Browsing by Subject "DTI"

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  • Rikandi, Eva; Mantyla, Teemu; Lindgren, Maija; Kieseppa, Tuula; Suvisaari, Jaana; Raij, Tuukka T. (2018)
    Background: Functional connectivity is altered in psychotic disorders. Multiple findings concentrate on the default mode network, anchored on the precuneus-posterior cingulate cortex (PC-PCC). However, the nature of the alterations varies between studies and connectivity alterations have not been studied during an ecologically valid natural stimulus. In the present study, we investigated the functional and structural connectivity of a PC-PCC region, where functioning differentiated first-episode psychosis patients from control subjects during free viewing of a movie in our earlier study. Methods: 14 first-episode psychosis patients and 12 control subjects were imaged with GE 3T, and 29 patients and 19 control subjects were imaged with a Siemens Skyra 3T scanner while watching scenes from the movie Alice in Wonderland. Group differences in functional connectivity were analysed for both scanners separately and results were compared to identify any overlap. Diffusion tensor measures of 26 patients and 19 control subjects were compared for the related white matter tracts, identified by deterministic tractography. Results: Functional connectivity was increased in patients across scanners between the midline regions of the PC-PCC and the anterior cingulate cortex-medial prefrontal cortex (ACC-mPFC). We found no group differences in any of the diffusion tensor imaging measures. Conclusions: Already in the early stages of psychosis functional connectivity between the midline structures of the PC-PCC and the ACC-mPFC is consistently increased during naturalistic stimulus. (c) 2018 Elsevier B.V. All rights reserved.
  • Gasbarra, Dario; Pajevic, Sinisa; Basser, Peter J. (2017)
    Tensor-valued and matrix-valued measurements of different physical properties are increasingly available in material sciences and medical imaging applications. The eigenvalues and eigenvectors of such multivariate data provide novel and unique information, but at the cost of requiring a more complex statistical analysis. In this work we derive the distributions of eigenvalues and eigenvectors in the special but important case of m x m symmetric random matrices, D, observed with isotropic matrix-variate Gaussian noise. The properties of these distributions depend strongly on the symmetries of the mean tensor/matrix, (D) over bar. When (D) over bar has repeated eigenvalues, the eigenvalues of D are not asymptotically Gaussian, and repulsion is observed between the eigenvalues corresponding to the same (D) over bar eigenspaces. We apply these results to diffusion tensor imaging (DTI), with m = 3, addressing an important problem of detecting the symmetries of the diffusion tensor, and seeking an experimental design that could potentially yield an isotropic Gaussian distribution. In the 3-dimensional case, when the mean tensor is spherically symmetric and the noise is Gaussian and isotropic, the asymptotic distribution of the first three eigenvalue central moment statistics is simple and can be used to test for isotropy. In order to apply such tests, we use quadrature rules of order t >= 4 with constant weights on the unit sphere to design a DTI-experiment with the property that isotropy of the underlying true tensor implies isotropy of the Fisher information. We also explain the potential implications of the methods using simulated DTI data with a Rician noise model.
  • Palo-oja, Peter (Helsingin yliopisto, 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.
  • Darki, Fahimeh; Massinen, Satu; Salmela, Elina; Matsson, Hans; Peyrard-Janvid, Myriam; Klingberg, Torkel; Kere, Juha (2017)
    The axon guidance receptor, Robo1, controls the pathfinding of callosal axons in mice. To determine whether the orthologous ROBO1 gene is involved in callosal development also in humans, we studied polymorphisms in the ROBO1 gene and variation in the white matter structure in the corpus callosum using both structural magnetic resonance imaging and diffusion tensor magnetic resonance imaging. We found that five polymorphisms in the regulatory region of ROBO1 were associated with white matter density in the posterior part of the corpus callosum pathways. One of the polymorphisms, rs7631357, was also significantly associated with the probability of connections to the parietal cortical regions. Our results demonstrate that human ROBO1 may be involved in the regulation of the structure and connectivity of posterior part of corpus callosum.
  • Taipale, Jaakko (2019)
    This study examines two different approaches in empirical analysis of judges' evaluation of expertise in court: first, an analyst-based approach that employs predefined normative criteria to measure judges' performance, and second, an actor-based approach that emphasizes interpretative flexibility in judges' evaluation practice. I demonstrate how these different approaches to investigating judges' adjudication lead to differing understandings about judges' abilities to evaluate scientific evidence and testimonial. Although the choice of analytical approach might depend on context and purpose in general, I contend that in assessing judges' competence, an actor-based approach that adequately describes the way in which judges relate to and handle expertise is required to properly understand and explain how judges evaluate expertise. The choice of approach is especially important if the resulting understanding of judges' competence is subsequently used as a basis for making normative and prescriptive claims with potential consequences for trial outcomes.
  • Palkki, Varpu (Helsingfors universitet, 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.
  • Sihvonen, Aleksi J.; Virtala, Paula; Thiede, Anja; Laasonen, Marja; Kujala, Teija (2021)
    Current views on the neural network subserving reading and its deficits in dyslexia rely largely on evidence derived from functional neuroimaging studies. However, understanding the structural organization of reading and its aberrations in dyslexia requires a hodological approach, studies of which have not provided consistent findings. Here, we adopted a whole brain hodological approach and investigated relationships between structural white matter connectivity and reading skills and phonological processing in a cross-sectional study of 44 adults using individual local connectome matrix from diffusion MRI data. Moreover, we performed quantitative anisotropy aided differential tractography to uncover structural white matter anomalies in dyslexia (23 dyslexics and 21 matched controls) and their correlation to reading-related skills. The connectometry analyses indicated that reading skills and phonological processing were both associated with corpus callosum (tapetum), forceps major and minor, as well as cerebellum bilaterally. Furthermore, the left dorsal and right thalamic pathways were associated with phonological processing. Differential tractography analyses revealed structural white matter anomalies in dyslexics in the left ventral route and bilaterally in the dorsal route compared to the controls. Connectivity deficits were also observed in the corpus callosum, forceps major, vertical occipital fasciculus and corticostriatal and thalamic pathways. Altered structural connectivity in the observed differential tractography results correlated with poor reading skills and phonological processing. Using a hodological approach, the current study provides novel evidence for the extent of the reading-related connectome and its aberrations in dyslexia. The results conform current functional neuroanatomical models of reading and developmental dyslexia but provide novel network-level and tract-level evidence on structural connectivity anomalies in dyslexia, including the vertical occipital fasciculus.
  • Sihvonen, Aleksi; Ripolles, Pablo; Leo, Vera; Saunavaara, Jani; Parkkola, Riitta; Rodriguez-Fornells, Antoni; Soinila, Seppo; Särkämö, Teppo (2021)
    Listening to vocal music has been recently shown to improve language recovery in stroke survivors. The neuroplasticity mechanisms supporting this effect are, however, still unknown. Using data from a three-arm, single-blind, randomized controlled trial including acute stroke patients (N = 38) and a 3 month follow-up, we set out to compare the neuroplasticity effects of daily listening to self-selected vocal music, instrumental music, and audiobooks on both brain activity and structural connectivity of the language network. Using deterministic tractography, we show that the 3 month intervention induced an enhancement of the microstructural properties of the left frontal aslant tract (FAT) for the vocal music group compared with the audiobook group. Importantly, this increase in the strength of the structural connectivity of the left FAT correlated with improved language skills. Analyses of stimulus-specific activation changes showed that the vocal music group exhibited increased activations in the frontal termination points of the left FAT during vocal music listening compared with the audiobook group from acute to 3 month poststroke stage. The increased activity correlated with the structural neuroplasticity changes in the left FAT. These results suggest that the beneficial effects of vocal music listening on poststroke language recovery are underpinned by structural neuroplasticity changes within the language network and extend our understanding of music-based interventions in stroke rehabilitation.