There was an interesting article in the New York Times Sunday magazine a couple of weeks ago by Gretchen Reynolds called What Sort of Exercise Can Make You Smarter? Here are some key experpts:
"...exercise changes the structure of the brain and affects thinking."
"...exercise stimulates the creation of new brain cells."
"In an experiment published in the journal of the American College of Sports Medicine, 21 students at the University of Illinois were asked to memorize a string of letters and then pick them out from a list flashed at them. Then they were asked to do one of three things for 30 minutes — sit quietly, run on a treadmill or lift weights — before performing the letter test again. After an additional 30-minute cool down, they were tested once more. On subsequent days, the students returned to try the other two options. The students were noticeably quicker and more accurate on the retest after they ran compared with the other two options, and they continued to perform better when tested after the cool down. “There seems to be something different about aerobic exercise,” Charles Hillman, an associate professor in the department of kinesiology at the University of Illinois and an author of the study, says."
"Why should exercise need to be aerobic to affect the brain? “It appears that various growth factors must be carried from the periphery of the body into the brain to start a molecular cascade there,” creating new neurons and brain connections... For that to happen, “you need a fairly dramatic change in blood flow,” like the one that occurs when you run or cycle or swim."