Neural correlates of visuospatial bias in patients with left hemisphere stroke: a causal functional contribution analysis based on game theory.

Stroke patients frequently display spatial neglect, an inability to report, or respond to, relevant stimuli in the contralesional space. Although this syndrome is widely considered to result from the dysfunction of a large-scale attention network, the individual contributions of damaged grey and white matter regions to neglect are still being disputed. Moreover, while the neuroanatomy of neglect in right hemispheric lesions is well studied, the contributions of left hemispheric brain regions to visuospatial processing are less well understood. To address this question, 128 left hemisphere acute stroke patients were investigated with respect to left- and rightward spatial biases measured as severity of deviation in the line bisection test and as Center of Cancellation (CoC) in the Bells Test. Causal functional contributions and interactions of nine predefined grey and white matter regions of interest in visuospatial processing were assessed using Multi-perturbation Shapley value Analysis (MSA). MSA, an inference approach based on game theory, constitutes a robust and exact multivariate mathematical method for inferring functional contributions from multi-lesion patterns. According to the analysis of performance in the Bells test, leftward attentional bias (contralesional deficit) was associated with contributions of the left superior temporal gyrus and rightward attentional bias with contributions of the left inferior parietal lobe, whereas the arcuate fascicle was contributed to both contra- and ipsilesional bias. Leftward and rightward deviations in the line bisection test were related to contributions of the superior longitudinal fascicle and the inferior parietal lobe, correspondingly. Thus, Bells test and line bisection tests, as well as ipsi- and contralesional attentional biases in these tests, have distinct neural correlates. Our findings demonstrate the contribution of different grey and white matter structures to contra- and ipsilesional spatial biases as revealed by left hemisphere stroke. The results provide new insights into the role of the left hemisphere in visuospatial processing.

Tractography of Association Fibers Associated with Language Processing.

INTRODUCTION: Several major association fiber tracts are known to be part of the language processing system. There is evidence that high angular diffusion-based MRI is able to separate these fascicles in a constant way. In this study, we wanted to proof this thesis using a novel whole brain "global tracking" approach and to test for possible lateralization. METHODS: Global tracking was performed in six healthy right-handed volunteers for the arcuate fascicle (AF), the medial longitudinal fascicle (MdLF), the inferior fronto-occipital fascicle (IFOF), and the inferior longitudinal fascicle (ILF). These fiber tracts were characterized quantitatively using the number of streamlines (SL) and the mean fractional anisotropy (FA). RESULTS: We were able to characterize the AF, the MdLF, the IFOF, and the ILF consistently in six healthy volunteers using global tracking. A left-sided dominance (LI > 0.2) for the AF was found in all participants. The MdLF showed a left-sided dominance in four participants (one female, three male). Regarding the FA, no lateralization (LI > 0.2) could be shown in any of the fascicles. CONCLUSION: Using a novel global tracking algorithm we confirmed that the courses of the primary language processing associated fascicles can consistently be differentiated. Additionally we were able to show a streamline-based left-sided lateralization in the AF of all right-handed healthy subjects.

Long-term outcome of difficult-to-treat epilepsy in childhood.

So far little is known about the long-term outcome of difficult-to-treat epilepsy syndromes of childhood. The aim of this study was to evaluate precise long-term data concerning the course of such epilepsies after 20 years. By means of a questionnaire we assessed the current situation of patients who had been treated as in-patients at the Department of Children and Adolescents at our Centre due to their difficult-to-treat epilepsy. Of 287 patients who met the inclusion criteria (diagnosis of difficult-to-treat epilepsy according to the final hospital record and hospitalisation for a therapy-resistant epilepsy), 176 were traced successfully and 81 completed and returned the questionnaire. A significant improvement of seizure frequency was reported by 49.7% and complete remission (with or without AEDs) by 25.9% of the patients. Social integration and work was attained by 21%. Cognitive impairment and treatment with more than 3 antiepileptic drugs proved to be significant negative outcome predictors. Among the patient population addressed in this study a high percentage had neurological impairments and/or cognitive deficiencies. Still, with 25.9% an unexpectedly high proportion of patients reached complete clinical remission after 20 years. Our data indicate that the natural course of difficult-to-treat epilepsies of childhood may be better than previously suggested.