A neurology expert says the findings have great potential.

"That sounds like exciting stuff," says Paul Thompson, associate professor of neurology at the University of California/Los Angeles Medical Center in Los Angeles. "Anyone studying disease knows you really need a good model of what's happening in the normal brain. This is an important focus for understanding brain changes in later years."

Using a special type of magnetic resonance imaging (MRI), Bartzokis and his colleagues mapped the amount of white and gray matter in the frontal and temporal lobes of the brains in 70 normal adult males between the ages of 19 and 76. What they found was that white matter, which lets the different parts of the brain communicate with each other, continued to increase well into the 40s. Gray matter, the part of the brain that contains white matter, declined through adulthood.

Until you hit your 50s, "white matter is replacing gray matter," Bartzokis explains, which is why the size of your brain remains stable after childhood. Unfortunately, the aging process begins to eat away at white matter after your 40s.

Likening gray matter to your computer and white matter to its Internet connections, Bartzokis explains that what is really increasing is something called myelin -- the protective sheath that surrounds nerve fibers in your brain.

"What keeps growing is the myelin," he says. "It affects the speed of the signals that travel from neuron to neuron. What's growing is this insulation. It helps your brain communicate more effectively. It literally allows your brain to work in concert; you're not as prone to impulse."

This may lend credence to the concept of wisdom, Bartzokis says, and explain why adults are better able to control their emotions and make more reasoned decisions than young people do.

Thompson notes that studies have shown nerve cells covered in myelin send messages 100 times faster than nerve cells that are not so covered: "It speeds up the connections. We're losing the number of connections -- sort of a pruning away -- but improving the connections that stay."

The findings could explain how something like trauma, schizophrenia or drug addiction can damage the adult brain, Bartzokis says. Many brain diseases are age-related, he adds, and mapping out normal brain growth in adults could help scientists pinpoint the onset of neurological disorders.

The idea that the brain grows for a much longer period of time than many thought could also lead to new and better treatments for brain disease and addictions, he says. For instance, we may now be able to explain why studies have shown an 18-year-old who tries cocaine is much more likely to become an addict than a 30-year-old who does the same. And drugs that could help increase the amount of myelin in our brains might treat conditions like schizophrenia and Alzheimer's disease more effectively. With this tracking method, Bartzokis says, researchers could literally see whether the drugs were working.

There are also new drugs being studied called neurotrophins, which seem to help nerve cells grow and prevent decay. This type of MRI could help measure how well those drugs work, Bartzokis adds.

"It's a new way of looking at this," he says, and it could even give scientists clues that might help them slow or stop the aging process.

What To Do

Read about Thompson's study, in which doctors used MRIs to map brain development in children.

And the National Institutes of Health (NIH) is funding a nationwide study of 500 children at seven pediatric centers that will use MRIs to track normal brain development in children over the course of five years.

Go here for facts on how the brain works.

For more on brain development, read these HealthScoutNews stories.