Dokument

Summary:
The concept of functional asymmetry is a basic principle of organization of human brain function. This basic concept also applies to the encoding of memory data. A number of studies have been conducted to explore the asymmetry of memory encoding using functional magnetic resonance imaging (fMRI), a technique which utilizes the high oxygen levels in activated brain areas to indirectly detect brain activation. The lateralization of encoding processes is determined, among other things, by the verbalizability of the memorized material (Golby, Poldrack et al. 2001; Golby, Poldrack et al. 2002; Powell, Koepp et al. 2005). Encoding of verbal stimuli preferentially relies on left-hemispheric brain regions, while encoding of visual (non-verbal) material relies on right-hemispheric areas. The study of Jansen et al. (Jansen, Sehlmeyer et al. 2009) was used as prototype study for this project, though only containing two stimulus classes and not addressing the issue of reliability. Reliability has only been addressed by a few studies (Bennett and Miller 2010), why we enclosed it into my study. The four objectives of this study are: 1. Implementations of the task at the new 3 tesla Siemens MRI scanner. 2. Expansion of the paradigm by two newly implemented stimulus classes 3. Development of stimuli with less verbalizeable patterns 4. Testing the reliability of the results by comparing it to a second run of the study The establishment of the paradigm at the new scanner was successful. Through the inclusion of two additional stimulus classes (Scenes and Faces), to the existing classes (words and shapes), two additional steps between the existing very well verbalizeable and almost not verbalizeable, were established. The newly introduced almost not verbalizeable patterns showed, as expected, right lateralized activations. Overall similar results to those already published by Golby et al. and Jansen et al could be achieved. The reliability of the results was not entirely homogenous, since the two implemented techniques, the intra-class-correlations (ICC) and the lateralization indices (LI), showed deviating results. LIs resulted in a quite good reliability, but ICCs showed good reliability only for a few select activation clusters. This indicates that in the planning of future fMRI studies, reliability should be a key issue.

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