International Max Planck Research School

I affirm that I have written the dissertation myself and have not used any sources and aids other than those indicated. 21/10/2005 ______________________________________________ SUMMARY Spatial locations of objects can be represented in the brain with respect to different classes of reference frames, either relative to or independent of the subject's position. This fMRI study compared brain activation induced by a condition involving spatial judgements with respect to the body mid-sagittal plane (the egocentric task) with that induced by judgements about the spatial relationship between certain objects (allocentric task). Comparing both conditions to an object discrimination task (control condition) revealed a largely overlapping occipito-parietal network in the right hemisphere. Direct comparisons of the two spatial tasks revealed higher activations for the allocentric spatial task in medial temporal lobe (MTL) structures of the right hemisphere and in frontal areas of the brain, including the anterior cingulate gyrus (ACC) and medial parts of the prefrontal cortex (MPFC). No brain region exhibited a significant higher activation in the egocentric compared to the allocentric task. Results are interpreted according to a transition approach, in that reflexively performed egocentric localisations are re-mapped into an allocentric code of permanent storage. Here we suggest the involvement of the posterior parietal cortex in managing egocentric spatial representations, with some parts being specialised to convey egocentric information to brain areas responsible for the re-mapping. We propose that two densely interconnected structures (MPFC and MTL) could serve this function, initialised by conflict monitoring of the ACC.