age is common in all of us.

Many people find it more difficult to perform skilled tasks — driving an
automobile, for instance – as they grow older, says Dr. Ahmad Salehi, an
associate professor of psychiatry and behavioral sciences at Stanford and lead
author of the study.

But in this case, the decline was especially striking among one particular group
of men. These aging pilots carried a common genetic variation that is believed
to reduce BDNF activity in their brains. The men with a genetic tendency toward
lower BDNF levels seemed to lose their ability to perform complicated tasks at
almost double the rate of the men without the variation.