Traditionally, actograms describe phases of activity and rest, but they have also been used to visualize rhythms in protein phosphorylation, gene expression, and hormone secretion.
[1][2] Actograms are commonly used to study the underlying circadian rhythms of animals in fields such as ecology,[3] reproductive biology,[4] and sleep medicine.
[6] The benefit to the double-plotted actogram was that Pittendrigh was able to notice rhythms that extended beyond 24 hours and the existence of two oscillators within organisms.
[7] If there is a clear rhythm in activity that does not correspond to lighting conditions, or exists in constant darkness, the subject is said to be free-running.
[8] An actogram's period shows an organism's activity rhythm in light or dark conditions.
An organism's phase can be influenced by external stimuli, either causing an advance or delay in their period or not affecting it.
The dead zone is the portion of the graph that shows how, after an external stimulus, there is no phase shift seen in the actogram's data and the line approaches y equals zero.