By LAURAN NEERGAARD The Associated Press 10/16/01 1:31 AM

      WASHINGTON (AP) -- Do genes determine your brain's abilities, or can you retrain the brain to overcome inherited problems, such as helping a learning-impaired child to read?
      Neuroscientist Michael Merzenich has proved that special training, targeting specific brain regions, can help some children with dyslexia and other language-related disabilities to learn. Sophisticated neural imaging shows the retraining, using computerized educational games, leads to physical changes in the brain.
      If it works for dyslexia, Merzenich reasons, why not for more profound neurological disorders like autism or schizophrenia? His theory: Such disorders aren't simply inherited illnesses. Instead, they're inherited brain weaknesses that turn into full-blown disorders only when the ever-changing brain essentially gets stuck in the wrong gear -- and that might be possible to reverse.
      "There's a real prospect of understanding these conditions through understanding the brain as an operational machine that in a sense creates its own capacities," explains Merzenich, of the University of California, San Francisco.
      It sounds provocative. But as Merzenich discussed the latest research at a National Institutes of Health meeting last week, neuroscientists said recent years have brought widespread agreement that the brain's "plasticity" -- continual changes that let us learn new things every day -- sometimes veers out of control, causing developmental disorders once attributed solely to bad genes.
      The challenge now is to understand normal learning well enough to interfere when plasticity goes bad. Merzenich calls it "raising a brain."
      Think of the brain as an incredibly malleable computer. At birth, much of the hardware isn't hooked up and little software is running. But the brain physically changes as it learns, and each change enables new learning and more changes -- constant evolution customized to experience.
      Take vision. Newborns see very little. Day by day, messages beamed from the eyes to a region in the back of the brain literally hook up neural vision circuitry until babies can see normally. But studies of monkeys show patching over one eye makes the brain rewire itself to see only through the eye without the patch.
      "It's a use-it-or-lose-it game during development," says Harvard Medical School's Carla Shatz.
      Change isn't limited to childhood. Other scientists have painstakingly counted how many new brain cells grow in adult rats -- very few if they're kept in plain boring cages but lots if they learn to use exercise wheels. In humans, brain-scanning MRI machines show regions involved in playing music, for example, grow and become more intricately wired as musicians practice.
      But a genetic flaw can knock the whole cycle off kilter. Consider: Some people with dyslexia have problems reading not because of eye problems but because their brains don't properly process sounds, such as the difference between "duh" and "buh," that link to words.
      Merzenich's laboratory created computerized educational games to retrain sound-processing brain regions. The sounds may be drawn out until a child learns to recognize them and then gradually sped up to normal. Put children in MRI machines after about 60 hours of training, and the auditory cortex looks more normal. Tests show the children learn significantly better, too, Merzenich said.
      Merzenich co-founded a California company that now sells the retraining games, called Fast ForWord, to schools and speech therapists.
      More intriguing are severe disorders like autism or schizophrenia. Clearly genes alone don't determine who gets those diseases, because 15 percent of identical twins of autism patients escape the disorder, as do half of identical twins of schizophrenics.
      Merzenich thinks people who inherit a predisposition to those diseases actually get them when brain plasticity runs amok.
      How? He hasn't proved it yet, but his autism theory is that a brain region important for social development, the amygdala, gets bombarded with signals that it can't keep up with, and thus proper development is stymied. It's like a car getting stuck in the mud -- the genetic predisposition -- and revving the engine -- the brain struggling to learn -- just digs it in deeper. Redirect the stalled amygdala and maybe autism can be lessened if not prevented, he says.