A complementary approach to study resting-state networks is based on the synchrony of spontaneous electrical and magnetic activity of the brain. Oscillating neuronal assemblies are assumed to reflect cognitive processing,32 and generate a fluctuating electromagnetic field that can be detected with scalp electrodes. EEG detects the electrical component of this field with a high temporal resolution (millisecond range) and provides a direct reflection of (large-scale) neuronal activity. Factors that limit the use of EEG are the relatively modest spatial resolution and the difficulty recording subcortical sources of activity. In this regard, MEG provides an important step forward. MEG records the very weak magnetic field around the brain (±100-1000 femtoTesla), which requires advanced equipment including superconducting quantum devices and a magnetically shielded room, but offers clear advantages including higher spatial resolution (±5 millimeters), less artifact interference, and a shorter set-up time without electrodes.33 The EEG and MEG signals are usually analyzed in separate frequency bands: delta (between 0-4 Hz), theta (4-8 Hz), alpha (8-13 Hz), beta (13-30 Hz) and gamma (30-45 Hz).
