Caenorhabditis elegans are worms that feed on bacteria in the soil, surviving by distinguishing between toxic and nutritious microbes. And they were the star of research done by Cori Bargmann and colleagues on how lifelong memories are formed in young brains.
Soon after birth, animals create lifelong memories in a process called imprinting. It's what allows geese to know who their moms are and for salmon to return to their native stream after spawning.
In humans, the memory formation process is more complex but it has long been established that storing and maintaining a memory long-term depends on how and when the memory was acquired.
The researchers saw that the worms, even with their small, simple nervous systems, were capable of not just recalling things but forming long-term memories as well. For the study, they let worms, both young and adult, learn how to avoid food smells and then analyzed how neural circuits produce memories from the worms' experience.
According to their findings published in the journal Cell, young worms form lasting impressions of their surroundings, remembering their experiences even as adults, which is three days after they were hatched. Adults, on the other hand, can recall the experience for around 24 hours, soon forgetting.
By silencing certain neurons in the worms' brains and then repeating the learning processes, the researchers were able to determine how each nerve cell contributes to forming and retaining a memory. Many neurons are necessary for adult learning and imprinting but cells known as RIM and AIB were specifically crucial to forming imprinted memory when the worms were young.
When the researchers compared brain activity when imprinting versus developing short-term memories, they saw that the two used similar molecular components but certain genes were only required by just one learning type.
Animal brains are generally complex but with worms having just 302 neurons, they were the perfect candidate for assessing neural circuits in place during memory formation and retrieval.
"The most evocative thing about this work is that it reminds us that learning isn't some fancy innovation of a complex brain. It's a fundamental function that any nervous system can perform," said Bargmann.
Xin Jin and Navin Pokala also contributed to the study.