blue circles of Fig. 1) are plugged into a probing holder and arranged as 3 × 11 array, resulting in a total of 52 channels detection with 3 cm source-detector separation, which permitted to measure the regions at the approximate depth of 2 to 3 cm from the scalp that corresponded to the surface of cerebral cortex [31–34]. In order to cover the whole PFC, the optode was positioned by according to the international 10-20 system [35]. Figure 1 indicates the schematic arrangement of the fOT optode array. The bottom row of channels was arranged along the T3–FP1–FP2–T4 line of the international 10-20 system, with sources 11, 13, 14 and 16 exactly at the T3, FP1, FP2 and T4 position, respectively. Furthermore, the detector 26 was fitted around FZ.
