Intrinsic brain activity and resting state networks

Intrinsic brain activity, that is, neural processes unrelated to immediate sensory and motor functions, has been known to exist for nearly a century. However, the physiological functions of this activity remain poorly understood. Resting state functional magnetic resonance imaging (RS-fMRI) has emerged as a major technique for studying the brain’s intrinsic activity. This review briefly discusses the history of related scientific developments antecedent to the discovery of RS-fMRI. Next, the major features of intrinsic activity, as observed using RSfMRI, are presented in some detail. Intrinsic activity is spatio-temporally organized into functional systems known as resting state networks (RSNs). Several aspects of RSNs are discussed, including topographic relations to task-evoked responses, plasticity, state dependence, and development over the lifespan. Several crucial aspects of practical RS-fMRI are discussed, including the problem of artifact and strategies for minimizing the impact of artifact. The last part of this review discusses the current state of RS-fMRI as applied to the study of neurologic and psychiatric conditions.