Beluga whales have unihemispheric brain waves when they sleep, meaning that one hemisphere of the cerebrum is always active allowing for surfacing to breath.
Studies of brain activity of several odontocete species, including beluga whales, show unihemispheric brain waves when they sleep. This means that one hemisphere of the cerebrum is always active during sleep, allowing them to control surfacing and breathing patterns. The sleeping hemisphere switches with the non-sleeping hemisphere many times during the sleeping period. Cetaceans have the ability to swim while sleeping, but a common resting behavior seen is logging, in which the whale lays still at the surface of the water.