A method for assessing nonlinear growth in the fetal cortex

The cerebral cortex is folded into gyri and sulci in the brains of higher mammals. Quantitative study of the process by which the cortex folds during brain development is critical to a complete understanding of normal brain development and neuro-developmental disorders. In this work, we propose a new method by which to localise nonlinearities in the cortical folding process, and thereby identify regions of differential growth across the cortex. Our method is based on spherical harmonic (SPHARM) representation of the cortical surface. Linearity is assessed by comparison of each SPHARM reconstructed surface with an artificial surface constructed using a linear combination of SPHARM coefficients from data at adjoining developmental time points. The resultant quantification of cortical folding development is easy to interpret, and the method has low computational cost. We demonstrate application to a set of experimental MRI data of fetal sheep brains, across key developmental timepoints as the cortex first folds during development.