EEG was acquired using a 64-channel system that used the SynAmps2 amplifier and Scan 4.3 acquisition software (Compumedics Neuroscan Inc., Charlotte, NC). The EEG signal was referenced to an electrode located between Cz and CPz for online recording, and then re-referenced to the right ear offline. The ground electrode was placed 8 cm above the nasion. Electrode impedances were maintained below 10 kOhms. The SynAmps2 amplifier had a fixed range of ±333 μV sampled with a 24-bit A/D converter where the least significant bit was 0.019 μV. The sampling rate was 250 samples/sec.
