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
  [flatworm picture] 
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
an-body/brain-article/>  or the blueprint for developing organs in the

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

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

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

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
-eyeball-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.

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