Babies' brains charge up to speech sounds.

In the first study of its kind, scientists have charted electrical activity in infants' brains and linked the pulses to a baby's ability to recognize simple syllables. The ebb and flow of cerebral currents suggests that babies discern a change from one syllable to another in less than one-half second, assert psychologists Ghislaine Dehaene-Lambertz and Stanislas Dehaene at the University of Oregon in Eugene.

Separate electrical bursts, which reflect steps taken by the brain to make sense of the sound just heard, appear in infants by age 2 months, the researchers report in the July 28 NATURE.

Prior investigations have found that 2-month-old babies distinguish speech sounds employed in many languages, an ability that dwindles as youngsters learn a native tongue (SN: 2/8/92, p.91).

The Oregon investigators -- who are also affiliated with the National Center for Scientific Research in Paris -- placed a net holding 58 electrodes embedded in wet sponges around the heads of 16 infants, all between 2 and 3 months old. While wearing this gear, youngsters heard a series of four identical syllables (either "ba" or "ga"), followed on some trials by the same syllable and on others by the alternative syllable.

For each child, the researchers calculated overall brain electrical activity across an average of 51 trials.

An initial electrical increase in the brain's temporal lobe peaked about one-fifth of a second after the first presentation of a syllable. Subsequent sounds in a series generated similar, weaker rises in temporal activity The researchers speculate that these peaks reflect processing of basic acoustic information.

A second discharge peaked one-fifth of a second after the first and also declined following the initial syllable presentation. However, that electrical burst returned to its original level when a different syllable concluded a trial, suggesting that the second peak resulted from brain processes devoted specifically to speech sounds, the scientists assert.

Finally about one-half second after a second peak sparked by a new syllable, frontal lobe electrical activity dropped markedly Brain areas that detect unexpected visual and acoustic information probably generated this temporary slump, the psychologists argue.

The first two electrical peaks reached slightly higher levels on the left side of the brain, but the strong left-hemisphere advantage for language typical of most adults did not emerge.