Sleep as a biological rhythm: a historical review.

In the early 1960s sleep was generally viewed as a homeostatic system and its circadian rhythm characteristics were unexplored. During this period the maturing field of chronobiology had paid scant attention to sleep as a biological system. In the late 1960s and early 1970s, the concepts and procedures of chronobiology were rapidly incorporated into sleep research. By the 1980s, the conception of sleep as a circadian rhythm had been accomplished. This major and rapid paradigm shift can be attributed largely to the accessibility of the developed area of chronobiology.