Starlet Sea Anemones Can Learn Without Brains


| LAST UPDATE 04/06/2023

By Stanley Wickens
sea anemone learning abilities
Anadolu Agency / Contributor via Getty Images

Learning is a trait that defines life's essence, and every living creature has varying degrees of proficiency, from birds to slime molds.However, recent research suggests that starlet sea anemones have surprisingly sophisticated learning skills.

They manifest the ability to remember the relationship between light and electric pulses. Simon Sprecher, a senior author and neurobiologist at the University of Fribourg, explains, "This is exactly what is called associative learning... proof that even animals without brains are able to display complex behavior thanks to their nervous system." However, not every animal has a brain, but cnidarians like sea anemones and jellyfish have a nerve net that is decentralized. It is generally thought that these creatures learn only in non-associative ways. Sprecher and his colleagues wanted to investigate the starlet sea anemones' capability for associative learning. They performed classical conditioning experiments using light and an electric shock. In classical conditioning, a neutral event is coupled with a biologically substantial consequence in the form of a reward or a negative outcome. The researchers randomly assigned the starlet sea anemones to either paired or unpaired trials in which light and electric pulses were synchronously or asynchronously administered. They trained the creatures using a slight electric shock at the same time as the light or at different intervals. Then, they evaluated each creature's reaction to the light alone.

Starlet Sea animal research
Smithsonian Environmental Research Center, CC BY 2.0 via Wikimedia Commons
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The researchers discovered that 72 percent of the group that previously received the shock in conjunction with the light retracted their tentacles with just the light. This was double the rate of animals that received shocks and light at separate intervals. By employing software to observe body length, the team was also able to monitor the extent of the contraction. Animals trained with the light and shock together showed longer retraction times than the others.

It is still unknown whether cnidarians use the same neurotransmitters or neuromodulators as humans, such as dopamine or serotonin, and it is possible that associative learning evolved independently in these animals. According to the researchers, "In most model organisms, defined neural circuits and molecular mechanisms responsible for specific forms of memories have been identified." They believe that this ability of cnidarians to learn is an example of "embodied cognition" and calls for an investigation into the memory structure of organisms that do not have a typical brain.

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