Investigation of the Law of Volume Constancy in Cortical Laminae

Decades of research has shown that the cortex contains gyral folds (peaks) which are thicker than the sulcal folds (valleys). This observation led early 1900s scientists to propose that these thickness differences made gyri and sulci functionally distinct regions. However, an anatomist showed that the the layers within the cortex (cortical lamina) maintained their relative volume and neuron composition throughout the curved sections, suggesting that curvature alone is not an indicator of function (Bok 1929 DOI: 10.1007/BF02864437). In this study, we investigated the validity of this "Law of Volume Constancy" in our computational model of cortical folding, including simulations of heterogeneous cortical growth (Wang et al. 2021, DOI: 10.1007/s10237-020-01400-w). To do so, we calculated the average difference in relative laminar volume and thickness between gyral and sulcal folds in both Bok's original analysis and our simulations. The folding simulations maintained their volume within approximately the same error (+/- 3%) as Bok's analysis. However, we determined that the volume preservation was likely a result of the prescribed initial volume and identical initial laminar thickness, thus highlighting the limitations of current soft-tissue growth models in accurately replicating natural growth patterns.