MEG was recorded with a 306-channel Elekta Neuromag™ system (Elekta Oy, Helsinki, Finland) located at the MEG Core of Aalto Neuroimaging, Aalto University. The signals were filtered to 0.1–330 Hz and digitized at the rate of 1 kHz. Four head-position indicator (HPI) coils were attached to the subject's scalp for head position estimation and alignment to a common coordinate frame. The visual cues and feedback (see below) were delivered on a screen located approximately 50 cm in front of the subject's eyes by a projector outside the shielded room. During the recording, the raw MEG data were continuously written in 300-ms segments to a network-transparent ring buffer [33 (link),37 (link)] hosted by the MEG acquisition workstation (6-core Intel Xeon CPU at 2.4 GHz, 64-bit CentOS Linux, version 5.3). This buffer was read over a local network connection by another computer (64-bit Ubuntu Linux, version 12.04-LTS), which processed the data in real time using functions implemented in the MNE-Python software [38 (link)] and presented the visual stimuli using PsychoPy version 1.83 [39 (link)].
Neuromag system
Manufactured by Elekta
Sourced in Finland
The Neuromag system is a magnetoencephalography (MEG) device developed by Elekta. It is used for recording magnetic fields generated by neural activity in the brain. The system provides high-resolution data on brain function and structure, enabling advanced neuroscientific research and clinical applications.
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19 protocols using neuromag system
1
Real-Time MEG Data Acquisition and Visualization
2
Resting-state MEG Recording Protocol
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MEG recordings were performed with a 306-channel whole head Elekta Neuromag® system (Elekta Oy, Helsinki, Finland) in a magnetically shielded room (VacuumSchmelze GmbH, Hanau, Germany). The system consists of 102 sensor units, each with two gradiometers and one magnetometer. Four or five head localization coils continuously recorded the position of the head in the MEG helmet. The data were recorded with a 1250 Hz sampling frequency, a low-pass anti-aliasing filter of 410 Hz and a high-pass filter of 0.1 Hz. Recordings were made with closed eyes, and in a supine position, to minimize head movement. A fifteen-minute resting-state interictal recording was used for analysis. Other recordings included a motor task and somatosensory stimulation, but these data were not used in this study. The position of the head localization coils and the shape of the scalp were digitized using a 3D digitizer (Fastrak, Polhemus, Colchester, VT, USA).
3
Multimodal Neuroimaging of Cognitive Processing
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MEG data were acquired using a 306‐channel Elekta Neuromag System (Elekta Oy, Helsinki, Finland) comprising 102 magnetometers and 204 planar gradiometers. Data were sampled at 1,000 Hz after filtering to 0.1–330 Hz. EEG was recorded concurrently using a 64‐electrode Waveguard™ (Advanced NeuroTechnology, Enschede, The Netherlands) MEG‐compatible cap with the reference electrode at the AFz position. Prior to analysis, the EEG signals were re‐referenced to their average value.
To control for eye‐movement‐related artifacts, a pair of electrooculographic (EOG) electrodes placed below the left eye and on the frontal processes of the left zygomatic bone were applied. Head movements were monitored continuously during the recordings using 5 head‐position‐indicator (HPI) coils.
Prior to the MEG recording, anatomical landmarks (nasion and left and right preauricular points), HPI coils and EEG electrode positions, and 100 (+/−5) additional scalp‐surface points were digitized using the Isotrak 3D digitizer (Polhemus Navigational Sciences, Colchester, VT). To ensure roughly equal distances between the scalp and the frontal and occipital sensors, a special cushion was used whenever necessary.
The stimuli were shown on a semi‐transparent back‐projection screen by a projector located outside the shielded room. The distance between a participant's eyes and the screen was 1.25 m.
To control for eye‐movement‐related artifacts, a pair of electrooculographic (EOG) electrodes placed below the left eye and on the frontal processes of the left zygomatic bone were applied. Head movements were monitored continuously during the recordings using 5 head‐position‐indicator (HPI) coils.
Prior to the MEG recording, anatomical landmarks (nasion and left and right preauricular points), HPI coils and EEG electrode positions, and 100 (+/−5) additional scalp‐surface points were digitized using the Isotrak 3D digitizer (Polhemus Navigational Sciences, Colchester, VT). To ensure roughly equal distances between the scalp and the frontal and occipital sensors, a special cushion was used whenever necessary.
The stimuli were shown on a semi‐transparent back‐projection screen by a projector located outside the shielded room. The distance between a participant's eyes and the screen was 1.25 m.
4
Magnetoencephalography Protocol for Noise Reduction
5
Simultaneous MEG-iEEG Monitoring for Epilepsy
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Simultaneous MEG-iEEG recording was performed on the last day of chronic extraoperative iEEG monitoring. MEG was performed using a 306-channel (204-channel planar gradiometer, 102-channel magnetometer), whole-head-type neuromagnetometer (Neuromag System; Elekta-Neuromag Oy, Helsinki, Finland) at sampling rate of 600.615 Hz and with a band-pass filter of 0.1–200 Hz. The same Neuromag System was used to record iEEG. Due to the limitations of the Neuromag System, up to 60 channels of interest were selected and connected to the EEG port of the same neuromagnetometer system. The reference electrode was chosen from one implanted electrode other than the electrodes of interest mentioned above. The sampling rate and band-pass filter of iEEG were the same as those of MEG. To avoid motion artifacts from metallic materials, connectors of electrode-lead wires of iEEG were fixed to the sensor-helmet with adhesive tape, to avoid changes with body movement. To prevent unnecessary magnetization, we also took care not to perform postoperative MRI until completion of this simultaneous recording. Recording times comprised 4–6 sessions of 3–5 min each. Patients were given mild sedation with intravenous injection of thiopental or oral administration of pentobarbital to induce light sleep stage for enhancement of epileptic spikes.
6
Inhibition-related MEG Data Acquisition
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MEG data were acquired using a 306-channel Elekta Neuromag system located in the Center for Biomedical Technology (Madrid, Spain), using an online anti-alias filter between 0.1 and 330 Hz and a 1,000 Hz sampling rate. Environmental noise was reduced using an offline signal space separation method (Taulu and Simola, 2006 (link)), and subject movements were compensated using the same algorithm. The acquired data were segmented into event-related epochs, and artifacted epochs were discarded from subsequent analyses. Only successful inhibitory trials were considered for further analysis. Additionally, only those participants with a performance accuracy (correct inhibitions) higher than 60% were considered for the final sample.
7
Multimodal Neuroimaging Protocol: MEG & MRI
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MEG data were acquired in a magnetically shielded room at a sampling rate of 1000 Hz using a 306-channel (102 magnetometers and 204 planar gradiometers) Elekta Neuromag system (Helsinki, Finland). MEG signals were recorded at a 1 kHz sampling rate and online filtered at a bandwidth of 0.1–330 Hz. Participants' head position inside the helmet was continuously monitored throughout the experiment using 5 head-position indicator (HPI) coils. Six electrode pairs were used to measure horizontal and vertical ocular and cardiac activity. The standard fiducial landmarks (i.e. left and right pre-auricular points and nasion) plus ~ 300 additional points registered over the scalp and eyes/nose contours were digitalized and used to spatially align the MEG sensor coordinates to the native T1 high-resolution 3D structural MRI of each participant. T1s were acquired with a Siemens 3 T magnetom prismafit MR scanner (Siemens, Munich, Germany) in a separate session with the following parameters: echo time = 2.97 ms, non-switching time = 2530 ms, flip angle = 7° and field of view = 256 × 256 × 176 mm3, number of axial slices = 176, slice thickness = 1 mm, in-plane resolution = 1 mm × 1 mm.
8
MEG Data Acquisition and Preprocessing
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MEG data were acquired using a 306‐channel Elekta Neuromag system located in the Center for Biomedical Technology (Madrid, Spain), using an online anti‐alias filter between 0.1 and 330 Hz and a 1000 Hz sampling rate. Environmental noise was reduced offline using the temporal extension of the signal space separation method,28 using the software Maxfilter (v 2.2 Elekta AB, Stockholm, Sweden), and subject movements were compensated using the same algorithm. We used FieldTrip package29 in MatLab environment, for artifact inspection and removal. Finally, the acquired data were segmented into 4‐s epochs of artifact‐free data. The procedure is extensively detailed in the “supporting information materials and methods”.
9
Multimodal Neuroimaging Protocol for Task-Based MEG
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Magnetoencephalography (MEG) data were acquired using an Elekta Neuromag system with 306 channels, at a sampling rate of 1000 Hz. Participants were seated comfortably in the MEG scanner and performed the task after being familiarized with the task procedure. Head position was tracked continuously using four fixed coil positions relative to the nasion and pre-auricular fiducial landmarks. The electrocardiogram was monitored by placing electrodes at both wrists. Saccades and blinks were monitored using recordings from electrodes around one of the eyes to derive the horizontal and vertical electro-oculogram, respectively. Muscle contraction was measured using bipolar electromyography (EMG) recordings at both forearms using electrodes placed ∼4 cm apart over the flexor digitorum superficialis of each arm, with reference electrodes on the lateral epicondyle (as in ref.27 (link))
10
Multimodal Neurophysiological Recording
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