Decapitated Worms Regrow Heads with Memories Still Inside

Think that memories are in the brain? New research says that may not be exactly true -at least for flatworms. The planarian is fascinating in that it has the ability to regrow body parts when you cut it into pieces -it will even grow a new head if you cut it off! If that's not freakish enough, experiments show that a newly-regrown head can have some knowledge the earlier head learned. Experiments had been don on planarian heads decades ago, with inconsistent results. Tal Shomrat and Michael Levin at Tufts University returned to this idea with state-of-the-art planarian training methods and computerized testing methods. They trained the worms to overcome their distaste of light and rough surfaces to reach food. After two weeks, the trained planarians went straight to the food, unlike a control group of untrained worms.

The worms were relieved of their heads. The scientists made certain that no bit of brain survived. Then, after the worm stumps had painstakingly re-headed themselves, the planarians went back into the testing chamber.

The memory wasn't there right away. But Levin and Shomrat found that if they gave all the worms one quick training session before testing, worms who'd previously been familiarized with rough petri dishes reached the food significantly faster than the other worms. The training session "basically allowed the worms to refresh their memory of what they had learned before decapitation," Levin says. In other words, their memories had survived the loss and regrowth of their heads.

Levin doesn't know how to explain this. He says epigenetics may play a role—modifications to an organism's DNA that dial certain genes up or down—"but this alone doesn't begin to explain it."

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