EEG recording

EEG was recorded from 56 Ag/AgCl electrodes placed 2.5 cm apart in a grid overlying central and related regions (see insert in Fig. 3). The amplifier upper frequency limit was 50 Hz, the time constant 1 s, and the sampling frequency 128 Hz. The reference electrode was mounted on the right ear and the grounding electrode on the forehead. EOG was recorded from the lateral corners of both eyes. Surface EMG was recorded from the right forearm (m. extensor digitorum communis) with 1 kHz upper frequency limit and 0.1 s time constant. EMG was rectified and full-wave integrated by a contour follower time constant of 0.04 s (see [9]). A photoelectric sensor was placed on the tip of the index finger to indicate onset and offset of movements.