Figure 1. Computational model of the overlying cortex.

(A) Sagittal MRI section with a single nodule in the atrium of the lateral ventricle (left). We estimated radial migration by generating synthetic streamlines linking the ventricular wall and the neocortex. The laplacian vector field is overlaid on MRI with color-coded equipotential propagation from the ventricles to the neocortex (right). (B) This isopotential field allows the generation of streamlines linking the neocortex and ventricles, thereby providing a guideline to estimate the cortex overlying the nodule. We selected those streamlines (white) that intersected with the manually segmented nodules (red); we then counted the number of heterotopic gray matter voxels that intersected with each streamline and projected this number onto the normotopic cortex. Averaging the number of projections across patients provided the group-level map of the overlying cortex (shown in Figure 2). For visualization purpose, streamlines are displayed with 5% opacity.