The learning ability of jellyfish: Challenging neuroscience concepts
Even without a central brain, jellyfish, like humans, mice and flies, can learn from past experiences, scientists first report in the journal Science on September 22. current biology. They trained box jellyfish in the Caribbean (Tripedaria cystophora) Learn how to spot and avoid obstacles. This study challenges previous notions that advanced learning requires a centralized brain and sheds light on the evolutionary roots of learning and memory.
Complex vision of simple creatures
No bigger than a fingernail, these seemingly simple jellies have a complex visual system with 24 eyes embedded in their bell-like bodies. These animals, which live in mangrove swamps, use their vision to navigate through murky water and bypass underwater tree roots to capture prey. Scientists have demonstrated that jellies can acquire the ability to avoid obstacles through associative learning. Associative learning is a process by which organisms form mental connections between sensory stimuli and actions.
“Learning is the best performance for the nervous system,” said lead author Jan Bielecki of the University of Kiel in Germany. To successfully teach jellyfish new tricks, he says, “it’s best to exploit their natural behaviors, behaviors that make sense for animals, to maximize their potential.” .
Simulated learning environment
To recreate the jellyfish’s natural environment, the researchers decorated the circular tanks with gray and white stripes, the gray stripes mimicking the roots of distant mangroves. They observed jellyfish in an aquarium for seven and a half minutes. Initially, the jelly swam close to this seemingly distant stripe, frequently bumping into it. However, by the end of the experiment, Jelly’s average distance to the wall increased by about 50%, she made four times as many successful pivots to avoid collisions, and her contact with the wall was reduced by half. . The findings suggest that jellyfish can learn from experience through visual and mechanical stimulation.
Caribbean box jellyfish live and feed in the roots of underwater mangroves.Credit: Anders Graham
“If you want to understand complex structures, it’s a good idea to start as simple as possible,” says lead author Anders Garm of the University of Copenhagen, Denmark. “When you look at these relatively simple nervous systems of jellyfish, you have a much better chance of understanding all the details and how it works together to perform its actions.”
Decoding the learning center
The scientists then sought to identify the processes underlying associative learning in jellyfish by isolating the jellyfish’s visual sensory center called the roparia. Each of these structures has six eyes and generates pacemaker signals that control the pulsating movements of the jellyfish. This signal increases in frequency when the jellyfish veers away from an obstacle.
The researchers showed that a stationary rhopalium moved a gray bar, mimicking an animal approaching an object. The structure did not respond to the light gray bars and interpreted them as distant. But when the researchers trained Rhopalium by giving it weak electrical stimulation when a bar approached, it began producing signals to avoid obstacles in response to the light gray bar. These electrical stimuli mimicked the mechanical stimulation of a collision. The findings further showed that associative learning in jellyfish requires a combination of visual and mechanical stimuli, and that the rhopalium functions as a learning center.
Our goal
Next, the researchers plan to dig deeper into the cellular interactions of the jellyfish’s nervous system to uncover memory formation. They also plan to further understand how Bell’s mechanical sensors work to paint a complete picture of associative learning in animals.
“It’s amazing how fast these animals learn. It’s about the same pace as evolved animals,” Garm says. “Even the simplest nervous systems appear to be capable of advanced learning, and this may turn out to be a very basic cellular mechanism invented at the dawn of evolutionary nervous systems.”
For more information on this research, see Jellyfish’s amazing intelligence changes fundamental understanding of the brain.
Reference: “Associative learning in the box jellyfish Tripedalia Cystophora” September 22, 2023 current biology.
DOI: 10.1016/j.cub.2023.08.056
This research was supported by the German Research Foundation (DFG, German Research Foundation), the Danish Research Council (DFF), and the Vilam Foundation.