How to read a jellyfish’s mind

Jellyfish may be brainless, but that didn’t stop these scientists from reading their minds – well, sort of.

Researchers from the California Institute of Technology devised a clever way to tinker with the genes of Clytia hemisphaerica – a tiny, transparent jelly only centimetres in diameter – that makes their neurons glow with fluorescent light, showing exactly which neurons are fired up during different activities.

Remarkably, they think in a fairly well-coordinated manner.

This may help our understanding of whether some forms of thinking are universal across all creatures.

Unsurprisingly, jellyfish are very different to other model organisms, such as mice and fruit flies. Even worms are more closely related to humans than they are to jellyfish.

Jellyfish neurons
Spatial organization of neurons activated when the animal is coordinating behavior. Credit: B. Weissbourd.

“Jellyfish are an important point of comparison because they’re so distantly related,” says Brady Weissbourd, postdoctoral scholar and first author on the study, recently published in Cell.

“They let us ask questions like, are there principles of neuroscience shared across all nervous systems? Or, what might the first nervous systems have looked like?

“By exploring nature more broadly, we may also discover useful biological innovations.

“Importantly, many jellyfish are small and transparent, which makes them exciting platforms for systems neuroscience. That is because there are amazing new tools for imaging and manipulating neural activity using light, and you can put an entire living jellyfish under a microscope and have access to the whole nervous system at once.”

What is a jellyfish brain like?

Instead of having one big central brain, like humans, the jellyfish brain is diffused across its whole body, making it almost net-shaped. This means that each of its parts function independently – if you surgically removed the mouth from the rest of the body, the organ could continue trying to eat.

This unique form of thinking has seen jellyfish endure for hundreds of millions of years – so is obviously a pretty great trait to have. But how does the whole brain network coordinate behaviour?

Well, that’s a question that may be answered with this mind-reading technique.

Jellyfish folds
A jellyfish folds the right side of its body to bring a tiny brine shrimp to its mouth. Credit: B. Weissbourd

Elegant coorperation

By examining the glowing chain reactions in the jellyfish brain network, the researchers identified a neuropeptide (a molecule produced by neurons) that was responsible for causing the jellyfish to fold inwards, allowing it to bring food up to its mouth – an action called umbrella folding.

They also found that the neurons weren’t quite as unstructured as was previously thought and were instead fairly well-organised.

“Our experiments revealed that the seemingly diffuse network of neurons that underlies the circular jellyfish umbrella is actually subdivided into patches of active neurons, organised in wedges like slices of a pizza,” explains senior author David J. Anderson.

“When a jellyfish snags a brine shrimp with a tentacle, the neurons in the ‘pizza slice’ nearest to that tentacle would first activate, which in turn caused that part of the umbrella to fold inward, bringing the shrimp to the mouth.

“Importantly, this level of neural organisation is completely invisible if you look at the anatomy of a jellyfish, even with a microscope. You have to be able to visualise the active neurons in order to see it – which is what we can do with our new system.”

Clytia hemisphaerica
Clytia hemisphaerica from the side. Credit: B. Weissbourd

Seeing is believing, but this is only the first part of the learning journey and only scratches the surface of jellyfish behaviour.

“In future work, we’d like to use this jellyfish as a tractable platform to understand precisely how behaviour is generated by whole neural systems,” says Weissbourd.

“In the context of food passing, understanding how the tentacles, umbrella, and mouth all coordinate with each other lets us get at more general problems of the function of modularity within nervous systems and how such modules coordinate with each other.

“The ultimate goal is not only to understand the jellyfish nervous system but to use it as a springboard to understand more complex systems in the future.”

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