This link is about a study done with rats and their aging brains. But it reminded me of the nuns' study on aging. Dr. David Snowdon wrote a great book called, "Aging with Grace." In it he tells of his work with the School Sisters of Notre Dame. He asked them to donate their brains (after death, of course!) so he could study how Alzheimer's disease affects the brain.
His findings were astounding. While many sisters whose brains showed Alzheimer's plaques had shown symptoms of the disease, about a third didn't. That's right--many of these sisters had damage to their brains from Alzheimer's, even to a significant degree. But while alive they had shown no symptoms of the disease. This finding revolutionized what scientists had previously thought about the brain. Evidently the nuns' brains were able to develop more connections that compensated for the neurons lost to Alzheimer's plaques. So they were able to stave off the disease. Some of them probably would have developed symptoms if they had lived longer, Snowdon thinks. Still, the study broke open how we understand the aging brain.