Scientists inserted disco 'strobe lights' into jellyfish to see how they function without brains

Jellyfish may be brainless, yet they can do surprisingly complex things with their simplistic nervous systems. Now, by fiddling with the genes of jellyfish, researchers have devised a way to spy on the animals' inner workings. 

In the new study, the researchers created a model using the jellyfish species Clytia hemisphaerica, a transparent, umbrella-shaped jellyfish with a tube-like mouth at its center. The teeny jellyfish grows to be only 0.4 inches (1 centimeter) in diameter, meaning the team could place the whole jellyfish under the microscope and observe its entire nervous system at once.

While the human brain serves as a centralized control center for the body, jellyfish have no such structure in their nervous systems. Instead, many jellyfish carry a diffuse "net" of nerves that radiates symmetrically from the center of their bodies; in addition, they have a nerve ring that runs around the bottom of the bell — the half-moon-shaped portion of the jellyfish. Some jellyfish lack nerve nets and have only nerve rings, according to a 2013 report in the journal Current Biology, but C. hemisphaerica has both of these structures. 

The big question is, with no centralized control over their movements, how do these teensy jellyfish perform coordinated behaviors? For instance, how do the blobby critters snatch shrimp from the water column and then fold in half to pull the snacks toward their tubular mouths?

Related: From dino brains to thought control — 10 fascinating brain findings 

To answer this question, the team raised a batch of C. hemisphaerica with a genetic modification that coded for a protein called GCaMP, which glows green when it comes into contact with calcium. 

The special glowing protein was inserted into a location in the jellyfish genome so that it only lit up in active neurons, said first author Brandon Weissbourd, a postdoctoral scholar in biology and biological engineering at the California Institute of Technology. "When neurons are active, the amount of calcium [inside the neurons] goes up, so GCaMP becomes more fluorescent. This means that neural activity looks like flashing," Weissbourd told Live Science in an email.