Are Memories Transferable? Meet the Scientists Replicating an Infamous Study to Find Out

The archetypal version of this story appeared in Quanta Magazine.

It was the dormant of wintertime successful Boston. The aboveground of the Charles River was frozen solid. But Zachary Kelso braved the biting acold to yet enactment to remainder a enigma that has haunted neuroscience labs for implicit fractional a century.

To bash that, Kelso, a probe adjunct successful the Harvard laboratory of the neuroscientist Sam Gershman, needed some worms. Specifically, planarians: arrow-headed flatworms, which are among the simplest creatures to possess a brain and a tense strategy with bilateral symmetry similar ours. Normally, labs bid these wide utilized exemplary organisms from biologic proviso companies. But the mail-order worms weren’t up to snuff. So Gershman had dispatched Kelso to the Charles’ icy banks to drawback immoderate chaotic ones. “I thought, ‘I’m going to look brainsick due to the fact that I’m utilizing a hammer to bushed done the ice,’” Kelso recalled. “So I wore the much concern extremity of concern casual.”

It wouldn’t beryllium the past clip Kelso recovered himself successful this situation. The Charles River planarians, it turned out, didn’t chopped it either. Neither did the worms helium sourced portion stream-hopping astir Eugene, Oregon, successful March 2025. Nor did the ones helium fished from Michigan lakes that June—this clip successful thigh-high waders—while picnicking families gawked from shore. Kelso diligently turned implicit rocks, angled with bits of nutrient tied to a string, and adjacent followed maps from a vintage guidebook called The Fresh-Water Triclads of Michigan. But his escapade was fruitless. Sure, helium caught plentifulness of planarians. But backmost successful Gershman’s lab, nary of them would bash what they were expected to do.

In the 1960s, an eccentric behavioral scientist named James McConnell convinced the scientific establishment that planarian worms, similar Pavlov’s dogs, could beryllium classically conditioned—and that memories of this grooming could beryllium transferred from worm to worm done cannibalism. These bizarre findings were replicated by different scientists, and worm grooming became a staple of precocious schoolhouse subject fairs. Now, 60 years later, the worms person stopped learning, and cipher knows why.

I archetypal learned astir this technological enigma portion reporting different portion astir what a compartment tin remember. As I dug into the humanities lit connected representation research, I kept coming crossed McConnell’s unusual worm experiments, which captivated a procreation of scientists earlier disappearing entirely. Planarian representation had itself been forgotten. I was contented to disregard it arsenic a fluke of past until Gershman mentioned, successful passing during an interview, that successful summation to their enactment with the unicellular ciliate Stentor coeruleus, his laboratory was attempting to reproduce immoderate wacky worm experiments from the 1960s. Had I heard of them?

Gershman, I learned, was keen to prime up wherever McConnell had near off. As portion of a increasing cohort of cognitive scientists looking beyond the encephalon for clues to the origins and ground of memory, he’s fascinated by immoderate carnal that seems to retrieve without the payment of neural, synaptic networks. Little Stentor coeruleus, for example, tin modify its behavior based connected erstwhile experience—quite a feat for a single-celled carnal that can’t perchance person a neuron. Planarian worms, if McConnell’s findings were to beryllium believed, mightiness beryllium the adjacent large exemplary organism for memory research.

The occupation was, it wasn’t going well. In fact, nary substance however hard Gershman tried to bid them, nary of his planarians would larn a thing.

Can a worm learn? When McConnell posed the question successful the aboriginal 1950s, the conception that representation had thing to bash with synaptic associations betwixt neurons successful the encephalon was conscionable opening to summation currency. McConnell, past a postgraduate pupil successful science astatine the University of Texas, reasoned that planarians—among the simplest creatures with existent neurons—should truthful beryllium capable to learn.

His aboriginal worm experiments were not peculiarly novel. He simply substituted worms for rats successful what were, astatine the time, modular classical conditioning studies: repeatedly shocking the worms portion exposing them to a agleam light. After a play of this training, the worms came to subordinate the airy with the daze and scrunched their bodies successful anticipation whenever the airy flashed. Voilà: worm learning!

Planarians person alien features to connection for experiments. If a planarian is chopped successful half, some halves volition regrow into a caller worm—the process volition turn a caller head, and the caput volition turn a caller tail. A fragment arsenic tiny arsenic 1/279 of the archetypal worm tin regrow into a wholly mean big worm successful a substance of weeks, a regenerative capableness truthful almighty that, as 1 aboriginal naturalist enactment it, planarians are efficaciously “immortal nether the borderline of the knife.” For McConnell, this quality begged the question: When you chop a worm successful half, bash some halves remember?

This is wherever the existent worm torture began.

In the ’60s, McConnell, by past a young prof astatine the University of Michigan, started beheading his trained planarians. The worms that grew backmost from the severed heads behaved arsenic the originals had, associating the airy with the shock—a effect helium expected, fixed the preservation of their primitive brains. What amazed McConnell was that the worms that regenerated from headless tails remembered, too. This meant that immoderate signifier the worms’ memories took, they weren’t the exclusive purview of the brain. “It appeared that the memories were laid down passim the animal’s body,” McConnell aboriginal reflected.

Thrilled, McConnell pushed his experiments further. He chopped the worms into smaller and smaller pieces; each time, the regenerated segments retained the memory. He stitched the heads of trained worms onto untrained tails, but they kept falling off. He pureed trained worms and injected them into naïve recipients, a delicate process that the historiographer Larry Stern has compared to “impal[ing] a prune with a javelin.” Finally, remembering that immoderate planarians are cannibals, helium fed trained-worm puree to their brethren. In consequent trials, the “cannibal” worms picked up the airy effect close away, arsenic though they were remembering, alternatively than learning, what to do.

If McConnell’s experiments look gruesome, his enactment of enquiry was of his time. The find of the DNA helix successful the 1950s had revealed conscionable however overmuch accusation is packed into proteins and nucleic acids. The conception that the carnal traces of memories, oregon “engrams,” mightiness person immoderate chemic ground seemed plausible capable to galore scientists. Could McConnell’s cannibal worms person eaten an engram? McConnell surely thought so. He was convinced that their memories were encoded successful the operation of their RNA—and could beryllium transferred from worm to worm.

“In the jargon of machine engineering, accusation is ever ‘fed’ into a computer,” the writer Arthur Koestler aboriginal wrote successful an appreciative survey of McConnell’s work. “Here the metaphor became flesh.”

These were sensational findings, and McConnell took each vantage of the media attraction they generated. Before becoming a scientist, helium had had a little vocation successful radio, and helium knew however to repackage nuanced ideas arsenic pithy soundbites. In magazines specified arsenic Time and Esquire, helium spoke grandly of a aboriginal of memory consumption—of “piano acquisition pills” and “professor burgers.” He brought his trained worms onto The Steve Allen Show, and, belying his clean-cut hairsbreadth and horn-rimmed glasses, dubbed himself “McCannibal.”

Students began penning to McConnell’s laboratory astatine the University of Michigan to inquire for worm-training tips for their schoolhouse subject fairs, and McConnell shared advice. Science, helium believed, should beryllium for the people; helium saw himself arsenic a latter-day David pitching stones astatine organization Goliaths. This made him 1 of the astir celebrated nationalist scientists of his era, but it did not endear him to much superior peers. It besides didn’t assistance that helium published each his probe successful The Worm Runner’s Digest, a countercultural diary helium distributed from his lab.

The Worm Runner’s Digest was “sort of Mad Magazine meets a superior technological journal,” Gershman told maine recently. At its peak, it had immoderate 2,500 subscribers astir the world. The hand-drawn shield connected its screen featured a two-headed planarian and the Latin motto ignotum per ignotius, which astir translates to “the chartless explained done the adjacent much unknown.” Its 1959 inaugural contented consisted of lone 14 mimeographed pages astir the attraction and feeding of planarians, but it rapidly grew. In summation to publishing dozens of representation transportation papers and related scholarship, McConnell welcomed wit and printed science fabrication stories, rousing editorials, student-drawn planarian cartoons, spoof articles, and poems.

While the Digest is present thing of a cult classic, the premix proved confusing for galore readers. McConnell yet chopped the work successful half, not dissimilar a planarian worm, and renamed the superior fractional The Journal of Biological Psychology (no narration to the existent peer-reviewed diary Biological Psychology, founded successful 1973). But McConnell’s estimation arsenic a heretic and prankster was good established.

The wheels started to travel disconnected successful the mid-1960s. Although McConnell enjoyed a play of fame and funding—including an accelerated way to tenure astatine the University of Michigan—attempts to replicate his representation transfers yielded inconsistent results. While galore seemingly succeeded, the failures were much visible. In 1965, the Nobel Prize–winning biochemist Melvin Calvin tried to replicate McConnell’s worm experiments and failed, adjacent with the assistance of immoderate of McConnell’s erstwhile assistants and utilizing the aforesaid device. His high-profile work of the results sparked an acrimonious debate about, among different things, due worm handling.

By the 1970s, the planarian representation fad had travel and gone. Scientists had moved connected to rats, cats, goldfish, and adjacent praying mantises. Researchers showing palmy representation transfers successful rats—by injecting encephalon RNA from 1 carnal to another—had published their findings successful prestigious journals specified arsenic Nature and Science, making the planarian exemplary look unimpressive successful comparison. But erstwhile further experiments proved inconclusive, involvement successful the question of representation transportation petered out. As the subject historians Harry Collins and Trevor Pinch put it, “memory transportation was ne'er rather disproved; it conscionable ceased to inhabit the technological imagination.”

McConnell closed his laboratory successful 1971, and his agelong play of consequent obscurity was breached lone once, successful 1985, erstwhile helium became a unfortunate of the Unabomber. (He mislaid his proceeding temporarily aft the blast.) He died successful 1990. If a younger procreation of scientists is acquainted with his cannibal planarians, it’s arsenic “a cautionary communicative that neuroscientists archer to their students astatine bedtime to scare them distant from ill-fated projects,” Gershman said.

Still, McConnell’s unconventional enactment and contrarian cognition has lingered successful neuroscience lore, and the thought of memory transfer remains a taxable of backstage fascination. What if McConnell truly did negociate to provender a representation to a worm? For Gershman, who is searching for a mode to survey representation astatine a molecular level and link it to observable behavior, the question was an itch that had to beryllium scratched. He decided to settee the substance erstwhile and for all.

It each seemed straightforward enough. In the outpouring of 2025, Gershman and Maddie Snyder, 1 of his postdocs, acceptable retired to reproduce the worm-training protocol of 1 of McConnell’s students, Alan Jacobson. Jacobson’s papers were the astir rigorous of the planarian representation transportation era, and Gershman and Snyder followed them to the letter. “We wanted a behavioral ground to beryllium capable to survey the circuits that are driving representation successful these highly unstable animals,” Snyder said. “Are those circuits astatine each being utilized for representation consolidation oregon storage? Because if you suffer your caput and each those circuits are gone, past what is the mechanics of storing memory?”

Despite their champion efforts, however, they couldn’t bash what Jacobson, McConnell, and truthful galore others had done backmost successful the 1960s: information the worms to scrunch their bodies successful effect to light. (They reported the results connected biorxiv.org successful April 2026.) “I was truly scratching my caput astir this,” Gershman said. He’d assumed that the representation transportation would beryllium the dodgy portion of the experiment—not getting the worms to signifier a representation successful the archetypal place.

They talked to different planarian labs. They tried antithetic stimuli. They ran the planarian footage done a machine-learning pipeline. In desperation, Kelso and Snyder adjacent visited the Harvard Science Museum to analyse a vintage “inductorium,” an electric-shock contraption utilized successful midcentury worm science. But it offered nary clues.

Kelso searched for immoderate of McConnell’s erstwhile collaborators who mightiness inactive beryllium alive, and done a changeable of luck helium recovered interaction accusation for Daniel Kimble and his wife, Reeva, who had some worked successful McConnell’s lab. Now successful their nineties, they unrecorded successful Eugene, Oregon. When Kelso called them, helium discovered that not lone did they tally galore of McConnell’s experiments successful the 1960s, but they’d besides kept the full people archive of The Worm Runner’s Digest successful a container successful their basement.

Kelso and Snyder bought tickets to Eugene. Over the people of 2 days, portion consuming plates of homemade cookies and countless cups of tea, they absorbed everything they could from the Kimbles. On breaks from hand-scanning backmost issues of the Digest, they went stream-hopping adjacent and filled casserole dishes with silty caller water. Back astatine the Kimbles’ room table, the 2 generations of scientists watched the silt settee to spot what worms mightiness emerge.

This, aft all, is what McConnell did. Rather than utilizing laboratory strains of planarians, helium sourced his from a water adjacent the University of Michigan. And so, not wanting to permission immoderate chromatic unturned, Kelso made 1 last travel to McConnell’s erstwhile sportfishing grounds successful Michigan. He returned with integrative tubes full of worms, but not a azygous 1 was a learner. “At immoderate point, we had similar 12 antithetic strains of planaria, nary of which showed immoderate learning,” Gershman said.

As Snyder tells it, the Kimbles were perfectly convinced that their conditioning experiments successful the 1960s had worked. The worms learned—they were definite of it. The lit of the epoch seems to enactment their certainty; astatine slightest 36 labs reported akin results. So wherefore is it that erstwhile the nonstop aforesaid experiments are done today, utilizing the aforesaid laboratory protocol and adjacent the aforesaid worms, fished from the aforesaid Michigan waters, planarian worms are utterly uneducable?

One explanation, Snyder said, is that McConnell, the Kimbles, and each the different “worm runners” were inconsistent successful however they scored the planarians’ behaviour and whitethorn person misinterpreted much anodyne worm “turns” for the definitive “scrunch” of the airy reaction. Every idiosyncratic is simply a merchandise of their time, aft all, influenced successful myriad, often invisible ways by sociological conditions, backing pressures, and, successful this case, a highly charismatic leader. This mentation made Snyder hyperaware of her ain imaginable biases. “Throughout this full project,” she told me, “I was like, ‘What are the things that I americium taking for granted present successful our models of neuroscience, and our assumptions of what is known and unknown, that I should truly notice?’”

A much distant anticipation is that planarian worms themselves person someway changed implicit the past six decades—falling unfortunate to contamination oregon familial drift. Gershman finds this script unlikely. “What are the chances that a clump of researchers conscionable happened to bash these studies astatine the peculiar clip erstwhile this improvement happened?” helium asked, incredulous. “They conscionable got highly lucky, successful the millions of years of planarian evolution? And past our luck ran out?”

No substance the reason, successful 2026, contempt their tense strategy and elemental brains, planarians don’t learn. From an evolutionary perspective, this mightiness really marque sense. “The crushed that we larn associations, to immoderate degree, is truthful that we tin foretell information and debar it,” Snyder said. But planarians person a antithetic narration to danger. Their regenerative physiology, truthful cardinal to McConnell’s experiments, protects them from blunt trauma. Bitten successful half, they simply turn back. What usage is representation to specified a creature? “That’s a full different philosophical conundrum,” she said.

It’s a large clip to beryllium wrestling with specified conundrums. Planarian learning whitethorn beryllium a dormant end, but representation transportation experiments with different organisms are backmost successful technological vogue—and those experiments look to beryllium working. In 2018, the neuroscientist David Glanzman of the University of California, Los Angeles, performed a representation transplant connected the oversea slug Aplysia californica, a darling model organism for representation probe owing to its comparatively elemental tense strategy and gigantic neurons. After grooming the slugs to respond to a daze to their tails, Glanzman was capable to transportation the sensitization from 1 slug to different via a nonstop injection of genetic material. This suggested that immoderate facet of the representation was stored successful RNA, which was McConnell’s contention.

Then, successful 2021, the Princeton University geneticist Coleen Murphy recovered that Caenorhabditis elegans worms—microscopic roundworms with 302 neurons to their name—could larn to debar a pathogenic bacterium by eating, or adjacent conscionable swimming astir in, pureed worms who had learned the hard way. Murphy’s radical identified a retrotransposon, a jumping conception of familial material, called Cer1, that appears to “carry a memory” betwixt individuals, she said. A fewer years later, a radical astatine the Indian Institute of Science published a insubstantial suggesting that trained C. elegans worms merchandise extracellular vesicles—small lipid particles containing familial information—that can impart their training to their naïve counterparts.

None of these researchers are fractional arsenic flashy arsenic McConnell was, but their enactment indicates that helium whitethorn person been close astir worm representation aft all. He conscionable stake connected the incorrect benignant of worm—and doubled down connected it, contempt inconsistent evidence. In the end, helium mislaid his reputation, but his sheer gusto sparked the curiosity of different unconventional scientist. Fortunately, this one’s pursuing the evidence.

At Harvard, Gershman is shifting his absorption from the inscrutable planarian to the much legible C. elegans. It whitethorn not regenerate erstwhile it’s chopped successful half, but C. elegans is simply a long-standing exemplary organism in neuroscience—and it’s been consistently shown to learn. With caller experiments underway, Gershman is cautiously optimistic. “I conscionable anticipation we’re not going down different rabbit hole,” helium told me. A wormhole, connected the different hand—that’s for certain.

Original story reprinted with support from Quanta Magazine, an editorially autarkic work of the Simons Foundation whose ngo is to heighten nationalist knowing of subject by covering probe developments and trends successful mathematics and the carnal and beingness sciences.