Experiment

The rats had electrodes implanted on their scalps at 5 weeks of age, then were allowed to recover for 5–7 days after electrode implantation. After the recovery from surgery, EEG recording was done at 6–7 weeks of age. Six EEG electrodes were implanted on the left and right frontal (±2.0 mm lateral and 3.2 mm anterior from the bregma), parietal (±3.5 mm lateral and 1.8 mm posterior from the bregma) and occipital cortex (±2.0 mm lateral and 5.2 mm posterior from the bregma) of the rodents’ scalps. The left occipital cortex electrode was used as a reference. With this set-up, five time series of EEG recordings were obtained. The time series of EEG signals were recorded for 1.0–1.5 hours each day according to the protocol devised (see Fig. 1). Eight experiment days were considered: no agent administration on Day 0, vehicle (saline) on Day 1, 0.3 [mg/kg] of MPH on Day 2, 1.0 [mg/kg] of MPH on Day 3, 3.0 [mg/kg] of MPH on Day 4, 1.0 [mg/kg] of ATX on Day 5, 2.0 [mg/kg] of ATX on Day 6, and no agent administration on Day 7. This provided a total of five time series of eight experimental conditions for each individual animal.

Experimental procedure and signal acquisition. (A) EEG signals of each animal were recorded 10 minutes before and 60–90 minutes after injection of medication. No medication was administered on days 0 and 7. Day 4 was followed by a two-day washout period. (B) Schematic layout of electrode locations, left occipital (LO) electrode was used as a reference.