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  • Adriano dos Santos

Gut Influences Brain and Behavior

You already know your gut and brain communicate. How else to explain the sudden onset of gut troubles when you get some bad news or you realize your wallet is missing?

Scientists have been studying this “gut-brain axis” for decades. They know that the digestive tract (including the gut-based centeric nervous system) and the brain (part of the central nervous system) send messages back and forth constantly. What’s new about this gut-brain connection in recent years, however, is information about the role of the gut microorganisms in this two-way communication channel.

How much can behavior really be controlled by microbes? So far the evidence comes mainly from germ-free mice. Studies have shown the presence or absence of certain microbes can, in effect, change a mouse’s personality— how often it takes risks, how much it explores, and what it does in a challenging situation. But, of course, humans are a little more behaviorally complex than mice.

New evidence shows gut microbes can indeed play a role in the way the brain functions in humans. Some of this evidence comes from studies that show how antibiotics and probiotics, which target the gut, can affect the brain. Here are some examples:

Antibiotics: Doctors have reported cases of people who receive a course of antibiotics and experience a drastic behavior change; this condition, called “antibiotic-induced psychosis,” goes away when the antibiotics are stopped. It is well known that antibiotics can drastically change the microbiome.

Probiotics: A recent study found women who consumed a probiotic fermented milk (via functional magnetic resonance imaging, or fMRI) showed differences of activity in the regions of their brains that processed emotions and sensations.

Of course, we’d like to know how to control a huge range of human behaviors—from anxiety-induced nail biting, to eating an entire box of cookies, or even the repetitive movements made by children with autism. In the future, modulating the gut microbiome, with the help of wellness services like those provided by Viome, will be one way to help us control these unwanted behaviors.

Interventional studies in this area are difficult, however, because scientists can’t ethically carry out experiments where they try to manipulate the behavior of humans. More data need to be collected on how gut microbiota correlate with individual emotions, behaviors, and personality traits in people’s everyday lives. Then, the data might get scientists closer to knowing how adding or removing particular species of intestinal microbes could influence brain function or behavior.

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