01.27.06
New brain cells!
The common theory is that as we age brain cells slowly die off without ever being replaced. More recent research (found on this article at Scientific American: New Neurons Go with the Spinal Fluid) shows that the brain continues to produce new neurons throught life. This neurogenesis (generation of new nerve cells) occurs in a few specific places, such as where the brain and spinal column meet. They they get moved around in the spinal fluid by the cilia lining the walls.
This reminds me of normal bone growth. If I remember correctly, during puberty our bones become fully developed, proceeding from the middle of the bone toward the ends. It is in these final stages that bone growth is limited to this small active region in the bone. While I am short on specifics, I came across this while watching a documentary on a modern medical procedure to increase a person’s height. Over a period of several months, the doctors maintain an small artificial gap in the end of the tibia, a little bit below the knee cap. Of course, in the end the procedure results in a disproportionate limb size. But in China, and probably the rest of the world, height does have its advantages.