Fig. 4

Effects of gyral crest curvature on induced electric fields. R_GMES (radius of the gray matter (GM) envelope sphere ), r_CL (radius of curvature of the gyral crest line, limiting case is r_CL→∞=straight within the xy-plane). Crest line: ridge trajectories on the folded cortex. (a) Normalized peak electric field (E_p) strength versus coil orientation (normalized according to the sphere model with R_GMES = 50 mm). (b) E_p strength (min-normalized) as a function of curvature parameters and coil orientation. (c) Electric field distribution in white matter, with asterisks marking E_p positions and dot-tipped arrows indicating coil orientations. (d) E_p offset distance (Euclidean distance from peak to point beneath coil center) versus coil orientation. (e) Comparison between maximum E_p offset distance (at 0° coil orientation) and chord length of a quarter-circle of the crest line.