Think again: Science explores link between gut and mind

Cat feces can transmit the parasite Toxoplasma gondii. According to the Centers for Disease Control, at least 40 million Americans are infected with the parasite, though many suffer no physical symptoms. Pexels

We humans fancy ourselves the masters of our own destiny, or at the very least, feel that we make choices of our own free will. The idea that someone or something might be able to control our thoughts and actions is terrifying. We desperately hope that “mind control” is limited to Jedi mind tricks in Star Wars, or mass brainwashing in The Manchurian Candidate; pure fiction. Yet the clichéd phrase “the devil made me do it” suggests that from time to time, we might fall victim to outside influences.

Well, real-life research has shown that if we act against our better judgement, the cat might be to blame. Even more bizarre is the fact that, beyond a doubt, our intestinal bacteria can strongly influence our emotions and behavior. That’s right; it could be that faulty feces are at fault. And for insects, their excuse is “a fungus made me do it.”

Toxoplasmosis is a common infection caused by a single-cell parasite associated with cats, Toxoplasma gondii. Able to infect most warm-blooded animals, it requires a cat — domestic or wild — to complete its life cycle. According to the U.S. Centers for Disease Control, at least 40 million Americans are infected with T. gondii, the vast majority of whom have no physical symptoms.

Across the world, about one-third of humanity carries the parasite. Infections typically result from contact with cat feces and sometimes cause a temporary low-grade fever, headache, or swollen lymph tissue in the neck. For healthy adults, there is little risk, but pregnant women and those on immunosuppressant drugs can develop complications.

You may have read how rodents infected with T. gondii lose all fear of cats due to the effect the pathogen has on their nervous system. In fact, a 2011 Stanford University study proved that infected rats actually become sexually aroused by the smell of cat urine, and seek it out. While that’s creepy, it’s old news.

The really big development is the medical community’s finding that when young children contract Toxoplasma gondii, they are at increased risk of mental-health issues as teens or young adults. Studies done over the past decade have shown a link between T. gondii infections and mental-health issues such as schizophrenia, depression, aggressive behavior and impaired cognition.

Research published in August 2014 in the Journal of Nervous and Mental Disease found a very strong correlation between the presence of T. gondii and such conditions, but the authors stopped short of calling them a direct result of toxoplasmosis.

And now let’s talk about gut feelings. As you may have heard, most of the cells within the human body are not human: about 57% belong to microbes, and 43% are “us.” Kind of spooky, I know. Apparently it’s important to have many different species of gut bacteria, and lots of them.

In places like Ireland, Australia, Belgium, the U.S. and Canada, medical researchers are performing what is called “fecal material transplants” or FMTs. During an FMT, fecal matter from donors who have a healthy, diverse microbial community is placed in patients who lack such diversity. The results have been astounding: conditions such as Parkinson’s, obesity and, especially, depression improve dramatically.

In a BBC report published in April 2018, neuroscientist Dr. Ted Dinan of University Hospital in Cork, Ireland, said: “If you compare somebody who is clinically depressed with someone who is healthy, there is a narrowing in the diversity of the microbiota. I’m not suggesting it is the sole cause of depression, but I do believe for many individuals it does play a role in the genesis of depression.”

Researchers have gone the other way and transplanted fecal material from depressed humans into animals, thereby inducing clinical depression in the test subjects.

And there is a fungus among us (actually several fungi, but that is not as fun to say) that turns insects into mushroom zombies. In 2018, Cornell University researchers discovered that a native fungus, Batkoa major, and possibly other species in the Batkoa genus, had killed off a large number of spotted lanternflies, invasive bugs which pose a serious threat to vineyards, orchards, and forests.

It seems that when an insect comes in contact with Batkoa spores, they enter its body through leg joints or other chinks in its armor, and start to multiply. As the fungi begin to overwhelm the insect, it stops eating, mating or anything else fun, and crawls to a high exposed place like a tree trunk or the tip of a tall grass blade. There the fungus sends out threadlike hyphae from within the bug, essentially “sewing” the insect to its perch.

Nearly done with its macabre choreography, the Batkoa fungus somehow triggers the lanternfly to open its wings fully, exposing its soft abdomen completely. That is the last time the bug moves. Finally, Batkoa spores explode (well, gently) from the insect’s belly, showering everything below with powdered death.

This is nothing new. A paper published in the journal Fungal Biology on June 5 details how Oregon State University researchers found a 50-million-year old ant preserved in amber with a parasitic mushroom sprouting from its anus like an umbrella. I don’t know about you, but toxoplasmosis sounds like a picnic compared to a brain-hijacking fungus that controls your limbs, has you climb a tall structure and latch on, then kills you and launches a spore-laden parasol from your butt. Thank goodness I’m still in control. Once I finish that “honey-do” chore list, that is.

Paul Hetzler is a former Cornell Cooperative Extension educator.

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