The sense of self is fundamental to human cognition. It allows individuals to integrate information about their bodies, surroundings, and personal experiences into a coherent representation of themselves. While self-related behaviors vary considerably among primates, the extent to which their underlying brain architecture has been preserved or reorganized during evolution is not well understood.

A research team led by Prof. LIU Ning from the Institute of Biophysics of the Chinese Academy of Sciences and their collaborators used a comparative connectomic approach to analyze brain imaging data from 46 humans, 46 chimpanzees, and 43 macaques.

Building on the human self-processing network (SPN) defined by previous meta-analyses of human neuroimaging studies, the researchers constructed a cross-species homologous connectivity space based on 42 major white matter tracts shared by the three species.

This framework allowed the researchers to map the human SPN onto the brains of chimpanzees and macaques, and to compare local microstructural and transcriptional features between humans and macaques, as well as large-scale structural connectivity across the three species.

The study was published in The Journal of Neuroscience on September 7.

The researchers demonstrated that the spatial distributions of T1w/T2w myelin-sensitive contrast within the SPN were highly similar between humans and macaques. The associated gene expression patterns also showed partial cross-species conservation, with the relevant genes being significantly enriched for human-accelerated, brain-related genes.

While local features showed relative conservation, large-scale structural connectivity within the SPN exhibited pronounced interspecies reorganization. Chimpanzees occupied an intermediate position between macaques and humans overall.

Further analysis revealed that this reorganization exhibited distinct patterns across functional levels. The interoceptive-processing subnetwork was more similar between macaques and chimpanzees, while the exteroceptive-processing subnetwork was more similar between chimpanzees and humans. The mental-self-processing subnetwork displayed more pronounced differentiation among the three species.

Meanwhile, the small-worldness of the SPN increased progressively from macaques to chimpanzees to humans. The distribution of network hubs gradually shifted from primarily the insula in macaques to a combination of the insula and the cingulate cortex in chimpanzees to predominantly the cingulate cortex in humans.

These findings reveal an evolutionary pattern in which the local biological features of the primate SPN remain relatively conserved, while its large-scale network architecture undergoes selective reorganization. The findings also demonstrate that different levels of self-processing follow distinct patterns of cross-species reorganization. This provides comparative neuroscience evidence to help understand the evolutionary development of the neural architecture underlying human self-processing.