Net amps 300

Electroencephalogram (EEG) signals were recorded using Net Amps 300 that connects a high-density 128 channel HydroCel Geodesic Sensor Net [18 (link)] (Electrical Geodesics Inc., Eugene, OR) with Net-Station 4.3 software. All electrode impedances were below 50 KΩ before recording was started [19 (link)]. Regions of interest (ROIs) around the parietal-occipital cortex were selected from the following standard international 10/20 posterior parietal electrodes for PO3 and PO4. Electrodes were referenced to the average Cz channel. All signals were anti-aliasing, low-pass filtered at 100 Hz, and digitized at a sample rate of 250 Hz.

The experimental task was presented on a Dell Precision M3800 laptop (2048 × 152 pixels, 60 Hz) using MATLAB (Mathworks, MA, USA) and the Psychophysics Toolbox (Brainard, 1997 (link); Kleiner et al., 2007 ; Pelli, 1997 (link)). EEG signals were acquired with a 128-electrode Hydrocel Geodesic Sensor Net connected to Net Amps 300 (Electrical Geodesics Inc., OR, USA), using NetStation 4.5 software. A photodiode was attached to the monitor to independently verify the timing of stimulus presentation. Participants made their responses using a Cedrus RB-540 response box (Cedrus, CA, USA).

EEG data was recorded using a 128-channel Geodesic Sensor Net and was amplified electronically using a Net Amps 300 instrument (Electrical Geodesics Inc., Eugene, OR, USA). Before each ERP test, all electrode impedances were measured and kept below 50 kΩ. The effective sampling rate was 500 Hz and electrodes with reference to the average signal of all electrodes. Eye movements were recorded using electrodes positioned above and below the right eye and near the left and right outer canthi. The whole task consisted of a total of 750 auditory stimuli with an inter-stimulus interval (ISI) varying from 750–900 ms. To minimize possible artifacts caused by motor responses, in the present study, the participants were instructed and requested to minimize blinking and any bodily movements, subjects were required to keep attention to the auditory stimuli.

The task was presented on a Dell Precision M3800 laptop (2048 × 152 pixels, 60 Hz) using the Psychophysics Toolbox for MATLAB (Brainard 1997 (link); Kleiner et al. 2007 ; Pelli 1997 (link)). EEG signals were collected with 128-channel HydroCel Geodesic Sensor Nets connected to Net Amps 300 (Electrical Geodesics, Inc., OR, USA), using NetStation 4.5 software. A photodiode attached to the monitor independently verified stimulus presentation timing. Participants responded using a Cedrus RB-540 response box (Cedrus, CA, USA).

Neurophysiological data were recorded while subjects were seated in a comfortable arm chair, using a high-density 128-channel EGI system of Net Amps 300 amplifiers [Electrical Geodesics Inc. (EGI), Eugene, OR]. The vertex sensor (Cz) was set as the reference electrode and the sampling rate was 1000 Hz. The impedances of all electrodes were kept below 50 kΩ, as recommended by EGI guidelines. During the recording, patients were instructed to keep relaxed, with their eyes closed, for at least 5 min.
For further off-line processing, 59 electrodes were firstly selected according to the international 10-10 system, and the division of the brain regions is depicted in Figure 1. Then, the recorded EEG was re-referenced using the average of left and right mastoid sensors, and down-sampled to 250 Hz. A notch filter centered at 50 Hz was used to remove the line noise. Other artifact components were automatically rejected by combining ensemble empirical mode decomposition and independent component analysis (Zeng et al., in revision). After that, visual inspection was performed to further eliminate data segments contaminated by noise. Finally, for each subject, epochs of 3 min were segmented for further analysis. The aforementioned pre-processing procedure was performed using the MATLAB Signal Processing Toolbox and EEGLAB (Delorme and Makeig, 2004 (link)).