Trio system

We used a whole‐head magnetoencephalography (MEG) system with 275 axial gradiometers (VSM/CTF systems, Port Coquitlam, Canada) housed in a magnetically shielded room. MEG recordings were sampled at 1200 Hz with an online 300 Hz low‐pass filter. The signal was down‐sampled to 600 Hz afterwards for off‐line analysis. No additional bandpass filtering was applied for any analysis, in order to preserve the possibility to perform analyses in the whole spectrum. All participants were recorded in the supine position. Coils placed at the nasion and the left and right ear canals were used to measure participants' head location relative to the MEG sensors during the experiment. During the recordings, an Eyelink 1,000 eye tracker (SR Research, Ontario, Canada) was used to monitor eye movements and blinks. Additionally, we used a FASTRAK device (Polhemus, VT) to record the head shape of participants with 300 head points relative to the three fiducial points (nasion and the left and right ear canals). In addition to the MEG recordings, a structural magnetic resonance image (MRI) of the participants' brain was acquired using a 3 T Siemens Trio system (Erlangen, Germany) and with a voxel size of 1 mm³. During the MRI acquisition, earplugs with a drop of Vitamin E in place of the coils were used for co‐registration of the MRI and MEG data.

All MR images were acquired by a 3 T Siemens Trio system with a standard 32-channel head coil. The following scanning parameters were used for T2*-weighted echo-planar images (EPI): TR = 2.2 s, TE = 30 ms, FA = 90°, FOV = 200 mm, matrix = 64 × 64, voxel size = 3.4 × 3.4 × 3 mm³. We acquired 36 transversal slices covering the whole brain with a 0.75 mm gap. The functional scanning session resulted in 636 EPI volumes, which lasted for 23.32 minutes. After the functional scanning, high-resolution images (voxel size = 1 × 1 × 1 mm³) of the whole brain were acquired for anatomic co-registration, using a standard T1-weighted 3D sequence (MPRAGE).

All anatomical images were acquired on a 3.0 T Siemens Trio system in the axial plane parallel to the AC-PC line using a 3D MPRAGE sequence (TE/TI/TR = 3.29 m/900 m/2200 m, flip angle = 9, isotropic 1 mm³ voxel, 192 axial slices, matrix size = 256 × 192). The fMRI data for this experiment were acquired in the axial plane using gradient-echo EPI (TR = 2000 m, TE = 30 m, flip angle = 70 deg, 30 slices, slice thickness = 3.1 mm, 3 mm × 3 mm in-plane, matrix size = 64 × 64) (Soloff et al., 2015 (link)).