Brain Microbiome: Intestinal Bacteria in the Human Brain

The discovery is fascinating and intimidating. Bacteria have been discovered, but there is no explanation of how they have reached the brain, nor is it known if they are beneficial or harmful. It is even suspected that they can influence the mood and very possibly the personality of each individual.


So far we have had very interesting news about the relationship of the gut microbiota and the brain, but it seems that the relationship is much more intimate than was suspected at first. At the last conference of the Society of Neuroscience, the University of Alabama has presented a report that shows how some intestinal bacteria inhabit different regions of the brain, which seems to be a brain microbiome.

This discovery is both fascinating and intimidating. The bacteria have been found, they are known to be there, but there is still no explanation as to how they have reached the brain, or whether they are beneficial or harmful. It is intuited, even, that they can influence the mood and perhaps, the personality. Let’s deepen.

What is the gut microbiome?

The gut microbiome is the set of microorganisms that live in our intestines, approximately one hundred trillion thousand different species of bacteria, which, in turn, are made up of more than three million genes. Of all of them, only one third is common to all human beings, the rest are exclusive to each person. So the gut microbiome is an important part of the identity of each one of us.

Among its most important functions we can highlight the regulation of the immune system, the absorption of nutrients and the control of external pathogens. Any alteration in the intestinal microbiota can be the origin of autoimmune diseases, allergies and infections. In fact, it has also been linked to Alzheimer’s and Parkinson’s, recently.

On the other hand, imbalances in this intestinal floral generate endotoxins, high levels of oxidation, and the accumulation of abdominal fat. In addition, chronic inflammation causes cardiovascular problems and diabetes.

Although there is widespread fear of microbes and bacteria, the truth is that we can not live without them. We are not aware, but we have billions of living beings coexisting inside our body.

The brain microbiome

The presence of bacteria in the brain has generated both curiosity and surprise in the scientific community. In fact, one of the first questions to be resolved is how do they get to the brain, since it is protected by the blood-brain barrier.

The blood-brain barrier is a system of protection against the entry of foreign substances and allowing the passage of water, soluble molecules in lipids and some gases. It also allows the selective passage of amino acids and other molecules. But the bacteria found in the brain are, for the most part, of intestinal phylogeny.

They are glial cells that support neurons, astrocytes, which prevent the entry of neurotoxins and other substances into the brain. These harmful substances, when they manage to penetrate the barrier in some way, often produce inflammations with very negative and even deadly consequences. But the funny thing is that astrocytes seem to be the favorite place for these intestinal bacteria to live in the brain.

Although several proposals have been made on how these bacteria have reached there, as for example, through the nerves of the intestine, the blood-brain barrier or the nose, the cause is still unknown. There is still much to investigate about this possible brain microbiome.

The investigation

Dr. Rosalinda Roberts and her team from the Psychiatry and Behavioral Neurobiology at the University of Alabama are responsible for this finding. For this, they studied the brain of 34 people; half were healthy subjects and the other half were suffering from schizophrenia. And in addition, a parallel study with mice was carried out, to rule out that the bacteria appeared only postmortem or there could be any error due to contamination in the study.

In both one and another study, the presence of bacteria in the human brain and in the mice was observed in non-infectious or traumatic situations. In fact, they were found in several brain areas. Mainly in the substantia nigra, the hippocampus and the prefrontal cortex; and very little amount in the striate. Also, none of the brains examined showed inflammation.

These results have left the door open to speculation and new research on the brain microbiome. For now, the possibility that these microbes are related to behavior, mood and some neurological diseases is being considered. Although the results on healthy people encourage to think that they can be beneficial also in the brain, just as they are in the intestine. To this day you can not rule out any possibility.