ABSTRACT
In order to understand the origin of rhythmic changes in mental performance, and how the change in individuals on altered sleep-wake cycles, it is necessary to understand body rhythms in general. Mental performance tasks, like core temperature, show rhythms with endogenous and exogenous components, but added complexities exist. These include: the nature of the performance task itself, effects of time awake and sleep loss, the environmental factors that affect performance, and the role of practice. Changes in self-rated subjective feelings and many mental performance tasks have been measured in the daytime in healthy subjects living a conventional sleep–activity schedule. The circadian and time-awake components of mental performance can be separated by a "forced desynchronization" protocol. Even though this protocol is the best way to separate circadian and time-awake effects in mental performance tasks, it is time-consuming and effects due to practice and/or boredom might intrude.
