Interactions between gut bacteria and the brain may play an important role in human health and behavior.
In a new study, researchers at the University of California, Los Angeles have discovered that microbiota in the gut interacts with brain regions associated with mood and behavior in healthy humans. The findings add to the growing body of evidence of a significant link between the gut and the brain.
Earlier studies have shown that microbiota, a community of microorganisms in the gut, can influence behavior and emotion. Rodent models have demonstrated the effects of gut microbiota on emotional and social behaviors, such as anxiety and depression, but there has been little scientific evidence in humans.
For the new study, the researchers wanted to identify brain and behavioral characteristics of healthy women clustered by gut microbiota profiles. A total of 40 women gave fecal samples for profiling, and magnetic resonance images were taken of their brains as they looked at images of individuals, activities, or other objects that evoked an emotional response.
The women were divided by their gut bacteria composition into two groups: 33 had more of a bacterium called Bacteroides; the remaining seven had more of the Prevotella bacteria.
Women in the Bacteroides group showed greater thickness of the gray matter in the frontal cortex and insula, brain regions involved with complex processing of information. These women also had larger volumes of the hippocampus, a region involved in memory processing.
In contrast, women in the Prevotella group displayed more connections between emotional, attentional and sensory brain regions and lower brain volumes in several regions, such as the hippocampus.
In this group, the women’s hippocampus was less active as they looked at negative images. They also rated higher levels of negative feelings such as anxiety, distress and irritability after looking at photos with negative images than did the women in the Bacteroides group.
The new findings support the concept of brain-gut-microbiota interactions in healthy humans. Researchers still do not fully understand whether the bacteria in the gut influence the development of the brain and its activity when unpleasant emotional content is encountered, or if existing differences in the brain influence the type of bacteria that reside in the gut.
In either case, however, the findings could lead to important changes in how we perceive human emotions.