306 channel

All MEG recordings were obtained in the Magnetoencephalography Laboratory at the Florida Hospital for Children, with a 306-channel Elekta Neuromag TRIUX system in a three-layer magnetically shielded room (Vacuumschmelze GmbH & Co, Germany), following recommended practices for conducting and reporting MEG research (Gross et al., 2013) . The MEG system consists in an array of 204 orthogonal planar gradiometers and 102 magnetometers housed in a head-shaped helmet over 102 locations. During the recordings, participants were in supine position and their heads were covered by the MEG sensor array. Prior to MEG recordings, a 3D digitizer (Polhemus, VT, USA) was used to record the position of fiducial landmarks (i.e., nasion and preauricular points), five head-position-indicator (HPI) coils, and head shape. The individual position of each participant's head relative to the sensor helmet was determined at the beginning and at the end of the recording session, based on the five HPI coils. A closed-loop real-time noise cancellation ("MaxShield", Elekta Neuromag, Helsinki, Finland) was applied during the recordings, and data were acquired at a sampling rate of 1000 Hz with a 0.1-330 Hz band-pass filter.