Background: I had often wondered how air-breathing mammals were able to sleep without drowning. Today I decided to do some research...
Main Source: http://whale.wheelock.edu/whalenet-stuff/sleeppage/
Backup Source: http://www.ntra-net.com/2008/09/18/dolphins-sleep-with-half-of-the-brain-awake/
Topic: Animals/Biology
Details: Unlike humans, for dolphins breathing is a voluntary action, rather than being involuntary. Since they breath air and live in water they need to consciously head to the surface to fill their lungs. Dolphins, like any other mammal need to sleep, and rather than lying at the surface, which could leave them open to attack from all manner of predators - they have evolved a rather amazing way of sleeping. With one eye closed, they are able to disconnect one half of their brain from the other and sleep one half at a time.
In laboratories scientists have measured dramatically decreased activity in the sleeping half, whilst the opposite eye is closed. After about 20 minutes or so this is reversed. Dolphins apparently rest this way on and off throughout the day and during these periods, everything inside the dolphin slows down, and the mammal moves very little.
Someone once said to me that dolphins didn't seem very clever to him because all they did all day was play around in the sea. To me that seems VERY clever...
According to the Guinness Word Records the longest anyone has ever held their breath underwater is 8 min 32.59 sec and was achieved by Karoline Mariechen Meyer (Brazil) at the Racer Academy swimming pool, Florianopolis, Brazil, on 10 July 2009.
