2.4. Daytime EEG and HRV Measurement
blinks
EEG and HRV measurements were conducted in a shielded room during the last week of each period: in the pre-intervention period and in intervention periods I and II. Participants underwent measurements on any day from Tuesday to Thursday in the morning (8:00–11:00) and in the afternoon (15:00–18:00). Each measurement required about 1 h, including preparation and cleanup, and the day and time of each individual’s measurements were matched between the experimental periods. We instructed the participants not to consume alcohol for at least 24 h before the measurement and caffeinated beverages on the day of measurement and confirmed the participants’ adherence to the instructions before the measurement.EEG signals were recorded with Ag/AgCl electrodes placed on the scalp at the Fz, Cz, and Pz positions according to the International 10–20 System. Two electrodes placed on both ears were regarded as a reference for the scalp electrodes, and two forehead electrodes served as the ground and system reference. To aid in the elimination of data obtained during eye movements or blinks, an electrooculogram (EOG) was recorded with an electrode placed 2 cm lateral to the lateral canthus of the left eye and 2 cm above the upper edge of the left orbit. Electrodes were also attached to the left arm to monitor the electrocardiogram (ECG) for HRV analysis. EEG and ECG were recorded using a PolymateThe procedure for each measurement is shown in 