Over the past few years, it has become clear that oscillatory dynamics of cortical networks are closely involved in sensory coding, attention, memory and sleep. Although most experimental and theoretical studies have focused on the neocortex, we believe that progress in understanding cortical oscillations can be advanced by also considering the olfactory system--which shares many basic properties with the neocortex and shows similar oscillatory patterns. Besides offering the advantage of a greater experimental tractability, the olfactory cortex might prove to be instrumental in uncovering general functional principles of neocortical oscillations, by virtue of the potentially important role of olfaction during neocortical evolution. In this article, we illustrate how such an evolution-based comparative approach can provide novel insights into neocortical slow-wave sleep oscillations and their relationship to respiration.