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Lateralization over development: the neural basis of emotional prosody processing in children ages 4-12
Poster Session C, Saturday, September 13, 11:00 am - 12:30 pm, Field House
Carolyn Gershman1, Elissa Newport1,2, Barbara Landau1,3, Anna Seydell-Greenwald1,2; 1Georgetown University Medical Center, 2MedStar National Rehabilitation Hospital, 3Johns Hopkins University
It has long been understood that core language functions are lateralized to the left hemisphere (LH) in most healthy adults. Other aspects of language, like emotional prosody (EP) - the vocal expression of emotion - are lateralized to the right hemisphere (RH). When adults have a stroke to one hemisphere, they show deficits in the corresponding cognitive function (in core language after LH stroke and in EP after RH stroke) with limited functional recovery. However, there is a growing body of evidence that in infants and young children, similar strokes do not have the same devastating effects on language. Individuals who had a perinatal stroke—a stroke around the time of birth— to the core language areas of the LH can successfully acquire their core language abilities in homotopic areas of the RH. The young brain’s ability to support core language in the RH may be based on the fact that language functions are less lateralized early in life: a cross-sectional fMRI study of children between the ages of 4 and 12 showed considerable activation of the RH during language tasks in young children, and a gradual decline of that activation throughout childhood. This study focuses on the development of lateralization for EP processing. We hypothesized that, as shown previously for core language abilities, EP lateralization develops gradually over time with maturation and experience. Specifically, we expected that EP activation would begin somewhat bilaterally and shift increasingly towards the RH with age. To investigate this, fMRI data were collected from 41 neurologically healthy children ages 4-12. The fMRI task involved listening to English sentences that were spoken with a happy or sad emotion and judging the speaker’s emotion (EP condition) or listening to the same sentences spoken neutrally and judging sentence content (neutral condition). Individual fMRI activation maps were generated by contrasting activation during emotional vs. neutral blocks to isolate activations specific to EP processing. Lateralization was measured using a lateralization index (LI), which compares activation in the LH vs. RH in frontal and temporal language regions. Group-level activation maps revealed fronto-temporal activation in both hemispheres, but stronger on the right, consistent with prior results in adults. Individual LIs in temporal cortex did not show an age effect, but in frontal cortex, lateralization increased significantly with age. Interestingly, language performance—a composite language score including oral syntax comprehension and two aspects of reading-related skills—was a significantly better predictor of degree of lateralization than was age, indicating the contribution of linguistic experience and maturity beyond chronological age. Overall, these findings lend support to the hypothesis that lateralization of EP develops over time with maturation and experience.
Topic Areas: Prosody, Language Development/Acquisition