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Authors & Affiliations
Manuel Dietermann, Sebastian Bludau, Hartmut Mohlberg, Katrin Amunts
Abstract
The fusiform gyrus (FG) in the human brain is essential for higher cortical functions such as recognizing faces and human bodies [1, 2]. Though, the relationship of its structural and functional decompositions in the anterior portion is yet to be better understood [3].
Here, the anterior FG was investigated in ten postmortem brains (five female, five male, including the BigBrain [4]). Using a reproducible, histologically based and software-supported approach, digitized coronal histological brain sections were analyzed [5-7]. A "Grey Level Index" method was used to determine cytoarchitectonic borders between potential new areas [6]. These borders were transferred to the digitized sections to calculate individual 3D maps. The maps were normalized to fit the stereotaxic Colin27 and MNI 152 reference spaces and superimposed to create probability maps, depicting the interindividual variability of the cortical location of the new areas. With hierarchical clustering the cytoarchitectonic characteristics of the new areas were compared to previously described ones [8-10]. Effects for hemisphere and gender were analyzed using a permutation test.
Two areas with distinct cytoarchitectonic features were discovered: FG5 and OTS1. Macroscopically, FG5 covers the anterior FG adjacent to the anterior tip of the midfusiform sulcus. OTS1 is found laterally in the occipitotemporal sulcus. (Fig. 1) Histologically, both areas show a smooth layer transition in all cortical layers. FG5 has prominent cells in layer V and a pronounced layer IIIc. OTS1 appears cell-sparse and less densely packed. Clustering showed close microanatomic relations to nearby FG3 and FG4 [10], in contrast to parahippocampal areas [8], FG1 and FG2 [9], which are adjacent to the occipital lobe. Testing for effect of hemisphere or gender emerged non-significant.
The discovery of FG5 and OTS1 goes beyond previous histological and macroscopical maps that often described the entire FG as a single entity (e.g.[11]). Moreover, while fMRI studies have identified important activations surrounding this region, generating reproducible results for the anterior FG remains to be further investigated due to technical limitations [12]. This study successfully addressed these limitations by identifying two distinct cytoarchitectonic areas, providing a more detailed map of the anterior FG. This advancement refines anatomical understanding and offers a structural basis for further functional investigation.