Memories Can Be Injected and Survive Amputation and Metamorphosis

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.” 

Marco Altamirano | NAUTILUS

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? 

McConnell’s work has recently experienced a sort of renaissance.

Perhaps. Swedish neurobiologist Holger Hydén had suggested, in the 1960s, that memories were stored in neuron cells, specifically in RNA, the messenger molecule that takes instructions from DNA and links up with ribosomes to make proteins, the building blocks of life. McConnell, having become interested in Hydén’s work, scrambled to test for a speculative molecule that he called “memory RNA” by grafting portions of trained planaria onto the bodies of untrained planaria. His aim was to transfer RNA from one worm to another but, encountering difficulty getting the grafts to stick, he turned to a “more spectacular type of tissue transfer, that of ‘cannibalistic ingestion.’” Planaria, accommodatingly, are cannibals, so McConnell merely had to blend trained worms and feed them to their untrained peers. (Planaria lack the acids and enzymes that would completely break down food, so he hoped that some RNA might be integrated into the consuming worms.) 

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