Despite the magnitude of the problem of Primary Insomnia, and the good efficacy of Cognitive Behavioral Treatment for Insomnia (CBT-I), little is known about the pathophysiology of insomnia or whether treatment alters the factors that are thought to maintain chronic insomnia. Three main factors have been explored as contributing to chronic insomnia: hyperarousal, circadian dysrhythmia, and homeostatic dysregulation. Most of the empirical work has been related to the role of hyperarousal along three dimensions: somatic, cognitive, and cortical.