Constant routine protocol

A constant routine protocol is a common method used in human circadian rhythm research to study endogenous circadian rhythms without the effect of exogenous influences. In the method, subjects are kept in constant conditions for at least 24 hours. These include constant light and temperature, as well as constant semi-recumbent posture. In addition, subjects' food intake is evenly distributed throughout the protocol, and subjects are not allowed to sleep for the duration. While in these conditions, subjects are typically assessed for a number of variables of interest. Two of the most common and best understood of these variables are core body temperature and melatonin.

History

The term was first coined by Mills et al in a 1978 paper describing an experiment to determine the effects of jet lag independent of an individual's behavioral cycle, though the methods involved in a constant routine date back to at least 1947.

The protocol arose from the well established concept in circadian research that the observation of organisms under constant conditions allows for the illumination of endogenous rhythms. In contrast to previous methods, however, the constant routine protocol was developed upon the recognition that several key behaviors exhibiting circadian rhythmicity (including sleep-wake cycle, the behavioral cycle, and the food-intake cycle) also act as masking agents of some endogenous rhythms.

Properties

While constant routine protocols differ between from study to study, they share several key characteristics derived from the

Drawbacks

While use of the constant routine protocol has yielded important results, it is not a protocol without drawbacks. The most important of these results from the sleep deprivation experienced as a necessary part of the protocol. It has been previously shown that sleep deprivation