Short parietal lobe connections of the human and monkey brain

Abstract

The parietal lobe has a unique place in the human brain. Anatomically, it is at the crossroad between the frontal, occipital, and temporal lobes, thus providing a middle ground for multimodal sensory integration. Functionally, it supports higher cognitive functions that are characteristic of the human species, such as mathematical cognition, semantic and pragmatic aspects of language, and abstract thinking. Despite its importance, a comprehensive comparison of human and simian intraparietal networks is missing. In this study, we used diffusion imaging tractography to reconstruct the major intralobar parietal tracts in twenty-one datasets acquired in vivo from healthy human subjects and eleven ex vivo datasets from five vervet and six macaque monkeys. Three regions of interest (postcentral gyrus, superior parietal lobule and inferior parietal lobule) were used to identify the tracts. Surface projections were reconstructed for both species and results compared to identify similarities or differences in tract anatomy (i.e., trajectories and cortical projections). In addition, post-mortem dissections were performed in a human brain. The largest tract identified in both human and monkey brains is a vertical pathway between the superior and inferior parietal lobules. This tract can be divided into an anterior (supramarginal gyrus) and a posterior (angular gyrus) component in both humans and monkey brains. The second prominent intraparietal tract connects the postcentral gyrus to both supramarginal and angular gyri of the inferior parietal lobule in humans but only to the supramarginal gyrus in the monkey brain. The third tract connects the postcentral gyrus to the anterior region of the superior parietal lobule and is more prominent in monkeys compared to humans. Finally, short U-shaped fibres in the medial and lateral aspects of the parietal lobe were identified in both species. A tract connecting the medial parietal cortex to the lateral inferior parietal cortex was observed in the monkey brain only. Our findings suggest a consistent pattern of intralobar parietal connections between humans and monkeys with some differences for those areas that have cytoarchitectonically distinct features in humans. The overall pattern of intraparietal connectivity supports the special role of the inferior parietal lobule in cognitive functions characteristic of humans.

Differences in Frontal Network Anatomy Across Primate Species

“…Accordingly, in our results, the frontal tracts with the greatest species differences in volume proportion were those connecting with temporal, parietal, and occipital association areas. In the future, the networks of other lobes should be studied more fully to understand differences between human and nonhuman primates (Catani et al, 2017).…”

Modelling white matter with spherical deconvolution: How and why?

“…119 When applied to tractography, this has led to accurate reconstructions of the major human brain pathways and to an improved ability to describe complex white matter anatomy. [112][113][114][115] Finally, it is worth mentioning that the discrete nature of the fibre response matrix, H, makes RL algorithms essentially a dictionary-based spherical deconvolution approach. Here, any type of fibre response (either model based or signal sampled) can be assigned, but more importantly this also allows a straightforward extension to multi-shell data and multi-tissue deconvolution by simply providing the right dictionary of fibre responses and tissue types in a similar fashion as for the multi-tissue version of CSD.…”

Human Paleoneurology and the Evolution of the Parietal Cortex

“…The pattern of connections is distinct, notably at the inferior regions [Catani et al, 2017]. Although fossils have provided scanty evidence of gross morphological differences associated with the inferior parietal lobules, these areas are known to be specialized in humans as well [Bzdok et al, 2016].…”

“…Ralph Holloway [1981] was probably the first to perform an endocranial shape analysis on living and fossil hominoids, evidencing a remarkable parietal variability among different species. In humans, distinctive parietal traits have been known since the first half of the 20th century also in neurobiology [Catani et al, 2017], and advances in the study of the parietal cortex have been stimulating and promising [Mountcastle, 1995]. Nonetheless, the posterior parietal cortex was, until recently, an "uncharted region" [Zilles and PalomeroGallagher, 2001], and parietal lobes have never been taken into consideration when dealing with key changes in human evolution.…”