Abstracts

One major focus of functional MRI in a clinical use is [ndash] beside the application for language-dominance-analysis [ndash] the establishment of paradigms to examine the function of mediotemporal structures. The aim of the present study is to develop a routinely applicable memory-fMRI paradigm within a clinical setting for the lateralization-selective activation of mediotemporal structures., We applied three different paradigms, each with a different type of stimuli: either faces, words or pictures (landscapes and buildings) within a 1.5 T Scanner (Avanto, Siemens, Erlangen: 385 EPI volumes, TR 3000 ms; TE 40 ms; Slice Thickness: 4 mm, 64*64 matrix, FOV: 250 mm; 35 slices). Each paradigm consisted of randomly intermixed blocks of new stimuli, blocks of repeated stimuli and a contrast condition. As contrasts for the verbal condition character strings were used, for the pictures and faces, scrambled images were applied. The subjects were given a task which consisted of a living/nonliving decision in the verbal paradigm, a landscape/building-decision in the picture paradigm and a female/male-decision in the faces paradigm. To examine the lateralization of the mediotemporal activation without possible influences of language-dominance, each of these three paradigms was applied to 19 healthy subjects with typical right-hemispheric language-dominance, determined by an established language-lateralization paradigm. We inspected the following contrasts for each paradigm: new vs. repeated stimuli and new meaningful stimuli vs. contrast condition.
Since the lateralization of an activation is dependent on the statistical threshold that is applied, a mediotemporal lateralization index based on the activation in the right and left hippocampus and parahippocampal gyrus (LI) was calculated over a range of t-values to examine the threshold-effect on lateralization., The verbal paradigm showed a strong left-lateralized mediotemporal activation for the contrast of new vs. repeated words. During the encoding of faces, the lateralization index exhibited strong right-lateralized activation for the new vs. repeated stimuli. The activation in the picture paradigm was bilateral with a maximum in the left hippocampus for the new vs. repeated condition., The present study revealed a strong left-lateralized activation for the encoding of verbal stimuli and a right-lateralized activation for faces while pictures evoked a more bilateral pattern. After the application in healthy subjects, patients with hippocampal sclerosis and other mediotemporal pathologies will have to be examined to evaluate the clinical use during the presurgical evaluation of patients with temporal lobe epilepsy for the prediction of a post-surgical memory decline.,