Do Jellyfish dream of electric Eels?

Quallen schlafen, obwohl sie kein Gehirn haben. Was ziemlich erstaunlich ist, denn man ging davon aus, dass der Schlaf eine komplexe Eigenschaft des Gehirns ist und nichts, dass ein paar verteile Neuronen übernehmen könnten. Oder noch grundsätzlicher: Ein paar verteilte Neuronen in einer etwas dümmlichen Qualle dürften eigentlich sowas wie „Schlaf“ gar nicht nötig haben, da ein nicht vorhandenes Hirn auch nichts verarbeiten muss. Dennoch schlafen Quallen, was auch den Schlaf zu einer sehr viel elementareren biologischen Eigenschaft macht, als er es ohnehin schon war.

Die Tiere dürften allerdings nicht wirklich träumen, da ihr Nervensystem zu rudimentär für einen solch komplexen Vorgang ist. Aber wer weiß? Vielleicht träumen Quallen ja doch von elektrischen Aalen.

Discover Mag: Jellyfish sleep, too
Paper: The Jellyfish Cassiopea Exhibits a Sleep-like State

new research on jellyfish is pushing the origin of sleep even further back down the evolutionary tree, before even the appearance of brains.

It’s long been known that any creature with a central nervous system needs to sleep, but jellyfish are effectively brainless. They do have neurons arranged into a “nerve net” throughout their bodies, but they diverged from us before the appearance of a true brains. Nevertheless, researchers observed three important behavioral components of sleep in the jellyfish, indicating that they must indeed regularly enter a sleep-like state to survive. The finding highlights anew how crucial sleep is for our survival, and indicates that it could be a fundamental property of neurons themselves. […]

This is the first time such a state has been observed in a creature with a primitive nervous system like this, and it wasn’t entirely expected for the researchers. Humans and jellyfish diverged hundreds of millions of year ago, which means that there would need to be strong evolutionary pressures for it to stick around for so long.

“From jellyfish to humans, which is basically as evolutionarily distant as two animals could be, they both have this conserved behavioral state,” says co-author Claire Bedbrook. “[It] really emphasizes how important this state is and also may help us in future hypotheses toward why it is that things sleep.”

Of course, jellyfish look very different than us in terms of their nervous system, so it’s not time to start wondering what jellyfish dream about quite yet. Their nervous system is much more primitive than ours, so while we share the same basic need for nightly Z’s, the process in humans is much more complex.

“The sleep state that was originally the same behavior has evolved and been decorated over time to what it is now in humans where it’s really important for very high level cognitive functions like memory consolidation — things we probably won’t see in jellyfish,” Bedbrook says.