Continuous MEG cortical signals were collected using a whole-head MEG system with 102 magnetometers and 204 planar gradiometers (Elekta Neuromag TRIUX MEG system, Helsinki, Finland) at a sampling rate of 1000 Hz with DC recordings and on-line lowpass filtered at 330 Hz.
To localize the head before each acquisition, four Head Position Indicator (HPI) coils were attached onto the EEG cap. The EEG cap was compatible with MEG system, thanks to 74 electrodes which were MEG-suited with sintered Ag/AgCl sensors (Brain Products GmbH, Herrsching, Germany). The 3D locations of HPI coils, three cardinal landmarks (nasion, left and right periauricular), EEG electrodes and additional points on the scalp were digitized using a Fastrak system (Polhemus, Colchester, VT, USA). Horizontal electro-oculogram (EOG) was acquired by placing one electrode at each canthus of the eyes, while vertical EOG was acquired by placing one electrode below and another above the right eye. Electro-cardiogram (ECG) was recorded with an electrode on the right clavicle and one on the left lower hip region. EOG and ECG were recorded during experimental sessions with a bandwidth of 0.1–330 Hz.
To localize the head before each acquisition, four Head Position Indicator (HPI) coils were attached onto the EEG cap. The EEG cap was compatible with MEG system, thanks to 74 electrodes which were MEG-suited with sintered Ag/AgCl sensors (Brain Products GmbH, Herrsching, Germany). The 3D locations of HPI coils, three cardinal landmarks (nasion, left and right periauricular), EEG electrodes and additional points on the scalp were digitized using a Fastrak system (Polhemus, Colchester, VT, USA). Horizontal electro-oculogram (EOG) was acquired by placing one electrode at each canthus of the eyes, while vertical EOG was acquired by placing one electrode below and another above the right eye. Electro-cardiogram (ECG) was recorded with an electrode on the right clavicle and one on the left lower hip region. EOG and ECG were recorded during experimental sessions with a bandwidth of 0.1–330 Hz.