Figure 1.
Subjects retired to bed at 01:00 A.M. in the laboratory and were forcibly awakened at 07:00 A.M. by an experimenter. The average duration of actual sleep period was 5.53 h (SEM: 0.05 h). Subjects started working memory (WM) tasks with f-NIRS acquisition 2 h after forced awakening at 09:00 A.M. and were kept awake before the WM tasks commenced. Subjective alertness level was evaluated immediately before and after the experiment using the Stanford Sleepiness Scale (SSS). WM tasks took between 15 to 30 minutes to complete.
Figure 2.
Approximate position of the probe holder.
The distance between the pair of emission and detector probes was 3.0 cm, and it was considered that the machine could measure points at a depth of 2–3 cm from the scalp. A 3×5 (6×12 cm) probe holder was placed on the scalp surface covering the bilateral prefrontal cortex. The measurement points were labeled channels 1 to 22 from right-side top to left-side bottom.
Figure 3.
Correlation of change in Stanford Sleepiness Scale (SSS) level with reaction time.
The horizontal line shows the difference in SSS level between the pre- and post-tasks. Positive values reflect the subject was awakened while performing the task. Blue circles denote 0-back task and red triangles denote 2-back task.
Figure 4.
Numbers indicate the probes. Red upright triangles denote positive correlations and blue inverted triangles denote negative correlations. (A) Correlation of z-score and change in SSS level for the difference between 2- and 0-back tasks for each channel. (B) Correlation of z-score and change in SSS level for 22 channels on the 0-back task. (C) Correlation of z-score and change in SSS for 22 channels on the 2-back task.
Figure 5.
Correlation of z-score and change in SSS level on both the 2- and 0-back tasks for channel 10.
Horizontal line shows the difference in SSS level pre- and post-experiment. Positive values reflect the subject was awakened while performing the task. Blue circles denote 0-back task and red triangles denote 2-back task.