Decapitated worms lose their heads, but not their minds

Studies show that planarians, or flatworms, can retain parts of their memories even after their heads are cut off

Topics: Science, Biology, worms, insects, research studies, Smithsonian.com, , ,

Decapitated worms lose their heads, but not their minds Blue garden flatworm or Blue Planarian (Credit: Wikimedia/Jacopo Werther)
This article originally appeared on Smithsonian Mag.

Smithsonian Magazine It’s long been known that many species of worms have the remarkable ability to grow back body and even specific organs when they’ve been cut off. But new research by a pair of scientists from Tufts University has revealed that planarians—small creatures, often called flatworms, that can live in water or on land—are capable of regenerating something even more amazing.

The researchers, Tal Shomrat and Michael Levin, trained flatworms to travel across a rough surface to access food, then removed their heads. Two weeks later, after the heads grew back, the worms somehow regained their tendency to navigate across rough terrain, as the researchers recently documented in the Journal of Experimental Biology.

After two weeks, the worms’ heads grew back, along with training they’d received before decapitation. Image via Journal of Experimental Biology/Shormat and Levin

Interest in flatworm memories dates to the 1950s, when a series of strange experiments by Michigan biologist James McConnell indicated that worms could gain the ability to navigate a maze by being fed the ground-up remains of other flatworms that had been trained to run through the same maze. McConnell speculated that a type of genetic material called “memory RNA” was responsible for this phenomenon, and could be transferred between the organisms.



Subsequent research into planarian memory RNA exploited the fact that the worms could easily regenerate heads after decapitation. In some studies, the worms’ heads were cut off and then regenerated while they swam in RNA solutions; in others, as the Field of Science blog points out, worms that had already been trained to navigate a maze were tested after they were decapitated and their heads grew back.

Unfortunately, McConnell’s findings were largely discredited—critics pointed to sloppy research methods, and some even charged that planarians had no capacity for long-term memory—and research in this area lay dormant. Recently, though, Shomrat and Levin developed automated systems to train and test the worms, which would enable standardized and rigorous measures of how the organisms acquired and retained memories over time. And though memory RNA is still believed to be a myth, their recent research has confirmed that these worms’ memories do work in astoundingly bizarre ways.

The researchers’ automated system eliminated bias inherent in human observers by tracking the worms’ movement across the plate by cameras and encoding their locations by computer. Image via Journal of Experimental Biology/Shormat and Levin

The researchers’ computerized system dealt with the worms, from the species Dugesia japonica, in two groups of 72 each. One group was conditioned to live in a rough-bottomed petri dish, with the other in a smooth-bottomed one, for ten days. Both dishes were stocked with ample worm food (small pieces of beef liver), so each group was conditioned to learn that their particular surface meant “food is nearby.”

Next, each group was separately put into a rough-bottomed petri dish with food located only in one quadrant, along with a bright blue LED. Flatworms typically avoid light, so spending time in that quadrant meant that their expectation of food nearby trumped their aversion to light.

As a result of their conditioning, the worms who’d lived in rough containers were much quicker to flock to the lit quadrant. The researchers had the automated system’s video cameras track how long it took for the worms to spend three straight minutes under the lights, and those reared in the rough dishes took an average of six minutes to pass this number, compared to about seven and a half minutes for the other group. This difference showed that the former group had been conditioned to associate rough surfaces with food, and explored these surfaces more readily.

Afterward, all worms were fully decapitated (every bit of brain was removed) and left alone to regrow their heads over the course of the next two weeks. When they were put back in the chamber with the rough surface, the group that had previously lived in the rough dishes—that is, their previous heads had lived in the rough dishes—were still willing to venture into the lit quadrant of the rough dish and spend an extended period of time there more than a minute faster than the other group.

Incredible as it seems, some lingering memories of the rough-surface conditioning seem to have lived on in the bodies of these worms, even after their heads were chopped off. The biological explanation for this is unclear, as The Verge blog notes. Previous research confirmed that the worms’ behavior is controlled by their brains, but it’s possible that some of their memories may have been stored in their bodies, or that the training given to their initial heads somehow modified other parts of their nervous systems, which then altered how their new brains grew.

There’s also another sort of explanation. The researchers speculate that epigenetics—changes to an organism’s DNA structure that alter the expression of genes—could play a role, perhaps encoding the memory (“rough floors = food”) permanently in the worms’s DNA.

In that case, this strange experiment would provide yet another surprising outcome. There may not be such a thing as “memory RNA” per se, but in speculating on the role of genetic material in the retention of these worms’ memories, McConnell may have been on the right track after all.

More Smithsonian.com

More Related Stories

Featured Slide Shows

  • Share on Twitter
  • Share on Facebook
  • 1 of 11
  • Close
  • Fullscreen
  • Thumbnails

    Ten spectacular graphic novels from 2014

    Beautiful Darkness by Fabien Vehlmann & Kerascoët
    Kerascoët's lovely, delicate pen-and-watercolor art -- all intricate botanicals, big eyes and flowing hair -- gives this fairy story a deceptively pretty finish. You find out quickly, however, that these are the heartless and heedless fairies of folk legend, not the sentimental sprites beloved by the Victorians and Disney fans. A host of tiny hominid creatures must learn to survive in the forest after fleeing their former home -- a little girl who lies dead in the woods. The main character, Aurora, tries to organize the group into a community, but most of her cohort is too capricious, lazy and selfish to participate for long. There's no real moral to this story, which is refreshing in itself, beyond the perpetual lessons that life is hard and you have to be careful whom you trust. Never has ugly truth been given a prettier face.

    Ten spectacular graphic novels from 2014

    Climate Changed: A Personal Journey Through the Science by Philippe Squarzoni
    Squarzoni is a French cartoonist who makes nonfiction graphic novels about contemporary issues and politics. While finishing up a book about France under Jacques Chirac, he realized that when it came to environmental policy, he didn't know what he was talking about. "Climate Changed" is the result of his efforts to understand what has been happening to the planet, a striking combination of memoir and data that ruminates on a notoriously elusive, difficult and even imponderable subject. Panels of talking heads dispensing information (or Squarzoni discussing the issues with his partner) are juxtaposed with detailed and meticulous yet lyrical scenes from the author's childhood, the countryside where he takes a holiday and a visit to New York. He uses his own unreachable past as a way to grasp the imminent transformation of the Earth. The result is both enlightening and unexpectedly moving.

    Ten spectacular graphic novels from 2014

    Here by Richard McGuire
    A six-page version of this innovative work by a regular contributor to the New Yorker first appeared in RAW magazine 25 years ago. Each two-page spread depicts a single place, sometimes occupied by a corner of a room, over the course of 4 billion years. The oldest image is a blur of pink and purple gases; others depict hazmat-suited explorers from 300 years in the future. Inset images show the changing decor and inhabitants of the house throughout its existence: family photos, quarrels, kids in Halloween costumes, a woman reading a book, a cat walking across the floor. The cumulative effect is serene and ravishing, an intimation of the immensity of time and the wonder embodied in the humblest things.

    Ten spectacular graphic novels from 2014

    Kill My Mother by Jules Feiffer
    The legendary Pulitzer Prize-winning cartoonist delivers his debut graphic novel at 85, a deliriously over-the-top blend of classic movie noir and melodrama that roams from chiaroscuro Bay City to Hollywood to a USO gig in the Pacific theater of World War II. There's a burnt-out drunk of a private eye, but the story is soon commandeered by a multigenerational collection of ferocious women, including a mysterious chanteuse who never speaks, a radio comedy writer who makes a childhood friend the butt of a hit series and a ruthless dame intent on making her whiny coward of a husband into a star. There are disguises, musical numbers and plenty of gunfights, but the drawing is the main attraction. Nobody convey's bodies in motion more thrillingly than Feiffer, whether they're dancing, running or duking it out. The kid has promise.

    Ten spectacular graphic novels from 2014

    The Motherless Oven by Rob Davis
    This is a weird one, but in the nervy surreal way that word-playful novels like "A Clockwork Orange" or "Ulysses" are weird. The main character, a teenage schoolboy named Scarper Lee, lives in a world where it rains knives and people make their own parents, contraptions that can be anything from a tiny figurine stashable in a pocket to biomorphic boiler-like entities that seem to have escaped from Dr. Seuss' nightmares. Their homes are crammed with gadgets they call gods and instead of TV they watch a hulu-hoop-size wheel of repeating images that changes with the day of the week. They also know their own "death day," and Scarper's is coming up fast. Maybe that's why he runs off with the new girl at school, a real troublemaker, and the obscurely dysfunctional Castro, whose mother is a cageful of talking parakeets. A solid towline of teenage angst holds this manically inventive vision together, and proves that some graphic novels can rival the text-only kind at their own game.

    Ten spectacular graphic novels from 2014

    NOBROW 9: It's Oh So Quiet
    For each issue, the anthology magazine put out by this adventurous U.K.-based publisher of independent graphic design, illustration and comics gives 45 artists a four-color palette and a theme. In the ninth issue, the theme is silence, and the results are magnificent and full of surprises. The comics, each told in images only, range from atmospheric to trippy to jokey to melancholy to epic to creepy. But the two-page illustrations are even more powerful, even if it's not always easy to see how they pertain to the overall concept of silence. Well, except perhaps for the fact that so many of them left me utterly dumbstruck with visual delight.

    Ten spectacular graphic novels from 2014

    Over Easy by Mimi Pond
    When Pond was a broke art student in the 1970s, she took a job at a neighborhood breakfast spot in Oakland, a place with good food, splendid coffee and an endlessly entertaining crew of short-order cooks, waitresses, dishwashers and regular customers. This graphic memoir, influenced by the work of Pond's friend, Alison Bechdel, captures the funky ethos of the time, when hippies, punks and disco aficionados mingled in a Bay Area at the height of its eccentricity. The staff of the Imperial Cafe were forever swapping wisecracks and hopping in and out of each other's beds, which makes them more or less like every restaurant team in history. There's an intoxicating esprit de corps to a well-run everyday joint like the Imperial Cafe, and never has the delight in being part of it been more winningly portrayed.

    Ten spectacular graphic novels from 2014

    The Shadow Hero by Gene Luen Yang and Sonny Liew
    You don't have to be a superhero fan to be utterly charmed by Yang and Liew's revival of a little-known character created in the 1940s by the cartoonist Chu Hing. This version of the Green Turtle, however, is rich in characterization, comedy and luscious period detail from the Chinatown of "San Incendio" (a ringer for San Francisco). Hank, son of a mild-mannered grocer, would like to follow in his father's footsteps, but his restless mother (the book's best character and drawn with masterful nuance by Liew) has other ideas after her thrilling encounter with a superhero. Yang's story effortlessly folds pathos into humor without stooping to either slapstick or cheap "darkness." This is that rare tribute that far surpasses the thing it celebrates.

    Ten spectacular graphic novels from 2014

    Shoplifter by Michael Cho
    Corinna Park, former English major, works, unhappily, in a Toronto advertising agency. When the dissatisfaction of the past five years begins to oppress her, she lets off steam by pilfering magazines from a local convenience store. Cho's moody character study is as much about city life as it is about Corinna. He depicts her falling asleep in front of the TV in her condo, brooding on the subway, roaming the crowded streets after a budding romance goes awry. Like a great short story, this is a simple tale of a young woman figuring out how to get her life back, but if feels as if it contains so much of contemporary existence -- its comforts, its loneliness, its self-deceptions -- suspended in wintery amber.

    Ten spectacular graphic novels from 2014

    Through the Woods by Emily Carroll
    This collection of archetypal horror, fairy and ghost stories, all about young girls, comes lushly decked in Carroll's inky black, snowy white and blood-scarlet art. A young bride hears her predecessor's bones singing from under the floorboards, two friends make the mistake of pretending to summon the spirits of the dead, a family of orphaned siblings disappears one by one into the winter nights. Carroll's color-saturated images can be jagged, ornate and gruesome, but she also knows how to chill with absence, shadows and a single staring eye. Literary readers who cherish the work of Kelly Link or the late Angela Carter's collection, "The Bloody Chamber," will adore the violent beauty on these pages.

  • Recent Slide Shows

Comments

Loading Comments...