Figure 1 Measurement process of the distance between the precentral knob and the surface point. (A) The location of target point is determined as the precentral knob, the omega-shaped area in the precentral knob in front of the precentral sulcus (blue arrow), and surface point as the area of the scalp in the vertical direction from the target point (green arrow). (B) The surface point is confirmed on the scalp and in the brain navigator system by the point marker. (C) The horizontal and vertical distances from the midline central (Cz) to the surface point (green arrow) are measured using the brain navigator point marker by placing a 1-cm grid on each subject’s head.