Syncbox

EEG recordings were conducted with a 64‐channel MR‐compatible EEG system (Brain Products, Gilching, Germany; 0.1–250 Hz hardware band‐pass filter, ±16.38 mV recording range at a 0.5 μV resolution and 5 kHz sampling rate) and an EEG cap with ring‐type sintered silver chloride electrodes with iron‐free copper leads (EasyCap, Herrsching, Germany). Sixty‐one scalp electrodes were arranged based on the international 10–20 system with FCz as reference and ground electrode at AFz. In addition, two electrocardiogram (ECG) electrodes and one vertical electro‐oculogram (EOG) were recorded. An abrasive electrolyte gel (Abralyt 2000, Easycap, Herrsching, Germany) served to keep the impedances of all electrodes below 5 kΩ. The EEG‐sampling was synchronized to the gradient‐switching clock of the MR scanner, to ensure time‐invariant sampling of the image acquisition artifact (SyncBox, Brain Products, Gilching, Germany) (Anami et al., 2003 (link); Freyer et al., 2009 (link)).

In this study, fMRI data were acquired using a Siemens Verio 3.0 Tesla scanner (Siemens, Erlangen, Germany) with a standard 12-channel head coil. A gradient echo planar imaging sequence was used with the following parameters: 34 axial slices, repetition time (TR) = 2700 ms, echo time (TE) = 30 ms, flip angle = 90°, field of view (FoV) = 220 × 220 mm, matrix = 64 × 64, and thickness = 3.4 mm. The acquired voxel dimension was 3.4 × 3.4 × 3.4 mm.
EEG data were acquired with an MR-compatible EEG amplifier (BrainAMP MR, Brain Products, Munich, Germany) at a sampling rate of 5,000 Hz, using 64 electrodes in the extended 10–20 montage, plus one extra electrocardiogram electrode. The 64 electrodes included two electrodes monitoring eye movement, thus the remaining 62 electrodes were used for further analysis. An experienced specialist (L.G.) positioned the EEG caps on the subjects. To ensure valid standard positions, the electrode Cz was placed halfway between the nasion and the inion, and was right-left-centered. The reference was set at the mid-frontal position FCz, and the impedances were kept below 10 kΩ. The data were transmitted via fiber optics outside the scanner room. To facilitate the removal of MR-induced artifacts from the EEG data, the sampling clocks of the EEG and MRI systems were synchronized by the Sync box (Brain Products, Munich, Germany).

The original study is presented in (Timmermann et al. 2023 (link)), however we summarize the relevant acquisition information here. Images were acquired in a 3T MRI (Siemens Magnetom Verio syngo MR B17) using a 12-channel head coil for compatibility with EEG acquisition. Functional imaging was performed using a T2*-weighted BOLD sensitive gradient echo planar imaging sequence with the following parameters: repetition time (TR) = 2000ms, echo time (TE) = 30ms, acquisition time (TA) = 28.06 mins, flip angle (FA) = 80°, voxel size = 3.0 × 3.0 × 3.0mm3, 35 slices, interslice distance = 0mm. Whole-brain T1-weighted structural images were also acquired.
EEG was recorded inside the MRI during image acquisition at 31 scalp sites following the 10–20 convention with an MR compatible BrainAmp MR amplifier (BrainProducts, Munich, Germany) and an MR-compatible cap (BrainCap MR; BrainProducts GmbH, Munich, Germany). Two additional ECG channels were used to improve heart rate acquisition for artifact minimization during EEG preprocessing. EEG was sampled at 5 kHz and with a hardware 250 Hz low-pass filter. EEG-MR clock synchronization was ensured using the Brain Products SyncBox hardware.