Chimpanzee brain anatomical network analysis

In the past year we have published a series of three studies that introduced anatomical network analysis to the brain, specifically in humans (Homo sapiens). Our aim was to highlight pivotal elements and general phenotypic patterns in the morphological organization of the human brain by investigating its intrinsic and extrinsic spatial constraints through topology—that is, patterns of physical interaction. We started with the human brain itself and found that the parahippocampal gyrus of the limbic lobe (i.e., the deep medial foil to the temporal lobe) is of great structural relevance in cerebral architecture. Then we proceeded to investigate community detection as a proxy for modularity in human brain morphology and detected the simultaneous occurrence of two modular patterns which mirror the organization of the surrounding braincase: a vertical division in line with the different ontogenetic processes associated with cranial base and vault, respectively, and a longitudinal gradient consistent with the distinct morphogenetic environments of the three cranial fossae. Lastly, to actually test whether our findings could be contextualized in light of the braincase, as we suspected, we included the skull into the model. Besides matching our expectations in regard to the anatomical system’s modularity, this study suggested that the sphenoid bone and parahippocampal gyrus are the elements of the highest structural relevance, especially due to their role as an interface between soft and hard tissues of the head.

Now we have extended our analysis to a new species, the chimpanzee (Pan troglodytes), and have compared its results to our prior research (Schuurman & Bruner, 2024). Chimpanzees and humans share morphologically complex inferior-medial cerebral regions and a topological organization that corresponds to the spatial arrangement of the braincase. These mutual topological characteristics are interesting because they can probably be traced back 7-10 million years ago, to the Pan–Homo Last Common Ancestor. However, some crucial differences are found between the chimpanzee and human brains as well, namely, in the structural relevance and roles of their respective cerebral components. Most notably, in chimpanzees, the cerebellum is embedded in a more intricate topological context than the parahippocampal gyrus, even compared with humans. The structural relevance of the cerebellum is likely to stem from the lack of expansion and reorganization in the chimpanzee temporal lobes. This could have caused the forebrain to envelop the midbrain and hindbrain more notably than in humans, leading to more spatial interactions between the cerebellum and the other brain regions. We hope this information will help to interpret macroanatomical changes in the brains of fossil hominids.

Tim Schuurman

Automatic hard tissue segmentation

Computed tomography (CT) scanning is a standard way of visualizing hard tissues in living organisms. However, tridimensional reconstruction of CT images requires segmenting the structure at hand, which is time-consuming at best (i.e., manual segmentation) and imprecise at worst (i.e., automatic segmentation), especially in multipart segmentation. To circumvent this issue, Didziokas et al. (2024) have developed an open-access, user-friendly, automated segmentation tool for hard tissues, focusing especially on skull bones: boundary-preserving threshold iteration (BounTI). As its name suggests, BounTI’s operators select the structure of interest based on voxel intensity, which is the only input parameter it needs from the user. This procedure yields good results for bone segmentation, given that osseous tissue usually presents a distinct voxel intensity when compared with its surroundings. An appropriate initial threshold of voxel intensity is one that does not cause separate elements to be joint in the seed (that is, the first recognition of tissue by the algorithm), and which does not cause erroneous separations of single elements (e.g., the parietal bone) in the final stage.

BounTI was tested on skull CT images of various species, including amphibians, reptiles, and mammals. The quality of the assessment’s results demonstrates BounTI’s versatility and effectiveness. However, its performance is bound by the quality of the image; lower resolutions yield worse results. To mend any errors that might arise, BounTI does include options for manual intervention. Lastly, the authors emphasize the tool’s accessibility, human and machine-wise. BounTI can be implemented in a plethora of ways, holding great potential to improve efficiency and accuracy in anatomical studies and clinical applications involving hard tissue segmentation.

Tim Schuurman

A full view of the angular gyrus

The journal Brain Structure and Function has recently published a collection of articles, a special issue, dedicated to the angular gyrus, a fundamental element of the parietal lobe. The Special Issue: Angular Gyrus is guest edited by Kathleen Rockland, research professor in anatomy and neurobiology, as well as William Graves, associate professor of psychology. The angular gyrus (AG) is an interesting area of association cortex because of its diverse structural and functional connectivity, involved in mathematical, spatial and social cognition, among others. Consequently, many approaches have been employed to study its anatomy and functions, although there is still much to be learned about this cortical region and its evolution. The articles featured in the special issue were published over the course of several months, starting in April. They include both original research articles and reviews, and cover a range of different topics including comparative anatomy, connectivity, cytoarchitecture and cognition. All in all, this special issue is meant to be more than the sum of its parts: informing not only about the structure and function of the angular gyrus, but also about brain organization as a whole.

Tim Schuurman