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The human inferior parietal cortex: cytoarchitectonic parcellation and interindividual variability
Svenja Caspers1, Stefan Geyer, Axel Schleicher
1C. and O. Vogt Brain Research Institute, University of Düsseldorf, P.O. Box 10 10 07, 40001 Düsseldorf, Germany.
Insights
This study redefines the human inferior parietal cortex (IPC) cytoarchitecture, identifying seven distinct areas using quantitative methods. This new map offers a more accurate anatomical basis for functional imaging studies.
Area of Science:
- Neuroscience
- Neuroanatomy
- Cognitive Neuroscience
Background:
- The inferior parietal cortex (IPC) is crucial for integrating sensory information and higher cognitive functions.
- Existing cytoarchitectonic maps of the IPC, like Brodmann's two-area model (BA 39 and BA 40), are based on subjective visual inspection and show significant interindividual variability.
- These limitations hinder precise anatomical localization in functional imaging studies.
Purpose of the Study:
- To develop a novel, quantitative, and observer-independent cytoarchitectonic map of the human inferior parietal cortex.
- To identify and delineate distinct cytoarchitectonic areas within the IPC, accounting for topographical variability.
- To provide a more robust anatomical foundation for interpreting functional neuroimaging data.
Main Methods:
- Quantitative analysis of laminar cell density profiles from high-resolution digitized MRI scans of ten postmortem human brains.
- Multivariate statistical methods were employed to define cytoarchitectonic borders objectively.
- The study utilized serial sections stained for cell bodies and 3D registration of the resulting cortical map.
Main Results:
- Identification of seven distinct cytoarchitectonic areas within the IPC, contrasting with the traditional two-area model.
- Five new areas were found in the rostral IPC (region of BA 40), and two in the caudal IPC (region of BA 39).
- Significant interindividual variability in the topography of these areas was observed, with no consistent correlation between macroanatomical landmarks and cytoarchitectonic borders.
Conclusions:
- The human IPC exhibits a more complex cytoarchitectonic organization than previously recognized, comprising seven distinct areas.
- This new, quantitatively defined map reveals microstructural differences suggestive of functional specialization within the IPC.
- The 3D-registered map provides an improved anatomical reference for precise localization and interpretation of functional imaging studies.
Abstract:
The inferior parietal cortex (IPC) integrates information from different sensory modalities and plays an important role in a variety of higher cognitive functions. Brodmann (Brodmann, K., 1909. Vergleichende Lokalisationslehre der Grosshirnrinde. Barth, Leipzig) proposed a cytoarchitectonic subdivision of the IPC into only two cortical areas, a rostral (BA 40) and a caudal (BA 39) area. Although his scheme was repeatedly challenged by other observers, it is still used for the anatomical localization of functional imaging data. The apparent differences between all these cyto- and myeloarchitectonic maps may be caused partly by the observer-dependent procedure of defining cytoarchitectonic borders by pure visual inspection of histological sections and partly by the interindividual variability of cytoarchitecture. The present observations and the resulting cortical map of the IPC are based on quantitative, observer-independent definitions of cytoarchitectonic borders and take into account each area's topographical variability across brains. Ten human postmortem brains were scanned using an MRI 3-D FLASH sequence prior to histological processing. After embedding in paraffin, serial sections through whole brains were prepared, and the sections were stained for cell bodies. Following high-resolution digitization of sections containing the IPC, we defined the cytoarchitecture and borders of each cortical area of this brain region using a multivariate statistical analysis of laminar cell density profiles. In contrast to previous observations, we found seven cytoarchitectonic areas in the IPC: five in the rostral (covering the region of BA 40) and two in the caudal part (covering the region of BA 39). We observed considerable interindividual variability in the topography of each area. A consistent correspondence between macroanatomical landmarks and cytoarchitectonic borders was not found. This new cytoarchitectonic map of the human IPC demonstrates regional differences in the cortical microstructure that is suggestive of functional differentiation. Furthermore, the map is registered in three dimensions and thereby provides a robust anatomical base for interpreting functional imaging studies.
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