Synamps2 system

EEG signals were obtained through the SynAmps2 System (Compumedics, Neuroscan) in an electrically shielded, sound-attenuated room. Recorded EEG signals were collected using a 32-channel Quick-Cap, which had 30 Ag/AgCl electrodes (FP1, FP2, F7, F3, FZ, F4, F8, FT7, FC3, FCZ, FC4, FT8, T7, C3, CZ, C4, T8, TP7, CP3, CZ, CP4, TP8, P7, P3, PZ, P4, P8, O1, O2, and OZ) mounted on it according to the international 10–20 system and two reference electrodes placed at the opposite lateral mastoids. EEG data were sampled at 500 Hz. To assure the collection of high-quality data, impedance for the previously mentioned channels was kept below 5 kΩ. Horizontal and vertical eye movements were monitored with electrooculogram (EOG) electrodes. Horizontal electrooculogram (hEOG) electrodes were placed above and below the left eye, and vertical electrooculogram (vEOG) electrodes were placed near the outer canthi of each eye. Impedance for the EOG channels was kept below 10 kΩ.
The EEG and EOG signals were baseline corrected and bandpass filtered between 0.3 and 30 Hz. Ocular artifacts were corrected by applying the covariance method with the data from both hEOG and vEOG channels. The data for each were then epoched from −200 to 1,400 ms with reference to stimulus onsets. Extracted epochs were grouped and labeled by trial type (i.e., old, new, and control).

Electrophysiological recordings were acquired using a SynAmps2 system and Scan 4.1 software (Compumedics Neuroscan, Charlotte, NC, USA). Ag/AgCl electrodes hand placed at scalp locations Fz, Cz, Pz, and referenced through the left mastoid (off-line the average of both the right and left mastoids were used as the reference). Forehead served as ground. Measurements were taken in according to the 10–20 international placement guide (Jasper, 1958 ). The recordings were sampled at a rate of 1000 Hz with a 0.1 Hz high-pass and 200 Hz low-pass recording filter. Ocular movements were determined through superior and lateral eye electrodes. Impedances were below 10 kΩ.

EEG activity was recorded using a 32-channel Quik-Cap and amplified with a SynAmps 2 system (Compumedics Neuroscan; Charlotte, NC, USA). The ground electrode was placed on the mid-frontal scalp, and all channels were referred to the left (M1) side of the mastoid. The montage included 6 midline sites (FZ, FCZ, CZ, CPZ, PZ, and OZ) and 12 sites over each hemisphere (Fp1/Fp2, F3/F4, F7/F8, FC3/FC4, FT7/FT8, C3/C4, T3/T4, CP3/CP4, TP7/TP8, P3/P4, T5/T6, and O1/O2). Additional electrodes were employed to monitor ocular artefacts. Electrodes above and below the left eye were used to record the vertical electrooculogram (EOG). The horizontal EOG was recorded from the outer canthus of each eye. The impedance was maintained at or below 5 K before beginning the EEQ acquisition. At each electrode location, continuous EEG activity was sampled at 1000 Hz, amplified with SynAmps 2 AC amplifiers, and digitised at a 24-bit resolution.