Neuromag triux system

Every participant underwent a 5 min “resting state” scan using the Elekta Neuromag TRIUX system using a 1,000 Hz sampling rate and bandpass filter of 330 Hz at recording. To minimize artifacts, participants removed any metallic objects they wore and were asked to refrain from wearing make‐up or hair products which may have metallic residue. For co‐registration to individual's structural MRI and real‐time movement detection purposes, cardinal points were marked at the nasion, right, and left preauricular positions and five head position coils were placed around the head. The location of cardinal points and head position coils were identified using an electronic positioning system. Once placed inside the darkened magnetically‐shielded room, each participant was asked to view a cross‐hair displayed on a screen in front of the scanner, and to let their mind wander freely for the duration of the resting state scan. Artifact correction was performed using the MaxFilter program. Participants also underwent a 3T MRI (GE Medical Systems, Chicago, IL) high resolution T1 scan of the brain (1 × 1 × 1 mm³ voxels, matrix = 256 × 256, FOV = 25.6, flip angle 15°, 180 axial slices, repetition time = 7.8 s, echo time = 3 ms, inversion time = 450 ms) so that the MEG data could be co‐registered brain anatomy.

MEG data (102 magnetometer channels and 204 planar gradiometer channels; sampling rate: 1,000 Hz; band-pass filter: 0.1–330 Hz) were recorded using Elekta Neuromag^® TRIUX™ system (Elekta AB, Stockholm, Sweden) in a magnetically shielded room. The head position with respect to the MEG sensors in the helmet was monitored continuously with five digitized head position indicator (HPI) coils attached to the scalp. Three HPI coils were placed on the forehead and one behind each ear. At the beginning of each MEG recording, the positions of HPI coils were determined by three anatomic landmarks (nasion, left and right preauricular points), which were digitized using the Polhemus Isotrak digital tracker system (Polhemus, Colchester, VT, USA). To allow the co-registration with the MRI template, an additional set of points (>100) randomly distributed over the scalp were also digitized. Electro-oculogram (EOG) signal was recorded with one ground electrode attached to the collarbone and another two diagonally placed electrodes (one slightly above the right eye and one slightly below the left eye).

MEG data was recorded using a 306-channel (204 gradiometers, 102 magnetometers) whole brain Elekta Neuromag TRIUX system (Elekta, Stockholm, Sweden) in a magnetically shielded room. Participants were placed in the supine position for the duration of the experiment. Data was continuously recorded at a sampling rate of 1000 Hz. The head shape of each participant (including nasion and left/right ear canal) was digitised prior to commencing the experiment. Continuous head position indicators (cHPI) were recorded throughout. The frequencies emitted by the cHPI coils were 293 Hz, 307 Hz, 314 Hz and 321Hz. Magnetometer data was excluded from the main analysis as they contained substantial noise that could not be effectively removed or attenuated.

MEG data were recorded on an Elekta Neuromag TRIUX system inside a magnetically shielded room (Vacuumschmelze Ak3b) at a sampling frequency of 1,000 Hz. Data were acquired with low-pass and high-pass filters applied, at 330 and 0.1 Hz respectively.