Clinical Cornerstone • SLEEP DISORDERSAND CHRONIC INSOMNIA • Vol. 6, Supplement 1C Sleep Disorders: An Overview Timothy Roehrs, PhD Director of Research Thomas Roth, PhD Chief, Division of Sleep Medicine Sleep Disorders and Research Center Henry Ford Hospital and Department of Psychiatry and Behavioral Neurosciences Wayne State University Schoolof Medicine Detroit, Michigan Although sleep disorders medicine is a relatively young discipline, understanding of the diagnosis, patho- physiology, and treatment of sleep disorders is evolving at a rapid pace. This overview discusses the his- tory of the development of sleep disorders medicine, tracing changes in the diagnostic classification of sleep disorders as well as the role of polysomnography in diagnosis. This evolution is most evident for insomnia, one of the major sleep disturbances. The accumulation of epidemiologic data on the prevalence and temporal course of insomnia and emerging information regarding its pathophysiology derived from laboratory assessments have led to the development of new therapeutic approaches for primary insomnia and insomnia associated with medical and psychiatric disorders. (Clinical Cornerstone. 2004;6[Suppl 1C]:$6-S16) Copyright © 2004 Excerpta Medica, Inc. The diagnosis and treatment of sleep disorders is a relatively new discipline in medicine dating to the late 1970s. The field developed through the emergence of a core of basic scientific knowledge about sleep physiology and pathophysiology. The proliferation of knowledge about basic sleep processes evolved from the discovery of rapid eye movement (REM) sleep by Aserinsky and Kleitman in 1953.1 This discovery was significant in that it showed that sleep comprises 2 dis- tinct brain states, REM and non-REM (NREM), both of which are qualitatively different from wake. Thus, the basic tenet of sleep medicine is that an individual might be healthy while awake, but exhibit pathology during sleep. Later, it became clear that REM and NREM sleep had very different physiologies and mechanisms. 2 Consequently, as was later discovered, the likelihood of expressions of pathology during sleep differs depending on the sleep state. For example, nor- mal breathing patterns and control differ in REM ver- sus NREM sleep, which then has an impact on the like- lihood of sleep-disordered breathing in the 2 sleep states. The normal muscle atonia in REM sleep and the relative loss of hypercapnic drive in REM sleep both increase the likelihood of airway collapse and apnea in REM compared with NREM sleep. With the emergence of basic knowledge about sleep physiology and improved recognition of primary sleep disorders, physicians began to pay increasing attention to patient complaints about disturbed sleep and daytime alertness. Specialized centers dedicated to the diagno- sis and treatment of sleep disorders emerged; at these centers, the continuous physiological monitoring of sleep (polysomnography [PSG]) and other relevant physiological processes could be used to identify sleep disturbances and primary sleep pathologies. Thus, a body of knowledge emerged regarding the characteris- tic cluster of signs and symptoms that are associated with various sleep disorders. In some cases, an under- standing of the pathophysiology underlying the disorder developed. The first association of sleep disorders centers was formed in 1978 in the United States and the first systematic and comprehensive diagnostic classification of sleep disorders was published the next year. 3 $6