Neuromag meg system

Subjects’ brain activity was recorded using a 306 channels (102 triplets of sensors each composed of 1 magnetometer and two orthogonal planar gradiometers) whole-head Elekta Neuromag MEG system with an acquisition sampling rate of 1 kHz and hardware bandpass filtering between 0.1 and 330 Hz. Prior to installing the subjects in the MEG room, we digitized three head landmarks (nasion and pre-auricular points), four head position indicator (HPI) coils placed over frontal and mastoïdian skull areas, as well as about 60 additional locations over subjects’ skull using a three-dimensional Fastrak system (Polhemus). Thanks to HPI landmarks, head position within the MEG helmet was measured at the beginning of each run. Electrocardiogram, vertical and horizontal oculogram were recorded in order to monitor heart rate and eye movements during the experiment.

Recordings were performed at the Oxford Centre for Human Brain Activity (OHBA) using a 306-channel Elekta Neuromag MEG system comprised of 102 magnetometers and 204 planar gradiometers at a sampling rate of 1000 Hz. The patient was relaxed and seated under the device, and the relative head position was determined and tracked using Standard Elekta-Neuromag head position indicator (HPI) during the scan. Prior to data acquisition, the HPI coil locations, the position of three anatomical landmarks (the nasion, and left and right pre-auricular points), and the head shape were measured using a three-dimensional digitizer (Polhemus Isotrack). Patients were scanned during the n-back task for 12 min in both DRGS-ON and DRGS-OFF conditions, separated by a pre-defined washout period [20 (link)] to prevent carryover effects. Patients were also scanned with the DRGS-OFF at rest with eyes open for comparison with task conditions. Electrocardiographic (ECG) recordings were monitored by applying bilateral electrodes to the volar aspect of the wrists and, simultaneously, electrooculographic (EOG) traces were recorded by two electrodes, placed above and below the left eye.

MEG data were acquired inside a magnetically shielded room with a whole-head, adult-sized 306 channel Elekta Neuromag^® MEG system (Elekta Oy, Helsinki, Finland). Three anatomical landmarks (left and right preauricular points, nasion), five HPI coils, and approximately 100 additional points were digitized along the head surface using Fastrak^® 3D digitizer (Polhemus, Colchester, VT, USA) in order to construct an individual Cartesian head-centric coordinate system. Once the infant was seated calmly in a custom-made chair under the MEG helmet (Figure 1b), MEG data recording began with an analog band-pass filter of 0.03–330 Hz and a sampling rate of 1.2 kHz. During recording, infants were entertained with silent toys while a silent video of baby faces was played in the background. Infants’ head positions in relation to the sensor array were tracked continuously by extracting the magnetic fields emitted by HPI coils at frequencies between 83 and 323 Hz. Any channels with amplitudes lower than a certain level were marked as “flat”, removed (grad = 1 × 10⁻¹³; mag = 1 × 10⁻¹⁵), and reconstructed by applying the signal space separation (SSS) method [51 (link)] during preprocessing.

MRI (T1 and DWI) scans and MEG recordings were acquired from 10 healthy participants in resting-state, with ages between 62 and 77 years old (mean 69, sd 4.17, 3 males, 7 females) from a dataset owned by the Centre of Cognitive and Computational Neuroscience, UCM, Madrid.
MRI-T1 scans were recorded in a General Electric 1.5 Tesla magnetic resonance scanner, using a high-resolution antenna and a homogenization PURE filter (fast spoiled gradient echo sequence, with parameters: repetition time/echo time/inversion time = 11.2/4.2/450 ms; flip angle = 12°; slice thickness = 1 mm, 256×256 matrix, and field of view = 256 mm).
Diffusion-weighted images (dw-MRI) were acquired with a single-shot echo-planar imaging sequence with the parameters: echo time/repetition time = 96.1/12,000 ms; NEX 3 for increasing the SNR; slice thickness = 2.4 mm, 128×128 matrix, and field of view = 30.7 cm yielding an isotropic voxel of 2.4 mm; 1 image with no diffusion sensitization (i.e., T2-weighted b0 images) and 25 dw-MRI (b = 900 s/mm2).
MEG recordings were acquired with an Elekta-Neuromag MEG system with 306 channels at 1000Hz sampling frequency and an online band-pass filtered between 0.1 and 330Hz. MEG protocol consisted of 5 min resting-state eyes closed.
All participants provided informed consent.

MEG data were recorded in a magnetically shielded room with a whole head adult-sized 306 channel Elekta Neuromag® MEG system (Elekta Oy, Helsinki, Finland). Using Fastrak® 3D digitizer (Polhemus, Colchester, VT, USA), we digitized three anatomical landmarks (left and right preauricular points, nasion) to construct an individual Cartesian head-centric coordinate system, five HPI coils and about 100 additional points along the head surface. Data collection began when infants were seated calmly in a custom-made chair under the MEG helmet (Fig. 1b). Research assistants entertained infants with silent toys while a silent video of baby faces was played in the background. MEG data were recorded with an analog band-pass filter of 0.03–330 Hz and a sampling rate of 1.2 kHz. Positions of infants’ heads relative to the sensor array were tracked continuously by extracting the magnetic fields emitted by HPI coils at frequencies between 83 and 323 Hz. Any channels with amplitudes below a certain level were considered ‘flat’, removed (grad = 1e-13, mag = 1e-15), and reconstructed with the signal space separation (SSS) method (Taulu et al., 2005 ) during preprocessing.

Whole‐head MEG recordings were acquired in a magnetically shielded room with normal illumination using a 306‐channel Elekta NeuroMag MEG System (Elekta, Stockholm, Sweden) at the Oxford Centre for Human Brain Activity. A magnetic Polhemus FastTrak 3D system (VT, USA) was used for head localisation. Relative positions of three anatomical landmarks (nasion, left and right auricular points) were measured in addition to relative positions of four head position indicator coils.
MEG data were collected in three separate recordings of 10–12 minutes each. During the short breaks in between, the data were saved while participants remained seated in the MEG chair. MEG data were sampled at 1000 Hz using a 0.03–300 Hz bandpass filter during digitisation of the signal. ECG and horizontal and vertical EOG were recorded. Eye movements were additionally recorded with a video‐based eye tracker at 1000 Hz (EyeLink 1000; SR Research, ON, Canada). A four‐button bimanual fibre‐optic response device was used to collect manual responses.
Stimuli were created with MATLAB (MathWorks, Natick, MA, USA) and presented using Psychtoolbox version 3.0 (Kleiner et al., 2007). Stimuli were back projected (Panasonic PT D7700E, Panasonic, Osaka, Japan) on a 43 × 54.5 cm translucent screen placed 120 cm in front of the participant, with a spatial resolution of 1280 × 1024 and a refresh rate of 60 Hz.