With more than 40 years experience in the field of basic and applied research on the physiology of the human circadian timing system and its relationship to the sleep-wake cycle, Dr. Czeisler is interested in the physiology of the hypothalamic circadian pacemaker in humans, photic and non-photic synchronizers of the human circadian pacemaker, temporal dynamics in neuroendocrine systems, homeostatic and circadian factors in the regulation of sleep and alertness, and the application of circadian physiology to occupational medicine/health policy, particularly as it relates to the extended duration work shifts and long work weeks.