>>>Seems new brain cells are formed in adults.<<<
At least that's already documented to be the case in the Hippocampus (where memories are processed before being stored in the brain) and in the olfactory (smell-related) parts of the brain. Interestingly enough, I have read that neural connections store memories...the neurons themselves do not. What that signifies in this context, I do not know.
I DO know though, that some theorize that our own stem cells can hopefully rejuvenate our brains. Meanwhile, brain rejuvenation occurs naturally in rats, just not in most parts of the human brain as far as we know. Perhaps this is because the human brain is so complex and full of elaborate knowledge bases that such rejuvenation could be more disruptive than beneficial. It could be akin to installing a new hard drive into one's computer without formatting it to correspond with the operating system.
Meanwhile, the following article is rather relevant:
http://www.washingtonpost.com/wp-dyn/articles/A25442-2002Oct14.html
Keeping the Brain Young
A growing mass of research points to the importance of mental recreation. Scientists no longer view the brain as a static organ that inevitably declines with age. Quite the opposite. The brain possesses amazing plasticity and can rebuild damaged connections -- all the while expanding its powers.
Education and intellectual activity are correlated with longer life spans and a reduced risk of Alzheimer's disease. People who aggressively use their minds from early childhood through their forties and fifties maintain their memories better as they age.
The famous Nun Study, which analyzed the lives and brains of 678 Catholic nuns, showed that fostering linguistic ability in childhood and stimulating the expression of complex ideas may protect against Alzheimer's disease.
PET scanning studies found that college graduates have higher activity in the posterior cingulate, a key part of the brain involved in memory performance. Gary Small, director of the UCLA Center on Aging, sums it up in his book, "The Memory Bible":
"Mental stimulation, or exerting our brains in various ways intellectually, may tone up our memory performance, protect us from future decline in brain function, and may even lead to new brain cell growth in the future!"
Even rats do better in stimulating environments. In experiments, the rats with toys and treadmills grew new brain cells, had more synapses, ran faster through mazes and generally appeared more intelligent than rats in ordinary laboratory cages.
"Continual, lifelong mental stimulation is healthy for human brains as well," continues Small. "Mentally and physically active people over age 65 have been found to have higher IQ test scores and higher blood flow into the brain compared with those who remain inactive over a four-year period."