Age-related differences and heritability of the perisylvian language networks

Acquisition of language skills depends on the progressive maturation of specialized brain networks that are usually lateralized in adult population. However, how genetic and environmental factors relate to the age-related differences in lateralization of these language pathways is still not known. We recruited 101 healthy right-handed subjects aged 9–40 years to investigate age-related differences in the anatomy of perisylvian language pathways and 86 adult twins (52 monozygotic and 34 dizygotic) to understand how heritability factors influence language anatomy. Diffusion tractography was used to dissect and extract indirect volume measures from the three segments of the arcuate fasciculus connecting Wernicke’s to Broca’s region (i.e., long segment), Broca’s to Geschwind’s region (i.e., anterior segment), and Wernicke’s to Geschwind’s region (i.e., posterior segment). We found that the long and anterior arcuate segments are lateralized before adolescence and their lateralization remains stable throughout adolescence and early adulthood. Conversely, the posterior segment shows right lateralization in childhood but becomes progressively bilateral during adolescence, driven by a reduction in volume in the right hemisphere. Analysisofthetwinsampleshowedthatgeneticandsharedenvironmentalfactorsinfluencetheanatomyofthosesegmentsthatlateralizeearlier, whereas specific environmental effects drive the variability in the volume of the posterior segment that continues to change in adolescence and adulthood.Ourresults suggest that the age-related differences in the lateralization of thelanguageperisylvianpathwaysare related to the relative contribution of genetic and environmental effects specific to each segment.