Which theories on sleep ultradian cycling are favored by the positive links found between the number of cycles and REMS?

Abstract

Theories still compete nowadays to explain the sleep ultradian cycling between rapid eye movement sleep (REMS) and non-rapid eye movement sleep (NREMS), both in monophasic and polyphasic sleep organizations. Predictions on which of these theories is the most heuristic can be made on the basis of the relationships between the number of alternations and the respective durations of REMS and NREMS. Links having been found in humans and rodents between the number of cycles and REMS favor hypotheses that make this sleep state the central tenet of the ultradian cycling process. On the basis of these conclusions, a comprehensive hypothesis is proposed on how things could work. The proposal is then discussed at the light of most of the evidence available in the field.