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| Jörg Rademacher |
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IME, Research Center Jülich, 52425 Jülich
e-mail: j.rademacher@fz-juelich.de |
Poster Presentation: |
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| Human primary sensorimotor cortex revisited. |
| Jörg Rademacher, Stefan Geyer, Karl Zilles | |
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Introduction: The anatomical complexity of the human sensorimotor cortex may confound the results of clinical lesion or functional activation studies. An important problem with classical cytoarchitectonic maps, as well as more recent stereotaxic brain atlases (1), is that they are based on the analysis of one hemisphere. While macroscopic MR-based in vivo brain parcellation methods are well established, testing of their structural-functional relevance makes detailed cytoarchitectonic studies mandatory. To capture more general aspects of regional variability the present investigation implements an extensive sampling of pre- (Areas 4a, 4p, 3a) and postcentral (Areas 3b, 1) cortical areas. Based upon previous results (2), we used a probabilistic and volumetric cytoarchitectonic approach to provide new insights into (i) interhemispheric (a)symmetry, (ii) coordinate-based stereotaxic inaccuracy, (iii) macro-micro covariation and discrepancy, and (iv) the structural basis of sensorimotor integration. Method: 10 adult brains were formalin-fixed, scanned with a 3D-FLASH MR sequence, sectioned, and stained for cell bodies. Areas 4a, 4p, 3a, 3b, and 1 were defined by differences in the laminar densities of neuronal cell bodies (3). After coregistration the topography and variability in the localization of architectonic borders were mapped to a computerized reference brain in Talairach space. Normalized cytoarchitectonic areas from each subject were superimposed to construct probabilistic maps. These maps describe how many brains have a representation of a specific area in a particular voxel. The relationship between sulcal (landmark)-based parcellation units and cytoarchitectonic volumes was analyzed before the normalization procedure. Volumes were visualized as normalized polar plots (volumetric fingerprints) displaying cytoarchitectonic volumes of individual areas across all hemispheres. Results and conclusions: Stereotaxic maps were not mirror-symmetric and there was no consistent volumetric asymmetry indicative of lateralized sensorimotor function. Volumetric maps were used as visual markers (“fingerprints”) for the individual organization of the sensorimotor region. Interindividual variability was larger than interhemispheric variability. Discrepancy maps show that the architectonic variation zones differed from the templates of the Talairach atlas. Adjacent probabilistic maps of pre- and postcentral areas overlap. Complementary use of sulcal landmarks may be essential to differentiate between primary motor vs. primary somatosensory areas. The lack of a consistent covariation between cytoarchitectonically defined areas 4a and 4p, and the macroscopically defined motor hand(knob) region, suggests that macro-microanatomic covariation is exceptional. The same was true for the somatosensory hand(concavity) region and areas 3b and 1. Cytoarchitectonic nomenclature should not be attributed to macroanatomic parcellation systems. Our finding of a volumetric correlation between precentral handknob and postcentral handconcavity regions may relate to sensorimotor integration, since volumetric covariation indicates correlated principles of information processing (3).
References:
- Talairach and Tournoux, 1988. A co-planar stereotaxic atlas of the human brain.
- Geyer S. et al., 1996. Nature, 382:805.
- Passingham, R.E., 2002. Nature Neuroscience, 5:190.
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