Dr. Cecilia Diniz Behn and her collaborators used data from rodent studies to formulate a mathematical model to predict and analyze sleep cycles in humans.
Normal sleep involves a constantly changing cycle of wake periods, rapid eye movement (REM) sleep, and non-rapid eye movement (NREM) sleep. All people experience these three “phases” at some point while sleeping, but the frequencies and tendencies with which they are experienced seem to vary greatly by person.
The data seems to suggest that some of the key factors involved in determining the proportions spent in each stage while sleeping were: the “firing rate” of neurotransmitters in the brain, the levels of adenosine (a nucleoside that promotes sleep), and the random excitatory inputs from other parts of the brain.
Behn used these three main factors as variables to develop formulae to display periods of sleep under certain conditions. As a result, she found that during any given session of sleep the transition between stages was rather cyclical, meaning there are changes between wake, REM, and NREM phases on fairly similar intervals under certain constant conditions. The results of testing the formulae were shown to be quite accurate, as the time predicted in each state by the model was quite close to times actually recorded in each sleep state.
Behn believes that understanding sleep cycles is the first step to learning more about the circadian system This research could also help find a relationship between different sleep cycles, the body’s homeostatic regulation, and the release of orexin neurons (which are meant to excite certain brain cells and promote wakefulness).