Exploration of material dependent memory lateralization of the hippocampus and adjourning anatomical regions by fMRI
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),...
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|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.