Slide Slam R15
A weak shadow of early life language processing persists in right hemisphere frontal and temporal cortex of the mature brain
Kelly Martin1, Anna Seydell-Greenwald1, William Gaillard1,2,3, Peter Turkeltaub1,2, Elissa Newport1,2; 1Center for Brain Plasticity and Recovery, Georgetown University Medical Center, 2MedStar National Rehabilitation Hospital, 3Children’s National Hospital
The language system is strongly lateralized to the left hemisphere (LH) in the majority of adults. However, language activity is more bilateral in young children. Indeed, when a stroke in infancy irreversibly damages left perisylvian regions, language is acquired successfully in right perisylvian regions, while a similar stroke in adulthood devastates language abilities. How then do right hemisphere (RH) frontal and temporal regions transition from being ‘equipotential’ for language processing early in life to being unavailable for language processing in the mature brain? Prior work has demonstrated a significant reduction in RH language activation in adults, but we cannot discern from these findings—based on measures of activation magnitude—whether there is a change in the spatial organization of language homologues in the RH. In this study, we investigated the activation pattern of RH regions that are homotopic to typical LH language centers during language processing in healthy children and adults. We hypothesized that after the amount of activity is equated in both hemispheres, if the spatial organization of language activity was just as symmetrical in adults as it was in young children, then a “weak shadow” of early life language processing may persist in the adult RH. Children aged 4-13 (n=39) and young adults (n=14) completed an auditory sentence comprehension fMRI task. To equate activity, we applied fixed cutoffs for the number of active voxels (ranked by t-value) that would be included in each hemisphere for every participant. To evaluate homotopicity, we generated left-right flipped versions of each activation map, calculated spatial overlap (Dice Coefficient) between the LH and RH activity in frontal and temporal regions, and tested for mean differences in the spatial overlap values between the age groups. We found no statistical differences between the age groups in homotopic activation overlap for the frontal or temporal regions. In other words, the spatial organization of language activity was just as symmetrical in adults as it was in young children. These results indicate that homotopic regions in the RH may still be available for language processing to some degree in adults. After a LH stroke in adulthood, recovering some or all of the early-life activation in these regions might be relevant to enhancing recovery of language abilities.