Worms can learn to avoid substrates scented with bacteria that have made them sick in the past, and the neurotransmitter serotonin appears to control this aversion, according to a report this week in Nature. Serotonin also mediates nausea and food aversions in humans, suggesting that the chemical serves as an important, well-preserved link between gut and brain, according to the authors.

"This is the first example of associative learning found in C. elegans," said Ikue Mori of Nagoya University in Japan, who studies learning and memory in the animals. Researchers have characterized all 302 neurons in the worm's nervous system, and their connections with each other, but still know little about how they work together to coordinate complex behaviors. "Now, we are trying to know the function of these circuits – what's going on during learning," said Mori, who was not involved in the current study.


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