It is becoming widely known that gut bacteria influence much more than our digestive process. The bacteria living in the digestive system impact our general health. Furthermore, scientists are now discovering that this influence goes beyond physical health. A study out of the University of California Los Angeles (UCLA) discovered evidence that gut microbes affect our emotions. Specifically, they impact how we respond to fear.

Study Proves Brain and Gut Microbe Interactions

In their study, UCLA researchers examined fecal samples of 40 women to identify their gut microbiome. In addition, these women were hooked up to an MRI scanner and then shown images designed to provoke an emotional response. The study identified two types of gut bacteria that potentially impact the brain areas associated with mood and general behavior.

First, the scientists found Prevotella to be common in seven of the women. "The Prevotella group showed less hippocampal activity viewing negative valences images." The hippocampus regulates emotions, consciousness and memories. Women in this first group had profoundly negative emotions associated with distress and anxiety when viewing negative images.

On the other hand, Bacterioids were prevalent in the other 33 women. In the imaging analysis, "the Bacteroides cluster showed greater prominence in the cerebellum, frontal regions, and the hippocampus." We associate the frontal regions of the brain with problem-solving and more complex processing. The results showed that women in this group were less emotional when viewing undesirable images.

Consequently, MRI imaging in this study shows that certain gut bacteria influence the physical structure of the brain. The researchers believe their study supports the concept of brain-gut-microbe interactions in healthy humans.

Gut Bacteria Finds Ways to Bypass Blood-Brain Barrier

This is not the first time that scientists have identified a link between the gut and the brain. Throughout the last decade, researchers have been exploring the effects that gut microbes have on our emotions and neural chemistry.

Neuroscientist John Cryan was involved in such research at the University College Cork, in Ireland. He discovered that even though the brain is anatomically isolated from the digestive system, interactions still exist. Moreover, this "communication" happens regardless of the blood-brain barrier, which protects the brain from pathogens.
Cryan's study added to the growing evidence that signals from beneficial bacteria nonetheless find a way through the barrier. Somehow - though his 2011 paper could not pinpoint exactly how - micro-organisms in the gut tickle a sensory nerve ending in the fingerlike protrusion lining the intestine and carry that electrical impulse up the vagus nerve and into the deep-brain structures thought to be responsible for elemental emotions like anxiety. (source)
In brief, neuroscience continues to confirm that a connection between the brain and gut bacteria exists. Although we don't yet know the specifics, it's safe to say that a healthy gut may help balance mood and affects how we respond to emotional situations.