For the first time, researchers have used functional magnectic resonance imaging (fMRI) to investigate infantbrain activity in response to speech. They found that, almost from birth, the brain's left hemisphere plays the leading role in processing most language functions. Presented Dec. 2 at the 89th Scientific Assembly and Annual Meeting of the Radiological Society of North America (RSNA), these preliminary findings challenge the previously held belief that left-hemisphere dominance doesn't develop fully until puberty.
"Language lateralization seems to be established almost from birth," said Shantanu Sinha, associate professor of radiology at the David Geffen School of Medicine at UCLA, where the study is ongoing.
Lateralization is the activation of a function, such as speech, from the right or left side of the brain.
"To the best of our knowledge, this is the first time fMRI has been used to study infants," Sinha said. "Using fMRI, we can non-invasively study the neuronal response of newborns to stimulation of different kinds, without any ionizing radiation or pharmaceutical injenctions."
As part of a larger, longitudinal study monitoring the cognitive development of infants with brain injury from birth to age 2, the researchers performed fMRI exams on 42 infants with documented brain injury. The fMRI analysis included cases only where both sides of the brain were equally capable of developing, and excluded children with brain trauma evident on the MR images.
The infants were asleep but not sedated during the procedure. During fMRI, the infants listened through headphones to tapes consisting of scanner noise, nonsense speech and "motherese" speech. The experiments were not sensitive enough to establish whether the infant brains were able to distinguish between the two types of speech. However, definite left-hemisphere-dominant activation patterns appeared during the portions of the tapes containing speech, as opposed to during the portions containing scanner noise.
These early findings challenge the conventional theory that lateralization of language to the left hemisphere is progressive until puberty, starting from an initial state in which neither hemisphere dominates.
"Detailed knowledge about the neural mechanisms associated with increasing levels of speech should prove useful in the study of developmental language disorders, which are the single largest handicapping condition of childhood," Sinha said. "The mapping of specific brain-language relationships should foster understanding of the mental process underlying language itself."
Sinha's co-authors, all from UCLA, included Susan Bookheimer, Meena Garg, Lina Badr and John Grinstead. The National Institutes of Health funded the research.
RSNA is an association of more than 35,000 radiologists, radiation oncologists and related scientists committed to promoting excellence in radiology through education and by fostering research, with the ultimate goal of improving patient care.
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