​Functional brain imaging techniques such as positron emission tomography (PET) or functional magnetic resonance imaging (fMRI) provide a unique opportunity to study the brain at work. These techniques detect metabolic and vascular signals that are coupled to changes in neuronal activity, thus affording the possibility to localize brain areas, changing their level of activity during particular behavioral modalities. They also inform about basal and activated metabolic states, particularly PET, which can monitor with appropriate tracers the metabolic rates for glucose and oxygen, as well as blood flow. With fMRI, in addition to activity changes, it is possible to identify the degree of functional and anatomical connectivity existing between a given brain region, taken as a seed, and other brain areas.