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Speech veers left in babies' brains. (Neuroscience).

In adults, the brain's left hemisphere usually assumes primary responsibility for understanding speech. A new brain-imaging study suggests that a fledgling version of this left-brain specialization appears in 2-to-3-month-old babies as they listen to speech, even though they can't utter a word and it's not clear whether they understand any of what they hear.

Language acquisition may reflect the gradual expansion of a network of left-hemisphere regions that enters the neural fray within the first few months of life, propose psychologist Ghislaine Dehaene-Lambertz of the National Center of Scientific Research in Paris and her coworkers. In newborns, however, it remains unknown whether this left-brain network responds only to speech or to any series of rapidly presented sounds, the scientists note in the Dec. 6, 2002 Science.

In the new study, the scientists used a technique called functional magnetic resonance imaging (fMRI) to track neural blood flow in 20 babies as they listened to 20-second presentations of a woman's voice reading a children's book separated by 20-second periods of silence. Some speech segments were played backward.

Left-hemisphere areas roughly corresponding to several adult-brain areas associated with speech comprehension exhibited elevated blood flow--an indirect sign of increased neural activity--as babies listened to regular, but not backward, speech. That finding fits theories that an innate left-hemisphere mechanism underlies language.

The fMRI data also showed that part of the right frontal cortex responded to regular speech with heightened activity. This finding challenges a current theory that the frontal cortex plays no significant role in a baby's thought processes for several months after birth.--B.B.
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Title Annotation:left hemisphere area responsible for understanding speech
Publication:Science News
Article Type:Brief Article
Geographic Code:1USA
Date:Jan 11, 2003
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