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At the same time, neuroscientist Michael Merzenich, at the University of California, San Francisco, has shown that intensive training exercises can dramatically improve the ability of monkeys to identify minute differences in rapid-fire bursts of sound and that these improvements are accompanied by striking changes in the firing patterns of neurons in the monkeys' brains.
In 1994, with a $2.3 million grant from the Charles A. Dana Foundation, Tallal and Merzenich pooled their talents to design new therapies for language-impaired children. The researchers, led by William Jenkins of ucsf and Steve Miller of Rutgers, created computer programs that made the hard consonants easier to hear by elongating them, spacing them farther apart and making them louder. Then the researchers devised a series of computer and classroom games that enticed children to listen to the strange, synthetic sounds and gradually differentiate among them.
After a month of training, three hours a day, five days a week, the kids had made striking progress. The researchers believe the exercises--"aerobics for the brain," Tallal calls them--strengthened the connections between the neurons responsible for distinguishing fast-moving sounds. "It's possible," says Merzenich, "that we may actually be able to eliminate language impairment in a great majority of children."
This optimism seems extraordinary in view of the mounting evidence that both dyslexia and oral-language impairment are inherited disorders. In fact, it seems quite probable that a single gene on chromosome 6 may underlie at least some cases of dyslexia and perhaps other language-based learning problems as well. But a genetic susceptibility to dyslexia does not mean that the condition is inevitable or, after it occurs, that it is irreparable.
Merzenich believes something as simple as an inherited susceptibility to middle-ear infections in the first six months of life could explain at least some of the language problems young children experience. Other researchers think the problem is more fundamental. Autopsy work by Harvard neurologist Dr. Albert Galaburda shows that the brains of dyslexic people are dappled with tiny lesions and out-of-place cells, which suggests that the core problem may lie in the machinery that controls prenatal development.
Certainly difficulties in processing fast sounds show up very early. Developmental psychologist April Benasich, one of Tallal's colleagues at Rutgers, has conditioned six-month-old babies to turn their heads whenever they detect a change in a sequence of tones. As long as the tones are spaced well apart, all the babies do well. (Their reward is a toy that lights up or moves.) But when the interval between tones grows shorter, big differences emerge. Some babies cannot detect the changes unless the sounds are presented 300 milliseconds apart. Others do well when they are separated by a mere 40 milliseconds. The babies who do poorly at this test also have difficulty distinguishing between speech sounds like ba and da.