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Practice builds brain connections
for babies learning language, how to speak
Seattle, WA, July 10: Experience, as the old
saying goes, is the best teacher. And experience seems to play an important
early role in how infants learn to understand and produce language.
Using new technology that measures the magnetic
field generated by the activation of neurons in the brain, researchers tracked
what appears to be a link between the listening and speaking areas of the brain
in newborn, 6-month-old and one-year-old infants, before infants can speak.
The study, which appears in this month's issue of
the journal NeuroReport, shows that Broca's area, located in the front of the
left hemisphere of the brain, is gradually activated during an infant's initial
year of life, according to Toshiaki Imada, lead author of the paper and a
research professor at the University of Washington's Institute for Brain and
Learning Sciences.
Broca's area has long been identified as the seat
of speech production and, more recently, as that of social cognition and is
critical to language and reading, according to Patricia Kuhl, co-author of the
study and co-director of the UW's Institute for Brain and Learning Sciences.
"Magnetoencephalography is perfectly non-invasive
and measures the magnetic field generated by neurons in the brain responding to
sensory information that then 'leaks' through the skull," said Imada, one of the
world's experts in the uses of magnetoencephalography to study the brain.
Kuhl said there is a long history of a link in
the adult brain between the areas responsible for understanding and those
responsible for speaking language. The link allows children to mimic the speech
patterns they hear when they are very young. That's why people from Brooklyn
speak "Brooklynese," she said.
"We think the connection between perception and
production of speech gets formed by experience, and we are trying to determine
when and how babies do it," said Kuhl, who also is a professor of speech and
hearing sciences.
The study involved 43 infants in Finland – 18
newborns, 17 6-month-olds and 8 one-year olds. Special hardware and software
developed for this study allowed the infants' brain activity to be monitored
even if they moved and captured brain activation with millisecond precision.
The babies were exposed to three kinds of sounds
through earphones – pure tones that do not resemble speech like notes played on
a piano, a three-tone harmonic chord that resembles speech and two Finnish
syllables, "pa" and "ta." The researchers collected magnetic data only from the
left hemisphere of the brain among the newborns because they cannot sit up and
the magnetoencephalography cap was too big to securely fit their heads.
At all three ages the infants showed activation
in the temporal part of the brain, Broca's area, that is responsible for
listening and understanding speech, showing they were able to detect sound
changes for all three stimuli. But the pure perception of sound did not activate
the areas of the brain responsible for speaking. However, researchers began
seeing some activation in Broca's area when the 6-month-old infants heard the
syllables or harmonic chords. By the time the infants were one-year old, the
speech stimuli activated Broca's area simultaneously with the auditory areas,
indicating "cross-talk" between the area of the brain that hears language and
the area that produces language, according to Kuhl.
"We think that early in development babies need
to play with sounds, just as they play with their hands. And that helps them map
relationships between sounds with the movements of their mouth and tongue," she
said. "To master a skill, babies have to play and practice just as they later
will in learning how to throw a baseball or ride a bike. Babies form brain
connections by listening to themselves and linking what they hear to what they
did to cause the sounds. Eventually they will use this skill to mimic speakers
in their environments."
This playing with language starts, Kuhl said,
when babies begin cooing around 12 weeks of age and begin babbling around seven
months of age.
"They are cooing and babbling before they know
how to link their mouth and tongue movements. This brain connection between
perception and production requires experience," she said.
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