Chronic insomnia is thought to occur as a result of hyperarousal. While there is a wealth of data to support this position, there is a lack of research to define how hyperarousal interferes with sleep initiation, maintenance, and the perception of sleep quality and quantity. We propose to use Event-related Potential (ERP) techniques to evaluate information processing at sleep onset and during sleep. ERP measures of information processing have been well established in good sleepers; they have not been, however, applied to the problem of insomnia. The goal of the project is to examine the premise that the occurrence and severity of insomnia is fundamentally related to a neurobiologic preparedness to "attend to" and "identify" environmental stimuli. Following an extensive screening, patients with insomnia and good sleepers will participate in two experimental conditions, requiring that they spend four nights in the sleep laboratory over a two week period. ERP data will be gathered prior to, following, and during sleep.