Brain imaging studies with positron emission tomography (PET) or magnetic resonance imaging (MRI) show defects in the network of motor system, in the lateralization of speech areas, and functions of the auditory cortex. Magnetoencephalographic studies describe a similar variety as cause of stuttering. There may be defects in the auditory feedback, a modification of the lateralization of speech areas, or an alteration of co-action of motor planning and auditory system.