| Abstract No.: | B-G2183 |
| Country: | Canada |
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| Title: | CYTOARCHITECTURE OF THE HUMAN VENTROMEDIAL FRONTAL CORTEX |
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| Authors/Affiliations: | 1 Scott Mackey*; 1 Michael Petrides;
1 McGill University, Montreal, QC, Canada.
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| Content: | Objectives: Studies on cortical architecture are motivated by the strong hypothesis that distinct architectonic areas identify important functional boundaries in the cortex. Progress toward a consensus amongst the neuroanatomical community on the location and spatial extent of architectonic areas is facilitated by objective definitions that may be verified or rejected by other investigators. Quantification of the features which compose the objective definitions should assist in the resolution of ongoing disputes. In order to address these issues in the frontal ventromedial cortex, we used the profile sampling method on areal density images of the cortex to obtain measures of laminar variation between architectonic areas.
Materials and Methods: The frontal ventromedial and orbital surfaces of seven human post-mortem brains were blocked and sectioned at either 12 or 40 microns. A one-in-ten series of sections were prepared histologically with a cell body (Nissl) stain. A representative set of 94 histological sections were selected pseudo-randomly for measurement (at least five sections were selected from each of the fourteen hemispheres). The sections were digitally imaged under low magnification (10x) by light microscopy. Image preprocessing included the segregation of cells according to their size into one of two density images per histological section: a granule cell density image and a pyramidal cell density image. The cortical ribbon contained in the density images was sampled from layer II to the white matter along equally spaced transverse lines. The sample along any one transverse represents a profile of the cortical density at that location. Profiles sampled from one architectonic area should share a common set of features that distinguish them from the profiles sampled from adjacent architectonic areas. On the density profiles, we calculated the density of specific cortical layers which had been manually identified on a separate but identical set of images.
Results: In the frontal ventromedial region, we observed, based on visual examination of the full set of specimens, a series of increasingly laminated architectonic areas in expanding rings emanating from the cortical border with the corpus callosum. In the first ring closest to the corpus callosum, the cortex is agranular (absence of layer IV) and the remaining layers are poorly differentiated. In the next ring, the cortex becomes dysgranular and the cortical layers more distinct while the outer ring contains highly granular cortex with maximally differentiated layers and sublayers. The two features of greatest importance in our visual parcellation of the ventromedial region, namely the granule cell density of layer IV and the prominence of pyramidal cell layer V, were significantly different between these architectonic areas in the quantitative data. Two additional areas, one in the posteriormost sub-genual region (area 25) and another at the frontal pole (area 10) were also identified.
Conclusion: Excluding the posterior sub-genual region (area 25) and the frontal pole (area 10), at least three related architectonic areas, which we label areas 24, 32 and 14 medial, may be distinguished visually and quantitatively on the ventromedial surface of the human frontal lobe. |
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