Interacting circadian and homeostatic processes with opportunity cost: A mathematical model of sleep with application to two mammalian species.

This paper introduces a new model of sleep for mammals. It extends the classic 'two-process' model of sleep to account for differences in external circumstances. We apply this model to previously-collected data on elephants and sloths, comparing sleep patterns in the wild with sleep patterns in captivity. We find that the model does very well in explaining sleeping patterns for both types of animals, in both the captive state and in the wild state.