Figure 7:

Bi-layered system to capture cortical folding taking into account the axonal fiber orientation. The top layer, the cortex, has a constant growth rate, while the bottom layer, the subcortex, shows stretch-driven fiber growth in the direction of the axons. Folding patterns emerge for three different axon orientations: curved outward, concentric, normal to the interface (a, left to right). The local Burgers vector density is calculated on the plane normal to $\overline{\mathbf{\text{n}}}={\mathbf{\text{e}}}_3$ and it shows that the incompatibility due to growth occurs mostly at the interface between cortex and subcortex (b). Removing all constraints and external forces, the only residual stress left is due to the incompatible growth field, which shows that the maximum principal stress occurs at the interface between the two layers (c).