Jellyfish Don't Have Brains, But They Do Sleep

Source: Live Science

Jellyfish Don't Have Brains, But They Do Sleep

By Stephanie Pappas, Live Science Contributor | September 21, 2017 01:08pm ET

They don't have brains, or even anything more than a rudimentary nervous system, but jellyfish apparently do have bedtimes.

New research finds that jellyfish enter a sleep-like state. If the study, published today (Sept. 21) in the journal Current Biology, is confirmed by future studies, jellyfish are the first-ever animals with no central nervous system to have been observed sleeping. That finding could bolster the theory that sleep is an emergent property of neurons — in other words, sleep might be something that nerve cells connected in a network just do, even without complex organization.

"The real novelty of what we've shown is that this animal that is almost as far away, evolutionarily, from humans and higher animals as you can go, also seems to have this conserved behavioral state" of sleep, said study co-author Claire Bedbrook, a doctoral student in bioengineering at the California Institute of Technology.

The origins of sleep

Sleep is crucial to survival, but no one knows exactly what it does or why it first evolved. A 1995 study in the journal Behavioural Brain Research found that when deprived of sleep completely, rats died within three weeks. Animals as simple as the worm Caenorhabditis elegans, which has just 302 neurons and an extremely simple central nervous system, have been found to exhibit patterns of activity and rest that look an awful lot like sleep.

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