Researchers at UCLA have shown that gut microbes affect specific brain regions associated with processing sensory information in the body.[i] The study also shows that signals from the brain can inversely affect the composition of the gut microbes, in a two-way biochemical street.
Prior to this study, scientists had already established the following:
- In mice, gut bacteria is known to affect brain function and behavior.
- In mice, the brain is known to affect the composition of the gut bacteria.
- Studies have also shown an alteration in the gut bacteria in those with irritable bowel syndrome. However, there has been little consistency in just what those changes entail.
- Childhood trauma is associated with structural and functional brain changes, and is known to affect the gut microbiome. How these are related though, was unknown.
In this study, 29 adults with IBS and 23 healthy controls had their bacterial microbiota analyzed. Those with IBS fell into 2 distinct groups: one with bacteria similar to the control group. The second group, however, had altered gut bacteria and this latter group had a history of early life trauma. The two groups also showed differences in brain structure.
In terms of IBS, the thinking is that these “…alterations in the gut microbiota may feed back into sensory brain regions, altering the sensitivity to gut stimuli, a hallmark of people with IBS.”[ii]
What’s really interesting is that those with IBS whose gut microbiome was similar to the normal controls do not respond to microbiota treatments:
“Furthermore, consistent with clinical observations, the findings suggest the possibility that treatments aimed at altered gut microbial composition with antibiotics, probiotics, prebiotics, and certain diets may only work in subgroups of patients with an altered gut microbiome. Not only could such subgroups explain the lack of response to such treatments in a significant proportion of patients but also the worsening of IBS symptoms in subsets of patients with intake of food, fiber supplementation, and even probiotics. Identifying IBS subgroups based on gut microbiota, their related metabolomic profiles and corresponding brain signatures is likely to play an important role in optimizing therapies in IBS.”
You do have to wonder then, what is the cause of their IBS symptoms if their bacterial microbiome is normal? These researchers looked only at the bacterial microbiome. Is the virome ever involved in functional bowel problems? How about the mycobiome? We know that alterations in our native yeast populations is now associated with IBD, after all.
How, or if, these findings apply to other diseases remains to be seen. The researchers hypothesized that “Based on past clinical literature and brain regions altered in IBS, we expected to see a relationship between microbiota and emotion-related (amygdala, hippocampus) and sensory brain regions (basal ganglia, posterior insula, and primary sensory and motor regions).” Of course, these same regions are involved in many other illnesses. And functional bowel issues are also prevalent in other disorders, including autism, depression, anxiety disorders, schizophrenia, Parkinson’s, etc. – as are microbiome alterations.
There are still so many (I mean….SO MANY) unanswered questions here, but still, recognizing that early life external stimuli affect both the biome and the brain is an important first step.
[i] Labus, JS, et. al. Differences in gut microbial composition correlate with regional brain volumes in irritable bowel syndrome. Microbiome. 2017. 5:49.