Central Brain Not Required for Learning

I know that jellyfish have more going on than just drifting around till they run into food, but I think I’m not alone in viewing their intelligence as being roughly nonexistent. It never seemed as though there would be any particular point in a jellyfish being able to learn something. Apparently, however, I was wrong. Jellyfish, at least some kinds, are capable of learning:

Even without a central brain, jellyfish can learn from past experiences like humans, mice, and flies, scientists report for the first time on September 22 in the journal Current Biology. They trained Caribbean box jellyfish (Tripedalia cystophora) to learn to spot and dodge obstacles. The study challenges previous notions that advanced learning requires a centralized brain and sheds light on the evolutionary roots of learning and memory.

No bigger than a fingernail, these seemingly simple jellies have a complex visual system with 24 eyes embedded in their bell-like body. Living in mangrove swamps, the animal uses its vision to steer through murky waters and swerve around underwater tree roots to snare prey. Scientists demonstrated that the jellies could acquire the ability to avoid obstacles through associative learning, a process through which organisms form mental connections between sensory stimulations and behaviors.

“Learning is the pinnacle performance for nervous systems,” says first author Jan Bielecki of Kiel University, Germany. To successfully teach jellyfish a new trick, he says “it’s best to leverage its natural behaviors, something that makes sense to the animal, so it reaches its full potential.”

The team dressed a round tank with gray and white stripes to simulate the jellyfish’s natural habitat, with gray stripes mimicking mangrove roots that would appear distant. They observed the jellyfish in the tank for 7.5 minutes. Initially, the jelly swam close to these seemingly far stripes and bumped into them frequently. But by the end of the experiment, the jelly increased its average distance to the wall by about 50%, quadrupled the number of successful pivots to avoid collision and cut its contact with the wall by half. The findings suggest that jellyfish can learn from experience through visual and mechanical stimuli.

“If you want to understand complex structures, it’s always good to start as simple as you can,” says senior author Anders Garm of the University of Copenhagen, Denmark. “Looking at these relatively simple nervous systems in jellyfish, we have a much higher chance of understanding all the details and how it comes together to perform behaviors.”

I never thought I’d be worried about the mental wellbeing of a jellyfish, but it seems that part of this research did involve “isolating” eyes and connecting them to electrodes to measure their reaction to things. If I’m honest, I would have felt bad for the jellyfish before learning that they can learn from their experiences.

On the brighter side, apparently these people can now add “training jellyfish” to their list of skills and accomplishments. Being able to learn is incredibly useful, so in that sense I’m not surprised that creatures whose intelligence I don’t generally consider are capable of it. Now that I’m, thinking about it, I do actually want to know when learning and memory first arose, and whether anything developed the ability to learn, and then later discarded it as a waste of resources. Is it even possible for pattern-recognition in a nervous system to “evolve away”? It kinda seems like one of those evolutionary pathways that only goes in one direction.

Are jellyfish doomed to develop anxiety someday?

Can they feel anxiety now?

Probably not, but what do I know? Until a couple hours ago, I didn’t know they could learn.


  1. xohjoh2n says

    Well, can hydra learn? They’re even simpler but have cells classified as neurons, so I don’t see why they couldn’t.

    But then again, so what? If learning is just a semi-permanently encoded change in response to stimuli based on earlier stimuli, that’s a really bloody low bar to meet.

    OTOH if you expect your jellyfish to pass a written exam on the intricacies of navigation around fake or real mangroves, they’re still out of luck.

  2. wzrd1 says

    If there’s a neural net, learning is possible – even in the body’s “second brain”, the enteric nervous system.
    Ganglion do a fair bit of heavy lifting, as do various types of neurons, using various neurotransmitters and neuromodulators.

  3. xohjoh2n says


    You don’t even need a “neural net”, not as such: if there’s any plasticity whatsoever then something akin to “learning” is possible. Even a single-celled organism can “learn”. (And colonies can definitely do so.)

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