Bacteria Might Live In The Human Brain – And That Has Some Mind-Blowing Implications

Virtual dissection of a healthy adult human head using magnetic resonance imaging (MRI). Dr Flavio Dell'Acqua/Wellcome Collection CC BY

Bacteria are everywhere, from that greasy handrail you touched this morning to the bottom of the seafloor, not forgetting the trillion or so that happily live along your intestinal tract. However, it’s long been thought that the brain of a healthy human is a safe haven away from the world of bacteria.

Now, a potentially revolutionary piece of research is indicating that there are bacteria in our brain, a discovery that could have some truly mind-blowing implications. If this preliminary research is on the money, it could explain the apparent effect gut bacteria has on our brain function, behavior, and emotions.

A team of neurobiologists from the University of Alabama presented their preliminary findings at the annual meeting of the Society for Neuroscience last week.

The idea of healthy brains carrying their own microbiota has been floating around for some time, however, scientists have never been able to pin down any sturdy evidence. In this research, they looked at samples from 34 postmortem human brains – half of which belonged to people with schizophrenia, according to Science – and discovered that all of the brains contained varying amounts of rod-shaped bacteria. Most of the bacteria were located in the substantia nigra, hippocampus, and prefrontal cortex, with smaller numbers in the striatum. 

"If bacteria do get up into the brain either from the gut or nasal passages and reside there in live humans or animals, it is indeed revolutionary," lead author Dr Rosalinda C Roberts, the University of Alabama at Birmingham, told IFLScience. 

To eliminate the possibility that the bacteria’s presence was the result of gut bacteria seeping into the brain after death, the researchers then analyzed a number of sterilized mouse brains, which they processed in precisely the same way, and found that no contamination with bacteria had occurred. This suggests, albeit not definitively, that the human brains didn’t contain bacteria because of contamination after death.

Perhaps most intriguing of all, the bacteria were the same types you’d expect to find in the gut, such as Firmicutes, Proteobacteria, and Bacteroidetes.

The detection of bacteria in the brain is particularly curious because of the blood-brain barrier, a fortress wall of cells near the brain’s blood vessels that guard it against unwanted invaders. If any pathogen, such as bacteria, does make it through this barrier, then it can lead to life-threatening inflammation. The newly discovered bacteria, however, doesn't appear to have any such effect.

So, how did the bacteria get into the brain? Are they from the gut? Do they affect brain activity in any way? The scientists are not certain about any of these questions as it’s still very early days for the research. Nevertheless, with further research into the supposed "brain microbiome", they’re hoping to bust open the door of the deeply mysterious relationship between bacteria, our guts, and our brains.

"These findings are preliminary," warned Roberts. "I've had basically two reactions to the findings: unbridled enthusiasm, or caution. As with all scientific findings, these will have to be peer reviewed and published, and replicated to ameliorate scepticism."

[H/T: Science]

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