The Gut Microbiome in the Regulation of Mood

            On April 7^th, 2020, Dr. Sam Sisodia from the University of Chicago demonstrated that long term antibiotic treatment in mice resulted in a reduction in the formation of Ab amyloidosis, suggesting that the gut microbiome may play a role in the formation of some neuropathologies. His lecture inspired me to do some further research into the relationship and interactions between the gut microbiome and the brain, a system that is specifically called the gut-brain axis. Although the gut-brain axis had already been studied long before this area of research gained new traction, it has since become a great interest to scientists with the characterization of the gut microbiome about a decade ago.

            It is well known that the gut microbiome plays an essential role in gastrointestinal health. However, because of its bidirectional communication with the brain, it has been discovered that the gut microbiome plays an important role in the regulation of behaviors and cognitive functions such as emotions and moods. For instance, the gut microbiome has been found to be able to influence the myelination of axons in the frontal lobes of mice, and mice who ingested probiotics saw reduced anxiety and depression-like behaviors. Many of these findings are based on animal models, and there are limited studies on the human gut-brain axis. The human studies that do exist only focus on self-reported data, so no solid conclusions about human gut microbiome’s impact on human behavior can be drawn from these studies.

To address this, a scientific study titled “Probiotics drive gut microbiome triggering emotional brain signatures” by Bagga et. al 2018 attempted to replicate animal evidence for gut microbiome influence on cognitive and emotional behavior in humans. They specifically investigated whether the ingestion of probiotics would produce any measurable cognitive changes, measured via behavioral and cognitive tasks and fMRI scans, in healthy human volunteers. In a double-blind study with three experimental groups [a probiotic (PRP) group, which took a multi-strain probiotic for 4 weeks, a placebo (PLP) group, which took a placebo for 4 weeks, and a control (NI – no intervention) group, which did not take a placebo or the probiotic], the authors carried out pre- and post-experiment fMRI sessions and surveyed volunteers on their mood. They also took some stool samples from the PLP and PRP group for microbial analysis.

The study was able to provide ample, multi-dimensional evidence that the administration of probiotics does have a significant effect on brain areas involved in emotion and memory. First, questionnaires revealed that the PRP group reported a significant increase in positive changes in their mental health and a decrease in depression-like symptoms like hopeless and risk aversion. This suggests that probiotic administration influenced participants’ overall mood and improved participant general well-being. Moreover, fMRI scans found increased activation in brain regions like the anterior cingulate, the precuneus, the parahippocampal gyrus, which are all areas that mediate and interact with areas involved in emotional, decision-making, and memory processes, in the PRP group. It was also found that the gut microbiome of the PRP group had slight but significant changes in microbial community composition, and these changes were found to be significantly correlated to behavioral measures. Given all of the substantial evidence, I found it safe to conclude that the authors had accomplished what they had set out to do. Indeed, it appears that the gut microbiota does influence and regulate human cognitive and emotional behaviors.

These exciting findings are one of the many discoveries being made about the underlying mechanisms of the gut-brain axis interactions. As demonstrated by this study, the gut microbiome plays some role in regulating our mood and emotions. Future studies into this area of research will give precious insight into the complex world living in our gastrointestinal tract and help further understand and improve overall human gastrointestinal and cognitive health.

References

Bagga, Deepika, Johanna Louise Reichert, Karl Koschutnig, Christoph Stefan Aigner, Peter Holzer, Kaisa Koskinen, Christine Moissl-Eichinger, and Veronika Schöpf. 2018. “Probiotics Drive Gut Microbiome Triggering Emotional Brain Signatures.” Gut Microbes 9 (6): 486–96. https://doi.org/10.1080/19490976.2018.1460015.