Recorder software

PSG recordings were acquired using a 16-channel, V-Amp 16 system (Brainamp, Brain Products GmbH, Gilching, Germany) from ten scalp derivations (F3, Fz, F4, C3, Cz, C4, P3, Pz, P4, Oz) referenced to linked mastoids (A1, A2). PSG signals were recorded continuously (at <5K Ohm) during the whole night using Recorder software (Brain Products) and were visually inspected online for quality. Signals were digitalized at 250 samples per second (high pass filter = 0.3 Hz, low pass filter = 70 Hz). PSG measurements included EEG, electro-oculogram (EOG), and bipolar submental electromyogram (EMG) electrodes, as well as a nasal airflow thermistor (Braebon, Ottawa, Canada) to monitor respiratory effort.
For all PSG recordings, including online scoring and stimulation periods, sleep stages were visually identified in 30 s epochs displaying EEG (high pass filter = 0.3 Hz, low pass filter = 35 Hz) from central and occipital derivations (C3, C4, and Oz) referenced to average mastoids (A1 and A2), EOG (high pass filter = 0.3 Hz, low pass filter = 35 Hz) from the lateral outer canthus of each eye, and bipolar submental EMG (high pass filter of 10 Hz). Periods of cortical arousal or movement during sleep were identified using an automated detector when movement continuously exceeded 100 μV for more than 100 ms.

Brain Products Recorder software was used. A 64-conductor Ag/AgCl electrode cap extended by the international 10–20 system was used to collect EEG signals. Reference electrodes were placed on the bilateral mastoid connection, and TP9 and TP10 were selected as reference electrodes. A bandpass filter was set for 0.01–100 Hz, with a sampling frequency of 500 Hz/channel. To obtain pure brain waves, impedance of all the electrodes was set below 10kΩ.

This study is based on continuous qEEG signals recorded at bilateral sensorimotor (T7-C3-Cz-C2-T8) and occipital (O3-Oz-O2) sites (Recorder software, Brain Products). The more lateral T7 and T8 electrodes were added to the classical central electrodes (C3-Cz-C4) to include lateral parts of the sensorimotor cortex (Fabbri-Destro and Rizzolatti, 2008 (link)), usually overlooked by previous EEG studies. Data were referenced at FPz and re-referenced offline with bilateral mastoids to reduce eye-blink contamination. Electrical impedance was held below 25 kΩ, as required with active EEG electrodes. Data were sampled at 500 Hz and filtered with bandpass set at 0.01 Hz (high-pass) and 70 Hz (low-pass), and a notch filter for the 60 Hz frequency (North American electrical noise). Signals exceeding ± 100 μV (muscle artifacts) were automatically rejected.