A Connectomic Hypothesis for the Hominization of the Brain

Abstract

Cognitive abilities of the human brain, including language, have expanded dramatically in the course of our recent evolution from nonhuman primates, despite only minor apparent changes at the gene level. The hypothesis we propose for this paradox relies upon fundamental features of human brain connectivity, which contribute to a characteristic anatomical, functional, and computational neural phenotype, offering a parsimonious framework for connectomic changes taking place upon the human-specific evolution of the genome. Many human connectomic features might be accounted for by substantially increased brain size within the global neural architecture of the primate brain, resulting in a larger number of neurons and areas and the sparsification, increased modularity, and laminar differentiation of cortical connections. The combination of these features with the developmental expansion of upper cortical layers, prolonged postnatal brain development, and multiplied nongenetic interactions with the physical, social, and cultural environment gives rise to categorically human-specific cognitive abilities including the recursivity of language. Thus, a small set of genetic regulatory events affecting quantitative gene expression may plausibly account for the origins of human brain connectivity and cognition.

Rare long-range cortical connections enhance human information processing

“…The brain appears to be unique in terms of its complex architecture spanning multiple scales. 37 Unlike other known physical systems, where the elements communicate with nearest and close neighboring elements (such as, for example, fluids or A B C Figure 4. Using a simple ring structure to demonstrate the improvement in information processing by long-range exceptions is due to the underlying turbulence (A) We created three distinct ring architectures of coupling: nearest neighbor (NN; black ring), EDR (blue ring), and EDR+LR (red ring).…”

Connectional asymmetry of the inferior parietal lobule shapes hemispheric specialization in humans, chimpanzees, and rhesus macaques

“…However, although such regional asymmetries have been identified, additional analyses are needed to address the architecture of neural connectivity ( Ocklenburg et al, 2016 ). A recent ‘connectomic hypothesis for the hominization of the brain’ suggests neural network organization as an intermediate anatomical and functional phenotype between the genome and cognitive capacities, which are extensively modified in the human brain ( Changeux et al, 2020 ). The functions and interactions of brain regions are determined by their anatomical connections ( Passingham et al, 2002 ).…”

Genetic and phylogenetic uncoupling of structure and function in human transmodal cortex

“…There are a number of reasons to suspect that regions where MPC and rsFC diverge the most may support heightened experience-induced development and plasticity 58 . For example, transitions from late childhood to early adulthood are reflected in altered structure-function coupling 26 and these consistent changes in cortical microstructure and myelination patterns are seen in transmodal regions 59 .…”