For a better understanding of AD pathophysiology, functional connectivity is commonly assessed during performance of a cognitive task. However, recently, special interest has been paid to the intrinsic functional organization of brain networks in resting state [12], [14], [16], [36]. The brain resting state is thought to be an energetically costly condition characterized by a rich neural activity and long-range interneuron connections in specific brain circuits (e.g., the default mode network or DMN) that are temporally interrupted or attenuated during performance of sensorimotor or cognitively-demanding tasks [37]. This intrinsic functional organization during rest allows the brain to allocate resources and ready itself for changes or stimuli in internal and external environments. Therefore, the investigation of functional connectivity during resting state rather than during a particular task may reveal an intrinsic functional disintegration between brain regions in AD, and its association with genetic risk factors for this disorder.
