How does the brain fold, and what does it fold into? Searching for a new morphological syntax for the cerebral cortex*

The mammalian cerebral cortex is a morphologically complex structure spanning a wide range of sizes and shapes across species. We have previously demonstrated that the cortical folding across various mammalian species follows a universal scaling law that can be derived from a simple statistical physics model [1]. The same law also applies across healthy humans [2] and cortical regions [3]. Here, we show that, despite all this diversity, cortical shape can be universally and explicitly expressed as the hierarchical composition of folded structures of different sizes.

More specifically, using a new set of theory-inspired morphological variables [4] that capture shape and size of the cortex as functions of length scale, we show [5] that for 11 different primate species, there is a natural cortical surface-preserving coarse-graining procedure that in all cases recapitulates a common scale-invariant morphometric trajectory. This indicates these cortices are approximations of a single archetypical fractal shape, differing solely on the range of length scales for which the approximation holds. These results suggest the existence of a universal gyrification mechanism operating on all scales, and that there is only a small number of effective degrees of freedom through which Darwinian natural selection can select cortical shapes. This new way of expressing morphology can be used to parametrize stages of cortical development and aging, and to characterize different conditions such as Zika-induced microcephaly and Alzheimer's. We hope that this systematic approach may help elucidate the processes underlying cortical gyrification in health and disease.

 

[1] Mota B, Herculano-Houzel, S (2015) Science, 349 (6243) 74

[2] Wang Y, Necus J, Kaiser M, Mota B (2016) PNAS 113 (45)

[3] Wang, Y., Necus, J., Rodriguez, L.P. et al. Commun Biol 2, 191 (2019)

[4] Wang, Y.; Leiberg, K.; [...]; Mota, B. Neuroimage, v. 226, p. 117546, 2021

[5] Wang, Y.;  Leiberg, K.; [...]; Mota, B. (2023) 10.48550/arXiv.2209.08066