Ag agcl electrodes

EEG data were recorded using an electrode cap with 64 Ag-AgCl electrodes (NeuroScan Inc., EI Paso, Texas, United States). Electrodes were positioned per the International 10/20 Electrode System, with a reference at left mastoid (M1) and a ground electrode located between FPz and Fz. The EEG data were also acquired from the right mastoid (M2). The horizontal electrooculogram (EOG) was recorded using electrodes placed at the external canthi of each eye. The vertical EOG was recorded using electrodes placed above and below the left eye. Further, the EEG signals were amplified using SynAmps amplifiers. The band-pass filter was set at DC-100 Hz. Furthermore, data from each channel were sampled at a rate of 1,000 Hz. An appropriate amount of electrolyte gel was applied to each electrode to increase the conduction. The electrode impedance level of each channel was kept below 5 kΩ.

Participants were seated in a normally illuminated room. During the WM task, electroencephalograms (EEG) were recorded continuously from 64 scalp locations which were distributed according to the international 10–20 system using Ag/AgCl electrodes (Neuroscan Inc., USA), with an on-line reference to the left mastoid. Signals were re-reference to the average of the left and right mastoid through off-line algebraic computations. Vertical eye movements were monitored by placing electrodes at 1 cm from the outer canthi of each eye, while the horizontal eye movements were monitored by placing electrodes above and below the left eye. Impedance was kept below 5 kΩ. The EEG signals were amplified by a Neuroscan SynAmps² amplifier (Neuroscan Inc., USA) with a bandpass filter of 0.05–100 Hz and digitized at 1000 Hz.
The EEG data were processed offline by Scan 4.3 software (Neuroscan, USA). Ocular artifacts were removed from the EEG signals using a regression procedure built into the Neuroscan software61 (link). The data were digitally lowpass filtered with 30 Hz, and were epoched into periods of 1000 ms (including a 200 ms pre-stimulus baseline) time-locked to the onset of stimuli. Trials with artifacts were rejected using a criterion of ±100 μV.