Electroencephalography (EEG) is the measurement of the potential difference between two electrodes attached to the head, as a function of time. Usually, multiple channels are recorded with respect to a-common reference electrode. Since the EEG is generated by electrical activity of the brain, a study of EEG signals may reveal the functioning of the brain. Similarly, the Magneto Encephalogram (MEG), which is the magnetic induction field corresponding to the electrical brain activity, can be recorded to study brain function. Although the generation mechanisms of EEG and MEG are very similar, the measurement of MEG is much more involved than EEG because the magnetic field of the brain is only very weak (O(10¯13 T)). The EEG can be recorded with electrodes and quite common electrical amplifiers, whereas for the MEG one needs SQUIDS (Super Conducting Quantum Interference Device) and usually a magnetically shielded room.
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