To help us interpret the MEG magnetic field readings, at a volunteer's first visit we will also use magnetic resonance imaging (MRI) to create an image of his/her brain. MRI is a technique that uses magnetic fields to align the spinning of atoms in water molecules. It then creates an image of the brain and its activity from the tiny amounts of energy released when the atoms relax to their normal state. Structural MRI will give us information about the anatomy of the brain.