Neural Hijacking: Your Brain On T. gondii

Popular zombie fiction often blames the shambling hordes on an infection that alters brain function. In this case, fact has fiction beat: the T. gondii microbe hijacks human brains already.


| October 2014



Zombie man

A T. gondii infection may not make you look like this—but it does alter your brain chemistry in some startling ways.

Photo by Fotolia/nito

Timothy Verstynen and Bradley Voytek take on the neuroscience of the zombie brain in Do Zombies Dream of Undead Sheep? (Princeton University Press, 2014) with witty analyses of the characteristic lumbering gait, insatiable hunger for brains and memory-less existence of the undead. Through this exploration they shed light on fundamental neuroscientific questions while bringing in examples from zombie popular culture. The following excerpt from Chapter 11, “Fighting the Zombie Apocalypse…With Science!” offers an example of a microbe that can hijack human brains.

An Overview of T. gondii

Humans have a long history of having their brains manipulated by parasitic organisms.

It turns out that cat poop can hijack your brain. Well, not the poop per se, but a tiny little organism that lives there: Toxoplasma gondii. T. gondii is a single-cell organism that has an interesting life cycle. It all starts when two microbes really like each other and undergo sexual reproduction. Apparently, the only place that the T. gondii organism can “get in the mood” happens to be the intestinal lining of cats.

As can happen in a microscopic love story, eventually new little microbes are born and go out into the world with the rest of the things in the intestinal tract. In this case they’re packaged in little cysts that can survive in the brutal world outside the gut. The hope is that another cat will step in the poop and the little cyst will make its way up to the cat’s mouth when the cat is eating, and from there, it’s back to the gut for more love making.

Now here is where the T. gondii life cycle gets more interesting. What happens if the cyst is ingested by an animal other than a cat? Rather than just live out a celibate life without reproducing, the T. gondii microbe goes in for self-love and starts reproducing asexually (i.e., cloning). This can give the host animal a flu-like illness as the infection grows, producing a fairly harmless condition called toxoplasmosis. Usually the symptoms pass and the infected animal (human or otherwise) appears to recover fully (though we have to note that toxoplasmosis is quite dangerous to human fetuses, which is why pregnant women are advised not to take care of the litter box or otherwise be in contact with cat feces).

At least it seems like the person or animal recovers.