Image: Ana M Valdes, et. al., Role of the gut microbiota in nutrition and health. Science and Politics of Nutrition, June 13, 2018
Everyone has a huge number of bacteria, fungi and viruses in their guts. A lot of these microbes live in a part of the large intestine called the cecum. But the total human microbiome—the thriving, ever-evolving colony of microorganisms in and on our bodies—spreads almost everywhere.
And they may be controlling your feelings, thoughts and actions.
I'm not talking about an indirect connection, for example, not feeling good because your digestive tract is upset. Your microbiome can directly influence your emotions by stimulating the release of brain chemicals—in your gut.
Neurochemicals—the chemicals secreted in your brain—cause changes in our emotions by causing changes in our bodies. Oxytocin, for example, is known as the cuddle chemical. It creates feelings of warmth, trust and love towards others. (For a full discussion of how this works, read my book The Chemistry of Connection: How the Oxytocin Response Can Help You Find Trust, Intimacy and Love.)
Briefly, our brains secrete oxytocin when we have a positive social interaction. It makes us feel more open and trusting. This feeling of openness also influences our thoughts. When I get that oxytocin feeling, I may say to myself, "Wow, Carlos is a good person."
Here's the amazing thing: Gut microbes can produce hormones and neurotransmitters that are identical to those produced by humans, including oxytocin and serotonin, two chemicals that play a big role in mood.
Studies of mice have shown that microbes stimulate the production of oxytocin in their guts. A paper by Susan Erdman of MIT concludes, "Microbial reprogramming of host oxytocin may offer far-reaching benefits in physical, mental, and social health for healthful longevity."
A UCLA study of healthy women brought this into the human realm. It divided the women into two groups based on the prevalence of two different bacteria. Researchers found differences in their brain structures. One group had more of the brain structures responsible for processing of information and memory. The other group had more connections between the parts of the brain involved in processing emotions and sensory information.
Microbes and your behavior
The parasitic microbe Toxoplasma gondii does something very weird to mice: It makes them lose their fear of cats—permanently.
It can change human behavior, too, making people more likely to engage in risky behavior.
People infected with t. gondii have a 2.65 times higher risk of traffic accidents have traffic accidents. Another study of infected men and women found that the men were more likely to disregard rules and were more expedient, suspicious, jealous, and dogmatic. Infected women, on the other hand, were more warm-hearted, outgoing, conscientious, persistent, and moralistic.
What other bugs in your belly might have similar effects on your feelings, thoughts and behavior? Science doesn't know. But there are more than 800 clinical trials underway investigating how gut microbes can be used to treat disease.
Microbe mind control
It's clear that the gut microbiome affects us in all sorts of ways. Altering the composition of the teeming hordes in the intestine could change you profoundly. Could this be used for evil?
My next novel, book two in the Finder series, concerns a plot to do just that.