UCLA

Biological time-keeping mechanisms play fundamental roles in the regulation of behavior and physiology, disruption of which can lead to increased incidence of many disorders. Consequently, these mechanisms continue to be investigated intensively. For almost four decades they have been known to be able to store and program complex behaviors, and to be susceptible to the influences of light and day length. Yet present-day research concerns almost exclusively the means by which circadian and lesser time intervals are measured. Even within this narrow focus disagreements exist. Some early studies of small nocturnal rodents and primates running in exercise wheels illustrate the program-clock-like capabilities of endogenous time-keeping mechanisms and their degrees of susceptibility to external influences, such as artificial twilights and shortened light cycles. Broadening perspectives for research on biological clocks to take into account these often overlooked capabilities and susceptibilities could lead to a deeper understanding of them. (c) 2006 Elsevier Ltd. All rights reserved.