An MEG (MagnetoEncephaloGram) is a safe, non-invasive method used to measure the magnetic fields in the brain (just as EEG measures the electric field of the brain). The MEG measures brain waves by detecting the magnetic activity of brain cells. The MEG machine looks like a large helmet with a chair underneath it. The participant will sit in the chair with the top of his or her head inside the MEG machine. The participant's face and body will remain outside of the machine.