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Alzheimeŕs disease (AD) represents the most prevalent neurodegenerative disorder that causes cognitive decline in old age. In its early stages, AD is associated with microstructural abnormalities in white matter (WM). In the current study, multiple indices of diffusion tensor imaging (DTI) and brain volumetric measurements were employed to comprehensively investigate the landscape of AD pathology. The sample comprised 58 individuals including cognitively normal subjects (controls), amnestic mild cognitive impairment (MCI) and AD patients. Relative to controls, both MCI and AD subjects showed widespread changes of anisotropic fraction (FA) in the corpus callosum, cingulate and uncinate fasciculus. Mean diffusivity and radial changes were also observed in AD patients in comparison with controls. After controlling for the gray matter atrophy the number of regions of significantly lower FA in AD patients relative to controls was decreased; nonetheless, unique areas of microstructural damage remained, e.g., the corpus callosum and uncinate fasciculus. Despite sample size limitations, the current results suggest that a combination of secondary and primary degeneration occurrs in MCI and AD, although the secondary degeneration appears to have a more critical role during the stages of disease involving dementia.
The present study investigates the effects of trait anxiety on the neural efficiency of working memory component functions (manipulation vs. maintenance) in the absence of threat-related stimuli. For the manipulation of affectively neutral verbal information held in working memory, high- and low-anxious individuals (N = 46) did not differ in their behavioral performance, yet trait anxiety was positively related to the neural effort expended on task processing, as measured by BOLD signal changes in fMRI. Higher levels of anxiety were associated with stronger activation in two regions implicated in the goal-directed control of attention--that is, right dorsolateral prefrontal cortex (DLPFC) and left inferior frontal sulcus--and with stronger deactivation in a region assigned to the brain's default-mode network--that is, rostral-ventral anterior cingulate cortex. Furthermore, anxiety was associated with a stronger functional coupling of right DLPFC with ventrolateral prefrontal cortex. We interpret our findings as reflecting reduced processing efficiency in high-anxious individuals and point out the need to consider measures of functional integration in addition to measures of regional activation strength when investigating individual differences in neural efficiency. With respect to the functions of working memory, we conclude that anxiety specifically impairs the processing efficiency of (control-demanding) manipulation processes (as opposed to mere maintenance). Notably, this study contributes to an accumulating body of evidence showing that anxiety also affects cognitive processing in the absence of threat-related stimuli.
Thema der vorliegenden Dissertation sind Einflussfaktoren und individuelle Unterschiede im akademische Selbstkonzept von Grundschülern. Das erste Kapitel thematisiert die Bestimmung des Selbstkonzepts, gibt einen Überblick über die theoretischen Wurzeln und beleuchtet unterschiedliche Selbstkonzeptmodelle. Das zweite Kapitel geht auf die Selbstkonzeptentwicklung ein und hebt dabei insbesondere das Internal/External-Frame-of-Reference Modell (I/E-Modell; Marsh, 1986) hervor, welches das Zusammenwirken von externalen (sozialen) und internalen (dimensionalen) Vergleichsprozessen bei der Selbsteinschätzung beschreibt. Auf Basis des I/E-Models werden in Studie 1 das akademische Selbstkonzept und die Schulleistung von Schülern der 1. bis 3. Klassenstufe miteinander in Beziehung gesetzt. Im Zentrum steht dabei die Frage, ab welcher Klassenstufe dimensionale Kontrasteffekte auftreten und welchen Einfluss die Lese-, Rechtschreib- und Mathematikleistung auf die korrespondierenden und nicht korrespondierenden Selbstkonzeptfaktoren haben. Es zeigen sich signifikant negative Pfade von der mathematischen Leistung auf das verbale Selbstkonzept und negative Pfade von der Leseleistung auf das mathematische Selbstkonzept ab der 3. Klasse. Ein Kontrasteffekt innerhalb der verbalen Domäne (Lesen und Schreiben) kann hingegen bei keiner der untersuchten Klassenstufen aufgezeigt werden.
Die zweite und dritte empirische Studie fokussieren mögliche Gruppenunterschiede im akademischen Selbstkonzept anhand bestimmter Schülermerkmale. In Studie 2 wird dabei geprüft, ob sich zwischen Jungen und Mädchen mit und ohne Migrationshintergrund Unterschiede im verbalen und mathematischen Selbstkonzept finden lassen. Kinder mit Migrationshintergrund zeigen trotz schlechterer schulischer Leistungen im Lesen und in Mathematik in diesen Bereichen ein höheres Selbstkonzept als Kinder ohne Migrationshintergrund.
Auch findet sich bereits in der ersten Klasse unter Jungen ein optimistischeres mathematisches und unter Mädchen ein optimistischeres verbales Selbstkonzept. Dies spiegelt sich auch in den tatsächlichen Leistungen der Kinder sowie den Lehrereinschätzungen wider. In Studie 3 wird geprüft, ob Kinder mit ADHS-Symptomen ein positiv illusorisches akademisches Selbstkonzept (Positive Illusory Bias, Hoza et al., 2002) haben. Es zeigt sich, dass zwar Kinder mit ADHS-Symptomen im Vergleich zu Kindern ohne ADHS-Symptome ihre Leistungen deutlich stärker überschätzen, allerdings nur, wenn keine Kontrolle des Schulleistungsniveaus erfolgt. Zudem schätzen sich Kinder mit ADHS-Symptomen in dem Leistungsbereich am besten ein, in dem sie auch am besten abschneiden. Der Positive Illusory Bias scheint also nicht spezifisch für die ADHS zu sein.
Previous studies on European robins, Erithacus rubecula, and Australian silvereyes, Zosterops lateralis, had suggested that magnetic compass information is being processed only in the right eye and left brain hemisphere of migratory birds. However, recently it was demonstrated that both garden warblers, Sylvia borin, and European robins have a magnetic compass in both eyes. These results raise the question if the strong lateralization effect observed in earlier experiments might have arisen from artifacts or from differences in experimental conditions rather than reflecting a true all-or-none lateralization of the magnetic compass in European robins. Here we show that (1) European robins having only their left eye open can orient in their seasonally appropriate direction both during autumn and spring, i.e. there are no strong lateralization differences between the outward journey and the way home, that (2) their directional choices are based on the standard inclination compass as they are turned 180° when the inclination is reversed, and that (3) the capability to use the magnetic compass does not depend on monocular learning or intraocular transfer as it is already present in the first tests of the birds with only one eye open.
The neural correlates of developmental dyslexia have been investigated intensively over the last two decades and reliable evidence for a dysfunction of left-hemispheric reading systems in dyslexic readers has been found in functional neuroimaging studies. In addition, structural imaging studies using voxel-based morphometry (VBM) demonstrated grey matter reductions in dyslexics in several brain regions. To objectively assess the consistency of these findings, we performed activation likelihood estimation (ALE) meta-analysis on nine published VBM studies reporting 62 foci of grey matter reduction in dyslexic readers. We found six significant clusters of convergence in bilateral temporo-parietal and left occipito-temporal cortical regions and in the cerebellum bilaterally. To identify possible overlaps between structural and functional deviations in dyslexic readers, we conducted additional ALE meta-analyses of imaging studies reporting functional underactivations (125 foci from 24 studies) or overactivations (95 foci from 11 studies ) in dyslexics. Subsequent conjunction analyses revealed overlaps between the results of the VBM meta-analysis and the meta-analysis of functional underactivations in the fusiform and supramarginal gyri of the left hemisphere. An overlap between VBM results and the meta-analysis of functional overactivations was found in the left cerebellum. The results of our study provide evidence for consistent grey matter variations bilaterally in the dyslexic brain and substantial overlap of these structural variations with functional abnormalities in left hemispheric regions.