Avian Sleep Homeostasis: Electrophysiological, Molecular and Evolutionary Approaches

The functions of sleep remain elusive. Here, we review our current understanding of the evolution and ontogeny of sleep and demonstrate how comparative sleep research has contributed to our greater understanding of why we sleep. For instance, the occurrence of SWS and REM sleep exclusively in mammals and birds may be related to the convergent evolution of heavily interconnected brains and associated cognitive abilities. We discuss results from comparative analyses on mammalian and avian sleep and highlight promising areas for future research. Lastly, we show how changes in sleep across early ontogeny can provide insight into the functions of sleep.