Convergent and divergent connectivity patterns of the arcuate fasciculus in macaques and humans
🤖 AI Summary
The cross-species anatomical differences in the arcuate fasciculus (AF) between non-human primates (e.g., macaques) and humans—and their implications for language evolution—remain poorly understood. This study integrates multi-scale techniques: single-neuron viral tracing, fluorescence micro-optical sectioning tomography, 11.7T diffusion MRI tractography, and 7.0T MRI spectral embedding analysis to systematically compare AF connectivity patterns in macaques and humans. We find that while the macaque AF originates in temporoparietal cortex and projects to prefrontal regions, the human AF exhibits marked expansion into the middle temporal gyrus and strengthened structural connectivity among frontal, parietal, and temporal areas. Kullback–Leibler divergence quantification confirms fundamental interspecies divergence in connectional organization. These findings support a novel “connectivity-driven” mechanism for language network evolution, providing critical anatomical evidence for understanding human language specialization and the neural circuit basis of language disorders such as aphasia.
Application Category
📝 Abstract
The organization and connectivity of the arcuate fasciculus (AF) in nonhuman primates remain contentious, especially concerning how its anatomy diverges from that of humans. Here, we combined cross-scale single-neuron tracing - using viral-based genetic labeling and fluorescence micro-optical sectioning tomography in macaques (n = 4; age 3 - 11 years) - with whole-brain tractography from 11.7T diffusion MRI. Complemented by spectral embedding analysis of 7.0T MRI in humans, we performed a comparative connectomic analysis of the AF across species. We demonstrate that the macaque AF originates in the temporal-parietal cortex, traverses the auditory cortex and parietal operculum, and projects into prefrontal regions. In contrast, the human AF exhibits greater expansion into the middle temporal gyrus and stronger prefrontal and parietal operculum connectivity - divergences quantified by Kullback-Leibler analysis that likely underpin the evolutionary specialization of human language networks. These interspecies differences - particularly the human AF's broader temporal integration and strengthened frontoparietal linkages - suggest a connectivity-based substrate for the emergence of advanced language processing unique to humans. Furthermore, our findings offer a neuroanatomical framework for understanding AF-related disorders such as aphasia and dyslexia, where aberrant connectivity disrupts language function.
Problem
Research questions and friction points this paper is trying to address.
Compare arcuate fasciculus connectivity in macaques vs humans
Identify evolutionary differences in language network specialization
Link AF connectivity to disorders like aphasia and dyslexia
Innovation
Methods, ideas, or system contributions that make the work stand out.
Cross-scale single-neuron tracing with viral labeling
High-resolution 11.7T diffusion MRI tractography
Comparative spectral embedding analysis at 7.0T
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