The study of memory has always been one of the stranger outposts of science. In the 1950s, an unknown psychology professor at the University of Michigan named James McConnell made headlines—and eventually became something of a celebrity—with a series of experiments on freshwater flatworms called planaria. These worms fascinated McConnell not only because they had, as he wrote, a “true synaptic type of nervous system” but also because they had “enormous powers of regeneration…under the best conditions one may cut [the worm] into as many as 50 pieces” with each section regenerating “into an intact, fully-functioning organism.”
In an early experiment, McConnell trained the worms à la Pavlov by pairing an electric shock with flashing lights. Eventually, the worms recoiled to the light alone. Then something interesting happened when he cut the worms in half. The head of one half of the worm grew a tail and, understandably, retained the memory of its training. Surprisingly, however, the tail, which grew a head and a brain, also retained the memory of its training. If a headless worm can regrow a memory, then where is the memory stored, McConnell wondered. And, if a memory can regenerate, could he transfer it?
Shockingly, McConnell reported that cannibalizing trained worms induced learning in untrained planaria. In other experiments, he trained planaria to run through mazes and even developed a technique for extracting RNA from trained worms in order to inject it into untrained worms in an effort to transmit memories from one animal to another. Eventually, after his retirement in 1988, McConnell faded from view, and his work was relegated to the sidebars of textbooks as a curious but cautionary tale. Many scientists simply assumed that invertebrates like planaria couldn’t be trained, making the dismissal of McConnell’s work easy. McConnell also published some of his studies in his own journal, The Worm Runner’s Digest, alongside sci-fi humor and cartoons. As a result, there wasn’t a lot of interest in attempting to replicate his findings.
David Glanzman, a neurobiologist at the University of California, Los Angeles, has another promising research program that recently struck a chord reminiscent of McConnell’s memory experiments—although, instead of planaria, Glanzman’s lab works mostly with aplysia, the darling mollusk of neuroscience on account of its relatively simple nervous system. (Also known as “sea hares,” aplysia are giant, inky sea slugs that swim with undulating, ruffled wings.)