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Bacteria and Your Brain

Gut flora affect brain function and might play important role in brain disorders.
If you count cells, we are not even close to being a majority human.

In our bodies, bacteria far outnumber human cells, 10:1 (link is external). The number of bacterial cells living inside the human body even exceeds the number of neurons in the brain (and that’s roughly 80 billion neurons).

Before you get disgusted at being a living Petri dish, realize that these bacteria are beneficial. They have a symbiotic relationship with our bodies, one that is vital to physical and mental health.

Recent research on the bacteria in our intestines, which is also called gut flora or microbiota, really makes a strong case that we should suspend judgment that what goes on in our intestines is gross. I am convinced that gut flora is actually awesome, and I’m going to talk about a few reasons why.

Gut flora plays an important role in digestion and health. All gut flora is not created equal, and recently the FDA has approved fecal microbiota transplants (link is external) to treat debilitating gastrointestinal conditions, such as hard-to-cure infections and autoimmune diseases like Crohn’s and colitis. (Mercifully, scientists are working on a pill that aims to do the same thing as a fecal transplant (link is external).)

But—and this is the awesome part—gut flora also affects how our brain works.

Cross-disciplinary research spanning neuroscience and gastroenterology (link is external) has started identifying the biological mechanisms behind the bidirectional connection between the gut and brain.

For example, scientists were able to make anxious mice non-anxious (link is external) by transplanting gut flora from non-anxious mice into the intestines of anxious mice. They were also able to do the reverse, making non-anxious mice anxious via fecal microbiota transplant, which is the same general procedure described above in humans.

And experiments in healthy humans show that just eating over-the-counter probiotic yogurt had widespread effects on the brain (link is external).

Published last week, a study in mice suggests a relationship between gut flora and some behaviors seen in autism spectrum disorder (link is external). This provocative study used an animal model of autism (link is external) to examine how different populations of gut flora affected the animals.
The mice used in the study had gastrointestinal problems that are seen in certain subpopulations of autistic humans, and the mice also displayed analogs of behaviors seen in some autistic humans.

The researchers treated the mice with probiotics, which altered their gut flora in a controlled way. The scientists then examined how probiotics changed both gastrointestinal malfunctions and behavior.

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