## 2 Methods
### TRS Measurement  
We tried to measure Hb concentrations at rest in the bilateral PFC with a two-channel TRS system (TRS-20, Hamamatsu Photonics K.K., Hamamatsu, Japan). Details of this system have been described [11]. Briefly, it consists of three pulsed laser diodes with different wavelengths (761 nm, 791 nm, and 836 nm) having a pulse duration of 100 ps at a repetition frequency of 5 MHz, a photomultiplier tube (PMT; H6279-MOD, Hamamatsu Photonics K.K., Japan), and a circuit for time-resolved measurement based on the time-correlated single photon counting technique. Two optical probes having a pair of source and detector optical fibers each of the two-channel TRS system were attached onto the forehead with a bilateral symmetry using a flexible fixation pad, so that the midpoints between the source and detector positions were 30 mm above the centers of the upper edges of the bilateral orbital sockets. The distance between the source and detector of each probe was set at 40 mm. These positionings of the midpoints are similar to those of the midpoints between electrode positions Fp1/F3 (left) and Fp2/F4 (right) of the international electroencephalographic 10-20 system. MRI images confirmed that the optical probes were located over the dorsolateral and frontopolar areas of the PFC. Based on a simulation study of photon migration in the adult head [12], we believe that the TRS measurements in this study provided the CBO changes in the surface region of the PFC under the two midpoints between the source and detector positions. The TRS system acquired time-resolved reflectances using the two probes. From the acquired time-resolved reflectances, various parameters were obtained assuming that the interrogated forehead tissue was an optically homogeneous semi-infinite medium with the absorption and reduced scattering coefficients of \(\mu_{a}(\lambda)\) and \(\mu_{s}{{}^{\prime}}(\lambda)\) for the wavelength of \(\lambda\), respectively. The time-resolved reflectance \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline  & **HT** & **DM** & **HL** & **HT** & **HT** & **HT** & **HL** & **HT** & **HT** & **HT** & **HT** & **none** & **Total** \\  & & & & **DM** & **HL** & **G** & **G** & **HL** & **HL** & **DM** & **HL** & & \\  & & & & & & & & & **DM** & **DM** & **G** & **G** & & \\ \hline
**CH** & 18 & 1 & 0 & 6 & 6 & 0 & 0 & 6 & 1 & 0 & 0 & 3 & 41 \\
**SAH** & 9 & 0 & 4 & 1 & 3 & 0 & 0 & 3 & 0 & 0 & 1 & 21 \\
**CI** & 16 & 3 & 6 & 12 & 10 & 2 & 2 & 14 & 1 & 1 & 5 & 7 & 79 \\
**HI** & 2 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 1 & 3 \\
**BF** & 16 & 1 & 0 & 4 & 4 & 0 & 0 & 2 & 0 & 0 & 0 & 12 & 39 \\
**others** & 8 & 0 & 0 & 4 & 0 & 0 & 0 & 1 & 0 & 1 & 1 & 4 & 19 \\ \hline
**Total** & 69 & 5 & 10 & 27 & 23 & 2 & 2 & 26 & 2 & 2 & 6 & 28 & 202 \\ \hline \hline \multicolumn{10}{l}{HT = Hypertension, DM = Diabetes Mellitus, HL = Hyperlipidemia, G = Gout CH = Cerebral hemorrhage, SAH = Subarachnoid hemorrhage, CI = Cerebral infarction, HI = Head injury, BF = Born fracture.} \\ \end{tabular}
\end{table} 
Table 1: Clinical profiles of patients. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Age** & **Male** & **Female** & **Total** \\ \hline
**\(\leq\)50** & 11 & 4 & 15 \\
**51–60** & 15 & 8 & 23 \\
**61–70** & 20 & 14 & 34 \\
**71–80** & 19 & 38 & 57 \\
**\(\geq\)80** & 22 & 51 & 73 \\
**total** & 87 & 115 & 202 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Distribution of patient’s age.