Browsing by Author "Palkki, Varpu"

Objectives. Bilingualism influences brain development, causing both functional and structural changes in the brain. It has been suggested recently that learning and speaking a second language might also cause changes in terms of structural connectivity, i.e., in how distant brain regions are connected to each other via structural white matter tracts. These changes have been found between monolinguals and bilinguals, but it has been unclear how these changes develop as a function of age of acquisition of a second language. Learning two languages simultaneously from birth (early bilinguals) has been proposed to have a different impact on brain development than learning a new language sequentially, for example, at school (late bilinguals). Although structural changes between early and late bilinguals have been studied to some extent, studies on structural connectivity between early and late bilinguals are lacking. Therefore the aim of this thesis was to examine whether early and late bilinguals differ in structural connectivity of the brain. Methods. 15 early bilinguals (Finnish-Swedish) and 15 late bilinguals (Finnish-English) participated in the study. Structural connectivity differences between groups were investigated using diffusion tensor imaging (DTI) based structural connectivity analysis. Four connectivity matrices were used: the density weight, tract volume, number of tracts, and fractional anisotropy. Analysis was performed in both directions (early bilingual > late bilinguals and early bilinguals < late bilinguals) to identify possible brain networks showing a statistically significant between-group difference in structural connectivity. Results and conclusions. A single subnetwork was identified with significantly increased connectivity strength in the early bilingual group compared to the late bilinguals. The network comprised of 4 connections between 5 regions in the right hemisphere. This subnetwork is parallel with the right inferior occipitofrontal fasciculus (IFOF) tract, which has been associated with semantic processing. The results are in line with previous findings and support more bilateral language processing in early bilinguals. Overall the results emphasize the importance of the age of acquisition of a second language.