306 channel meg system

Neuromagnetic brain activity was continuously recorded with a 306-channel MEG system (Elekta Neuromag, Helsinki, Finland), including 204 orthogonal planar gradiometers and 102 magnetometers. A bipolar horizontal and vertical electrooculogram (EOG) was recorded for the offline detection of eye movements. Additionally, a bipolar EMG was recorded from the extensor digitorum communis (EDC) muscle of each forearm and from the tibialis anterior (TA) muscle of each leg. Four coils were attached to the subject’s head bilaterally on the forehead and behind the ears. The position of these coils, prominent anatomical landmarks (right and left preauricular points and nasion) and some additional points along the subject’s head were digitized (Polhemus Isotrak) to map functional MEG data to individual anatomy. MEG data were digitized at 1000 Hz, band-pass filtered from 0.03 to 330 Hz online, and stored on a computer hard disk. As for the analysis of behavioural data, the response accuracy of each subject was visually inspected on EOG traces using the Neuromag software package (Elekta Neuromag, Helsinki, Finland). MEG data were analysed with Matlab 2012a (Mathworks, Natick, MA, USA) and FieldTrip (http://fieldtrip.fcdonders.nl), a Matlab software toolbox for MEG and EEG analyses [48] . Data from 204 gradiometers were analysed.

In each experiment, participants with normal or corrected to normal vision were seated in a 306-channel MEG system (Elekta, Finland). MEG data were acquired at a sampling rate of 1,000 Hz with a 50-Hz notch filter and 0.1–300 Hz bandpass filters. MEG data were coregistered with each participant's anatomical MRI, obtained using a 3-T MRI system (Siemens Magnetom Trio). This was achieved through surface matching of the MRI with a three-dimensional digitization of the participant's scalp (Fastrak, Polhemus, USA). Head position was monitored throughout, based upon the digitized position of five surface-mounted electromagnetic coils, positioned around the head. Electromyography (EMG), native to the MEG system, was used to record muscle activity from two disk electrodes placed upon the first dorsal interosseous muscle, simultaneously measured with the MEG acquisition.
At the end of the baseline (BL) recording session, participants were administered either oral zolpidem (0.05 mg/kg) or placebo, consistent with previously reported effective subsedative doses (35 (link)). An identical second MEG recording session was initiated 50 min after the zolpidem administration, with participants required to repeat the same rest and movement periods. Participants therefore completed a total of four MEG sessions (BL, zolpidem and BL, placebo).

Patients were recorded during sleep accommodated in supine position with the head fitting a 306-channel MEG system (102 magnetometers and 204 gradiometers, Elekta Neuromag Oy, Helsinki, Finland) at the MEG Center of MSUPE. Data was acquired at a sampling rate of 1000 Hz. Additionally, ECG, EOG and EMG from the right and the left masseter muscles were recorded. Hands and legs movement were tracked with four accelerometers fixed at the index fingers of both hands and the second toe of both feet. Head movements were monitored by four head position indicator (HPI) coils, whose position was constantly tracked during the recordings. The 3 anatomical fiducial points (nasion, left and right preauricular points) also were digitized using FASTRAK system (Polhemus Inc., Colchester, VT, USA) for the MRI-MEG co-registration.