Jellyfish, with no Central Brain, Shown to Learn from Past Experience
Published:14 Nov.2023    Source:Cell Press

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..

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.
The team showed the stationary rhopalium moving gray bars to mimic the animal's approach to objects. The structure did not respond to light gray bars, interpreting them as distant. However, after the researchers trained the rhopalium with weak electric stimulation when the bars approach, it started generating obstacle-dodging signals in response to the light gray bars. These electric stimulations mimicked the mechanical stimuli of a collision. The findings further showed that combining visual and mechanical stimuli is required for associative learning in jellyfish and that the rhopalium serves as a learning center. Next, the team plans to dive deeper into the cellular interactions of jellyfish nervous systems to tease apart memory formation. They also plan to further understand how the mechanical sensor in the bell works to paint a complete picture of the animal's associative learning.