Dolphins Sleep Half Awake, Half Asleep


If you have ever seen dolphins at an aquarium, you may have noticed some of them swimming around slowly with their eyes closed. Similar to how some humans sleep walk, dolphins are able to swim while sleeping. You may have notice at that same aquarium some dolphins swimming around with only one eye open. For humans, as well as most other animals, it is normal for both eyes to be closed when asleep. So what does it mean when a dolphin leaves just one eye open? It turns out that this is due to a phenomenon known as unihemispheric sleep, exhibited by migratory birds and aquatic mammals. Unihemispheric sleep refers to a state where one hemisphere of an animal’s brain is asleep while the other stays awake. This allows the dolphin to watch its surroundings with one eye so that it can react quickly to any threat or emergency that may arise. In particular, while their young are small, they will always sleep while keeping the eye facing their child open, literally never letting them out of their sight. Migratory birds, such as sea gulls and albatrosses, also exhibit unihemispheric sleep. They must travel long distances each season, chasing a warm and comfortable climate. Unihemispheric sleep allows them to fly continuously without stopping to sleep.

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Police officers and security guards are required to remain on stand-by for long periods of time, and then react quickly when an emergency arises. If they were capable of unihemispheric sleep, they might be able to rest while maintaining their concentration and ablity to react quickly when necessary. While the structure of animals’ brains do vary somewhat, it is thought that they operate in fundamentally the same way. Therefore, a deeper understanding of the sleep mechanism of dolphins could potentially be useful in developing treatments for human sleep disorders.

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