What part of the brain controls zombies?
How the Zombie Fungus Takes Over Ants’ Bodies to Control Their Minds
The infamous parasite’s methods are more complex and more sinister than anyone suspected.
November 14, 2017
To find the world’s most sinister examples of mind control, don’t look to science fiction. Instead, go to a tropical country like Brazil, and venture deep into the jungle. Find a leaf that’s hanging almost exactly 25 centimeters above the forest floor, no more and no less. Now look underneath it. If you’re in luck, you might find an ant clinging to the leaf’s central vein, jaws clamped tight for dear life. But this ant’s life is already over. And its body belongs to Ophiocordyceps unilateralis, the zombie-ant fungus.
When the fungus infects a carpenter ant, it grows through the insect’s body, draining it of nutrients and hijacking its mind. Over the course of a week, it compels the ant to leave the safety of its nest and ascend a nearby plant stem. It stops the ant at a height of 25 centimeters—a zone with precisely the right temperature and humidity for the fungus to grow. It forces the ant to permanently lock its mandibles around a leaf. Eventually, it sends a long stalk through the ant’s head, growing into a bulbous capsule full of spores. And because the ant typically climbs a leaf that overhangs its colony’s foraging trails, the fungal spores rain down onto its sisters below, zombifying them in turn.
The fungus’s skill at colonizing ants is surpassed only by its skill at colonizing popular culture. It’s the organism behind the monsters of the video game The Last of Us and the zombies of the book The Girl With All the Gifts. It’s also an obsession of one David Hughes, an entomologist at Pennsylvania State University, who has been studying it for years. He wants to know exactly how this puppet master controls its puppets—and his latest experiments suggest that it’s even more ghoulish than it first appears.
Hughes’s student Maridel Fredericksen used a special microscope to julienne infected ants into slices that were just 50 nanometers thick—a thousandth of the width of a human hair. She scanned each slice, compiled the images into a three-dimensional model, and painstakingly annotated which bits were ant and which bits were fungus. It took three months to mark up just one muscle. To speed things up, Hughes teamed up with computer scientist Danny Chen, who trained an artificial intelligence to distinguish ant from fungus.
“Something much more intricate must be going on.”
When the fungus first enters its host, it exists as single cells that float around the ant’s bloodstream, budding off new copies of themselves. But at some point, as Fredericksen’s images show, these single cells start working together. They connect to each other by building short tubes, a kind that have only ever been seen before in fungi that infect plants. Hooked up in this way, they can communicate and exchange nutrients.
They can also start invading the ant’s muscles, either by penetrating the muscle cells themselves or growing into the spaces between them. The result is what you can see in this video: a red muscle fiber, encircled and drained by a network of interconnected yellow fungal cells. This is something unique to Ophiocordyceps. Hughes’s team found that another parasitic fungus, which fatally infects ants but doesn’t manipulate their minds, also spreads into muscles but doesn’t form tubes between individual cells, and doesn’t wire itself into large networks.
Whenever Hughes or anyone else discusses the zombie-ant fungus, they always talk about it as a single entity, which corrupts and subverts a host. But you could also think of the fungus as a colony, much like the ants it targets. Individual microscopic cells begin life alone but eventually come to cooperate, fusing into a superorganism. Together, these brainless cells can commandeer the brain of a much larger creature.
But surprisingly, they can do that without ever physically touching the brain itself. Hughes’s team found that fungal cells infiltrate the ant’s entire body, including its head, but they leave its brain untouched. There are other parasites that manipulate their hosts without destroying their brains, says Kelly Weinersmith, from Rice University. For example, one flatworm forms a carpetlike layer over the brain of the California killifish, leaving the brain intact while forcing the fish to behave erratically and draw the attention of birds—the flatworm’s next host. “But manipulation of ants by Ophiocordyceps is so exquisitely precise that it is perhaps surprising that the fungus doesn’t invade the brain of its host,” Weinersmith says.
In retrospect, that makes sense. “If such parasites were merely invading and destroying neuronal tissue, I don’t think the manipulated behaviors that we observe would be as compelling as they are,” says Charissa de Bekker, from the University of Central Florida. “Something much more intricate must be going on.” She notes that the fungus secretes a wide range of chemicals that could influence the brain from afar.
So what we have here is a hostile takeover of a uniquely malevolent kind. Enemy forces invading a host’s body and using that body like a walkie-talkie to communicate with each other and influence the brain from afar. Hughes thinks the fungus might also exert more direct control over the ant’s muscles, literally controlling them “as a puppeteer controls as a marionette doll.” Once an infection is underway, he says, the neurons in the ant’s body—the ones that give its brain control over its muscles—start to die. Hughes suspects that the fungus takes over. It effectively cuts the ant’s limbs off from its brain and inserts itself in place, releasing chemicals that force the muscles there to contract. If this is right, then the ant ends its life as a prisoner in its own body. Its brain is still in the driver’s seat, but the fungus has the wheel.
Zombie neuroscience: Inside the brains of the walking dead
The rotting flesh, the shuffling walk, the unintelligible groans — it’s not hard to spot a zombie at a glance even among the most gruesome of Halloween monsters. But what’s going on inside their brain?
Based on fictional accounts of the undead creatures’ bizarre behavior, several prominent scientists have taken a crack at the mystery. Neuroscientists Bradley Voytek of the University of California, San Diego, and Tim Verstynen of Carnegie Mellon University are both avid zombie fans. Back when they were in graduate school together, they would sit around watching zombie movies and got to thinking about what causes zombies to behave as they do.
«We mocked up what a zombie brain would look like,» Voytek said, and «it kind of took off.» Voytek calls it a way of getting people to accidentally learn something about the brain. [Zombie Facts: Real and Imagined (Infographic)]
Diagnosing a zombie
Broadly speaking, zombies can be either slow zombies (think the original «Dawn of the Dead») or fast zombies (à la the film’s 2004 remake). Slow zombies shuffle in an uncoordinated manner and can’t open doors, suggesting a problem with the cerebellum, Voytek said. This region at the back of the head, known as the «little brain,» plays an important role in coordinated movements. Tasks such as picking up a quarter on the ground are actually really hard, Voytek said. «We still can’t get robots to do this.»
All zombies — fast ones included — seem to have poor memory and lack the ability to plan as a group.
«They don’t really have any social skills,» Voytek said.
They also lack cognitive control — there’s no delaying the gratification of warm human flesh. These symptoms suggest their frontal lobes probably aren’t functioning correctly, Voytek said. In animal studies, cutting connections to the frontal lobes causes lots of problems, he added.
Then there’s the matter of zombie communication, or lack thereof. Voytek and Verstynen made an educational video in which they «diagnosed» zombies with a condition called Wernicke’s aphasia, which results from damage to a bundle of connections between the brain’s temporal and parietal lobes. Of course, brain damage is not a joking matter, Voytek said, but he finds it interesting to think about. [The 9 Most Bizarre Medical Conditions]
Zombies may have impaired brain function in many ways, but they do have a razor-sharp sense of smell — at least when it comes to sniffing out living human flesh. In a scene from the movie and comic book «Walking Dead,» the protagonists smear themselves with the organs of dead zombies to prevent «live» zombies from smelling them.
By comparison, healthy humans are thought to have a poor sense of smell. But studies have shown that people can track scents really well if they focus on the task, Voytek said. In one study, blindfolded undergraduates at the University of California, Berkeley, were able to track a streak of chocolate in the grass by smell alone, and did it surprisingly well. So the zombie’s ability to tell healthy bodies from decaying ones (i.e. other zombies) is «certainly plausible,» Voytek said.
All of these theories about zombie neuroscience are idle speculation. But could zombies exist in real life? The concept of zombies has its roots in Haitian lore, in which voodou (or voodoo) priests create a powdery substance that allegedly turns people into zombies. A component of this powder is a nerve toxin from pufferfish capable of keeping people in a state of suspended animation. Haiti has actually banned the practice of making these human zombies.
The animal world has its own share of zombie stories. A fungus that infects carpenter ants causes the insect to climb underneath tree leaves and die. The fungus sprouts a stalk from the zombie ant’s head, sending out a shower of spores to infect other ants.
Wasps are known to inject their venom into cockroaches, paralyzing but not killing them. The wasp drags the helpless roach to its nest and lays its eggs inside the bug’s abdomen. When the baby wasps hatch out, they eat the cockroach alive from the inside out.
And, of course, there’s the Toxoplasma gondii parasite, which can infect humans. In rats, the parasite makes rodents stop fearing the smell of cat urine, which usually proves fatal for the rats. In pregnant women, toxoplasma infection can cause congenital problems such as deafness or mental retardation in the baby.
But when it comes to flesh-eating, shuffling monsters, the zombie phenomenon remains firmly rooted in fiction.
«No kind of brain damage could make anything like a zombie happen,» Voytek said.
Follow Tanya Lewis on Twitter and Google+. Follow us @livescience, Facebook and Google+. Original article on LiveScience.
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The zombie fungus from ‘The Last Of Us’ is real — but not nearly as deadly
In the video game and HBO show The Last of Us, an infectious fungi turns humans into zombies.
David McNew/Getty Images
In the video game and HBO show The Last of Us, humans struggle to survive after an infectious fungus turns ordinary people into zombies. Creators of the franchise didn’t look far for inspiration — the series is based off a real-life species of fungus that performs a kind of «mind control» on its insect hosts.
Ophiocordyceps unilateralis, otherwise known as cordyceps or zombie-ant fungus, infects insects such as ants or spiders. Like other parasites, cordyceps drains its host completely of nutrients before filling its body with spores that will let the fungus reproduce. It then compels the insect to seek height and remain there before it expels these spores, infecting other nearby insects in the process.
The Zombies That Walk Among Us
Bryn Dentinger, a biology professor at the University of Utah and curator of mycology at the Natural History Museum of Utah, told NPR that the fungus is one of the best known, and probably most commonly encountered, kinds of organisms with this mind control capability.
And he said that scientists aren’t entirely sure how cordyceps is able to have the effect that it does on insects, although there are theories.
«There seems to be some combination of physical manipulation of muscle fibers, for example, possibly growth into the brain itself, that can impact its behavior,» he said. «But there’s also very likely some sort of chemical attack on the host, either small molecules, or proteins or some other things, that end up manipulating brain behavior.»
Dentinger, who is also a fan of HBO’s adaptation of The Last of Us, said that there are some major differences between how the fungus is portrayed in the show and in real life. Cordyceps does not typically infect other hosts through the mouth, for example, and the infected aren’t connected to one another through a network.
And, perhaps the most important: The fungus cannot infect humans.
«Our body temperatures are high enough that most organisms, their proteins would denature at that temperature and so they can’t survive in our bodies,» he said.
‘Zombie’ Ants And The Fungus That Saves Them
But there are species of fungus that are able to withstand higher temperatures, and can therefore infect humans. Climate change, as Dentinger explains, is equipping certain fungi with the capacity to withstand higher temperatures.
And it’s possible that a fungus with similar mind-control capabilities could, at some point, be able to withstand a human’s body temperature.
«That may be one reason why we’re seeing more fungal infections in human humans, but again, to date, none of them are cordyceps,» he said. «However, maybe that will happen in the future, but, at the moment, that is not a possibility.»
And, as Dentinger, there are already species of fungus that alter a human’s mental processing, such as psilocybin, otherwise known as «magic mushrooms.» Meanwhile, other kinds of fungi are already ubiquitous in human life. Take yeast, for example, which is found in bread and in the human gut.
And while the prospect of fungus being able to manipulate human behavior isn’t impossible, it’s not likely, according to Dentinger. The traits the fungus have that allow them to attack an insect host are very specific to that insect — and it’s not easily transferable to another species.
«It’s unlikely that they would be able to hop from, say, an ant to a human, because we’re so different,» he said.