Skip to main content
Login | Suomeksi | På svenska | In English

Browsing by Subject "DTI"

Sort by: Order: Results:

  • Exploring white matter structural anomalies underlying dyslexia : A diffusion tensor imaging study 
    Palo-oja, Peter (2018)
    Developmental dyslexia (DD) affects the accuracy and the fluency of reading without influencing the intelligence of an individual. Problems in phonological awareness (PA), the ability to manipulate the sound structure of words, has been proposed to be the key predictor of DD across languages. Diffusion tensor imaging (DTI) has been used to investigate white matter (WM) structure in DD. The DTI research has concentrated mainly on fractional anisotropy (FA) values, that measure the integrity of WM, and volume of the WM tracts, but also on lateralization differences. Structural alterations have been reported in multiple WM tracts, but left arcuate fasciculus (AF) have most consistently been associated with problems in phonological processing. Also, individuals with DD have been reported to have less prominent leftward lateralization in AF, and inferior fronto-occipital fasciculus (IFOF) compared to non-DD individuals. The participants consisted of 23 individuals with confirmed DD and 21 without DD. In this thesis the reading-related WM tracts were evaluated using deterministic tractography, and the goal was to 1) compare DD and non-DD participants in the FA and volume in reading circuitry, 2) study the associations between reading skills and FA and volume of the WM tracts, and 3) study the lateralization differences in FA and volume. The results of this thesis did not support the current view of the neuroanatomy of DD. Although groups did not differ in FA or in volume of the reading related WM tracts, the groups differed in the lateralization of the WM tracts. Both DD and non-DD participants manifested a rightward lateralization of WM volume in the AF, opposing the earlier findings. Furthermore, DD participants had a unique rightward lateralization of volume in uncinate fasciculus. Subthreshold results in correlations between reading skills and DTI indices also hint toward the heterogeneity found in the DTI research of DD, and do not confirm the role of the AF as the neural correlate of the phonological processing. It seems that no single abnormality in WM structure is responsible of DD. Rather, it seems that DD compiles a vast spectrum of symptoms, with possibly multiple trajectories, and individual compensatory mechanisms in adult samples.
  • Structural connectivity changes in the brain between early and late bilinguals 
    Palkki, Varpu (2017)
    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.

Yhteystiedot

HELSINGIN YLIOPISTO