Signa hdxt excite 3.0 t

A polygonal model of the cortical surface was constructed based on structural MRI (T1-weighted; Signa HDxt Excite 3.0 T; GE Healthcare UK Ltd, Buckinghamshire, UK) using the Freesurfer software (Martinos Center Software)50 (link). To align MEG data with individual MRI data, we scanned the three-dimensional facial surface and 50 points on the scalp of each participant (FastSCAN Cobra; Polhemus, Colchester, VT, USA). Three-dimensional facial surface data were superimposed on the anatomical facial surface provided by the MRI data. The positions of five marker coils before each recording were used to estimate cortical current with VBMEG.
VBMEG is a free software for estimating cortical currents from MEG data (ATR Neural Information Analysis Laboratories, Kyoto, Japan)51 (link)52 (link). VBMEG estimated 4,004 single-current dipoles that were equidistantly distributed on and were perpendicular to the cortical surface. An inverse filter was calculated to estimate the cortical current of each dipole from the selected MEG sensor signals. The hyperparameters m0 and γ0 were set to 100 and 10, respectively. The inverse filter was estimated by using MEG signals in all trials from 0 to 1 s in the offline task, with the baseline of the current variance estimated from the signals from −1.5 to −0.5 s. The filter was then applied to sensor signals in each trial to calculate cortical currents.

MEG data were acquired using a 160-channel whole-head MEG system (MEG Vision NEO, Yokogawa Electric Corporation, Tokyo, Japan). Each participant placed himself or herself in a supine position in a magnetically shielded room, where 5 head-marker coils were attached to his or her face before MEG recording started. Before and after each MEG recording, the positions of the head-marker coils were measured to determine the position and orientation of the MEG sensors relative to the participant’s head. The maximum acceptable difference in position from recording start to recording end was 5 mm. To align MEG data with individual magnetic resonance imaging data (T1 weighted; Signa HDxt Excite 3.0 T, GE Healthcare UK Ltd., Buckinghamshire, UK), we scanned the three-dimensional facial surface and 50 points on each participant’s scalp (FastSCAN Cobra, Polhemus, Colchester, Vermont, USA). The recording-pass band was 0.1–500 Hz, with a sample rate of 2000 Hz.
All participants were instructed to remain awake in a resting state while in the MEG scanner and to keep their eyes closed without thinking about anything in particular. The instruction to keep eyes closed was designed to avoid artifacts from eye blinking. With participants in this state, continuous MEG data were acquired for more than 240 s.