FINDINGS

Researchers have identified gut microbiota that interact with brain regions associated with mood and behavior. This may be the first time that behavioral and neurobiological differences associated with microbial composition in healthy humans have been identified. BACKGROUND

Brain-gut-microbiota interactions may play an important role in human health and behavior. Previous research suggests 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. There is, however, little evidence of this in humans.

For this study the researchers sought to identify brain and behavioral characteristics of healthy women clustered by gut microbiota profiles. METHOD

Forty women supplied fecal samples for profiling, and magnetic resonance images were taken of their brains as they viewed images of individuals, activities or things that evoked emotional responses. 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. The Bacteroides group showed greater thickness of the gray matter in the frontal cortex and insula, brain regions involved with complex processing of information. They also had larger volumes of the hippocampus, a region involved in memory processing. The Prevotella group, by contrast, showed more connections between emotional, attentional and sensory brain regions and lower brain volumes in several regions, such as the hippocampus. This group's hippocampus was less active while the women were viewing 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 Bacteroides group. IMPACT

These results support the concept of brain-gut-microbiota interactions in healthy humans. Researchers do not yet know whether 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. Both possibilities, however, could lead to important changes in how one thinks about human emotions.

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AUTHORS

The authors of the study are Dr. Kirsten Tillisch, Dr. Emeran Mayer, Arpana Gupta, Zafar Gill and Jennifer Labus of UCLA; Rémi Brazeilles, Boris Le Nevé and Muriel Derrien of Danone Research in France; Johan E.T. van Hylckama Vlieg of Microbiome and Human Health Innovation in Denmark; and Denis Guyonnet of Symrise Group in France. Tillisch is also associated with the VA Greater Los Angeles Healthcare System. JOURNAL

This study was published by the peer-reviewed journal Psychosomatic Medicine: Journal of Behavioral Medicine. FUNDING

This research was supported by grants from Danone Research and from the National Institutes of Health, including R01 DK048351, P50 DK64539, P30 DK041301 and R01 HD076756. In addition, pilot funds were provided for brain scanning by the Ahmanson-Lovelace Brain Mapping Center. DISCLOSURE

Tillisch received funding from Danone Research. Mayer is on the advisory boards for yogurt product company Dannon and its parent company Danone. Derrien, Le Nevé, Guyonnet and Brazeilles are or were employed by Danone Research at the time of the study. The remaining authors disclose no conflicts.