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What Brainless Jellyfish Teach Us About Sleep

What happens when you force a jellyfish to pull an all-nighter?

We all know that sleep is good for our brains, but some creatures—like jellyfish—have no brains. Researchers at Caltech set out to discover if animals without brains still need sleep, and reveal the results in a recent paper in Current Biology. They faced some challenges, such as figuring out how to tell if a jellyfish is asleep, and that led to questions about how to even define sleep, and how far back in the history of life you have to go in order to find the first snoozing animals.

Using some clever techniques, they were able to determine that yes, jellyfish do appear to sleep.


Is this jellyfish sleeping? It could be! Let’s just say it is.

The researchers carefully monitored the movements of the jellyfish, and noted that activity was greatly reduced during the night. While in this sleep-like state, the jellyfish were also less responsive to stimuli such as a snack of delicious shrimp being dropped in their tank. Furthermore, if they were gradually moved during their slumber, then dropped, they took a while to wake up and start swimming. Finally, when kept awake all night with water pulses, they were sluggish the next day. It may sound like a series of cruel pranks, but the jellyfish sure seemed to react like humans do when you mess with their sleep.

If even ancient brainless animals need sleep, then it must be very important. Most of us humans are more complex than jellyfish, and it’s become clear that lack of sleep is bad for us too.

How bad? Log in to Cambridge Brain Sciences to track your sleep alongside your cognitive performance and find out for yourself.


This post was written by Mike Battista, a staff scientist at Cambridge Brain Sciences.