All animals, including humans, use sleep as a method of recharging their brain and getting ready for another day. But is this really the only purpose of sleep? Scientists have started asking such questions after they found out jellyfish also enter a state similar to sleep. This is unusual since they do not have any brains to put to rest.
Jellyfish become less active at night
As they were studying the behavior of upside-down jellyfish, also known as Cassiopeia, researchers observed how they became less active during nighttime. They entered a state similar to sleep, where they responded less at the external stimuli. This observation became easier thanks to another behavior exhibited by the jellyfish, namely their pulsations.
Researchers saw how the pulsations reduced their volume by one-third at night, as compared to the intense activity of daytime. However, jellyfish were quick to switch from this sleep-like state to wakefulness if they perceived any external excitant. For instance, dropping food in their fish tank brought them back into activity instantly.
Researchers now want to complete the sleep puzzle
Jellyfish showed the exact same behavior as humans when deprived of sleep. In this case, they were less active and offered slow responses to general stimuli both during daytime, and if something perturbed their sleep. These findings are of great value while studying the evolution of sleep, indicating this resting state had appeared in animals before they developed a central system.
Paul Sternberg, one of the researchers involved in the study, said these findings complete the missing pieces of the sleep evolution puzzle.
“It’s the first example of sleep in animals without a brain.”
However, the puzzle is not complete. Since animals without a nervous system sleep as well, it means its purpose might not only be to let the brain rest. Researchers want to see if sleep can have other functions as well. For example that of maintaining the health of cells, or of improving other body functions. All the other findings have been published in the journal Current Biology.
Image Source: Flickr