Magnetic resonance imaging (MRI) uses a magnetic field and radio waves to take pictures of the brain. Functional MRI (fMRI) shows what parts of the brain are used when a task is performed. For the test, the subject lies on a table that can slide in and out of the scanner. A computer screen can be seen from inside the scanner. During the scan, subjects may be asked to do the study task or to lie still for up to 20 minutes at a time.