verthepast2decades,significantadvancesinmagneticresonance imaging (MRI) techniques have opened anentirely new field of evaluating regions of neural activitybased on focal metabolic changes. Nuclear medicine studieswithsingle-photonemissiontomographyandpositronemis-sion tomography, over many years, have shown that areas ofbrain activity have increased blood flow, and the ability tomeasure increases in oxygen concentration allows detectionof these regions of activity. Correlating imaging with specificneural activity is referred to as brain mapping. The ability toobserve brain function with MRI during specific tasks andmore recently in the resting state is called functional mag-netic resonance imaging (fMRI).fMRI reveals short-term physiological changes associatedwith active brain functioning, and in this way, fMRI canidentifythedifferentpartsofthebrainwhereparticularmen-tal processes occur and can characterize the patterns of acti-vation associated with those processes. This is a dynamiccomplementary modality to the static structural informationobtainedfromconventionalMRI.fMRIhasanincreasingrolein preoperative planning with delineation of eloquent brainareas in relation to intracranial pathologies. Furthermore,fMRIhasprovidedabetterunderstandingoftheneuralbasisfor major psychiatric disorders, neurologic disorders, andsubstance abuse. Numerous functional studies have identi-fiedneuralprocessingdifferencesoralterationsinfunctionalconnectivity on MRI between patient groups and healthyindividuals, such as regarding Alzheimer’s disease.