The new study, led by Howard Hughes Medical Institute investigator Cornelia I. Bargmann and Yun Zhang, a postdoctoral fellow in Bargmann's laboratory at The Rockefeller University, represents a clear capacity for learning in the laboratory animal C. elegans, a microscopic worm with only 302 neurons. The work suggests that the cellular mechanisms underlying this type of learning have been maintained through evolution, and opens the way for more in depth studies of how learning occurs. The study will be published in the November 10, 2005, issue of the journal Nature.
One of C. elegans' fundamental behaviors is movement toward food based on its sense of smell. In the laboratory, this often means wriggling across a plate full of agar toward a cluster of E. coli. But in its natural environment, the soil, C. elegans encounters an astounding variety of bacteria. As it writhes through its world, the worm might meet up with hundreds of different species of bacteria in as little as five minutes. But while some bacteria make ideal worm food, others are toxic.
"The worm swallows them and then they establish an infection inside the worm's gut and they proliferate there. It's exactly like food poisoning," Bargmann explained. If the worm has ingested enough of the bacteria, it can die quickly, but milder cases allow the worm to live for several days ?and head off in search of better food. So, the researchers surmised, knowing whether or not certain bacteria are toxic is something "worth learning" for the worm.