Decapitated Worms Regrow Heads, Keep Old Memories

In French Revolution-style, researchers decapitated flatworms—then did something that would give even Madam Defarge the creeps.

The scientists let the worms’ heads grow back and found that their memories returned along with the new noggins, according to a new study in the Journal of Experimental Biology.

Researchers decapitated a flatworm (left), and then allowed its head to regrow (far right). Photograph courtesy Michael Levin and Tal Shomrat, Tufts University

Michael Levin and Tal Shomrat, biologists at Tufts University, have been studying how animals store and process information, whether it’s memories in the brain or the blueprint for developing organs in the body.

The team turned to flatworms because, despite their relative simplicity, they have many of the same organs and body organization as people: a brain and nervous system, bilateral symmetry, and even some of the same behaviors.

Flatworms “also have many of the same neurotransmitters as we do, and have been shown in older studies to remember complex tasks,” Levin said. (Read more about memory in National Geographic magazine.)

Yet unlike people, these worms have a remarkable ability to regenerate organs and body parts, including their brains—making them perfect research subjects.

In the Spotlight

Planarian flatworms are a hugely diverse array of small non-parasitic worms found in both freshwater and saltwater environments.

They have primitive eyes that can detect light, which they generally avoid—being in light makes them more obvious to predators.

To train the worms that lighted areas were safe and contained food, the researchers used a computerized device to continually track the worms’ behavior, providing rewards when a worm ventured into the bright spots and punishments when it remained in the dark.

“We used this device to get worms used to a dish with a peculiar laser-etched surface. When they remember this surface, they will rapidly approach a piece of liver to eat it, as opposed to spending much time circling around the dish to get the lay of the land,” Levin said.

Off With Their Heads

After the team verified that the worms had memorized where to find food, they chopped off the worms’ heads and let them regrow, which took two weeks.

Then the team showed the worms with the regrown heads where to find food, essentially a refresher course of their light training before decapitation.

Subsequent experiments showed that the worms remembered where the light spot was, that it was safe, and that food could be found there. The worms’ memories were just as accurate as those worms who had never lost their heads. (Test your memory with a National Geographic game.)

Memory Beyond the Brain

The obvious question remains: How can a worm remember things after losing its head?

“We have no idea,” Levin admitted. “What we do know is that memory can be stored outside the brain—presumably in other body cells—so that [memories] can get imprinted onto the new brain as it regenerates.”

Researchers have long confined their investigations of memory and learning to the brain, Levin said, but these results may encourage them to look elsewhere. (Read about a tadpole that can see through an eye implanted on its tail.)

“We’ve established a new model system in which our future work will be able to figure out how memories get encoded and decoded to and from living tissues.”

And given that we can’t regrow their heads, it’s unlikely that decapitation will ever become a serious memory aid for frantic students before exams.

Wildlife

Carrie is a freelance science writer living in Virginia. When she's not writing about cool critters, she's spending time outside, drinking coffee, or knitting. You can visit her website at http://www.carriearnold.com