Abstract
The orbitofrontal cortex (OFC) is located on the basal surface of the frontal lobe and is distinguished by its unique anatomical and functional features. Clinical and postmortem studies suggest the involvement of the orbitofrontal cortex in psychiatric disorders. However, the exact parcellation of this cortical region is still a matter of debate. Therefore, the goal of this study is to provide a detailed description of the extent of borders of individual orbitofrontal cortical areas using cytoarchitectonic criteria in a large sample of human brains, which could be applied by independent neuroanatomists. To make this microscopic parcellation useful to neuroimaging studies, magnetic resonance images of postmortem brains in the coronal plane were collected prior to the preparation of coronal histological sections from the same brains. A complete series of coronal sections from 6 normal human brains and partial sections from the frontal cortex of 21 normal human brains were stained with general histological and immunohistochemical methods specific for different cell-types. These sections were examined microscopically by two independent neuroanatomists (HBMU and GR) to achieve reproducible delineations. After the borders were determined, the tissue sections were superimposed on the corresponding magnetic resonance images. Based on our cytoarchitectonical criteria, Brodmann's areas 47 and 11 were included in the human orbitofrontal cortex. Area 47 was further subdivided into three medial (located on the medial, anterior and posterior orbital gyri) and two lateral (located on the lateral orbital gyrus) subareas. In addition, we observed an anterior-posterior gradient in the cytoarchitecture of areas 11 and 47. The transverse orbital sulcus corresponds roughly to the transition between the subregions of the anterior and posterior OFC. Finally, the present delineation is contrasted with an overview of the different published nomenclatures for the OFC parcellation.