A model of uniform cortical composition predicts the scaling laws of the mammalian cerebrum

The size of the mammalian cerebrum spans more than 5 orders of magnitude. The cortical surface gets increasingly folded and the proportion of white-to-gray matter volume increases with the total volume. These scaling relations have unusually little variation. Here, we develop a new theory of homogeneous composition of the cortex across mammals, validated with three simple numerical models. An extended tension model combined with a fractal-like growth rule, explains the pattern of gyri and sulci, as well as the arrangement of primary and secondary areas on the cortex. The second model predicts the white matter volume. The third model predicts the cortical surface area from the gray and white matter volume. All models have an r2 > 0.995. Further, the last model accurately predicts the intraspecific variation for humans. Except for cetaceans, no clades show systematic deviations from the models, providing evidence that the regular architecture of the cortex shapes the cerebrum.