Figure 4: Results of simulations with the murine model.

a,b) I_L = I_R = 0.388 mA. Electric field strength on a plane through the electrodes (viewing towards the anterior direction; L and R in panel a indicate the left and right side of the head for all panels) for tTIS (a) and tACS (b). Maxima in the brain were 383 V/m for $E_{\mathrm{TI}}^{\mathrm{free}}$ and 38 kV/m for $E_{\mathrm{AC}}^{\mathrm{free}}$. The four electrodes (gray) were displayed at a short distance from the head for visualization purposes. The distinct areas with low field strengths are the ventricles. c-f) Current ratios R = I_R/I_L varied from 0.1 to 10 with I_L + I_R = 0.776 mA. c) Percentage of brain tissue with $E_{\mathrm{TI}}^{\mathrm{free}}$ above various limits (limit values indicated in the plot in V/m; total brain volume: 465 mm³). d) $E_{\mathrm{TI}}^{\mathrm{free}}$ for extreme values of R (compare to R = 1 in panel a). See Fig. S2 for corresponding animations with intermediate R for tTIS and tACS. e) Distance of the location of maximum $E_{\mathrm{TI}}^{\mathrm{free}}$ in the brain to the midline (“width”, positive values indicate a location to the right of the midline) and skull surface (“depth”). Lines are not smooth due to the finite size of elements in the model. f) Maximum $E_{\mathrm{TI}}^{\mathrm{free}}$ in left and right motor cortex. Numbered lines indicate ratios that elicited the largest movements in the Grossman et al. (2017) experiments for 1: left forepaw; 2: left whiskers; 3: right forepaw and right whiskers.