[Sleep in cetaceans].

Over the course of evolution, cetaceans have adapted to sleep in conditions that can be considered extreme for warm-blooded and air breathing animals. Studies of sleep in cetaceans have led to the discovery of an unusual type of sleep called unihemispheric slow wave sleep. The ability of cetaceans to sleep during swimming and to close only one eye at a time are two other features of their sleep, directly related to its unihemispheric nature. Paradoxical sleep in the form it is recorded in all terrestrial mammals is absent in cetaceans. The pattern of sleep in cetaceans allows them to 1) monitor the environment for predators and conspecifics to maintain group coherence, 2) surface regularly for breathing and 3) maintain effective thermoregulation.