Unless you’ve been living under a rock, you’ve heard all about the bacteria living in our guts.”Gut health” is all the rage, and proponents say the little critters living in your belly can affect everything from immunity to mood. But did you know that those same bacteria can live in your head?

A group of Candian researchers recently found the same microbes in cadavers’ brains–and the discovery is rocking the scientific community.

The Gut-brain Axis

In recent years, the gut microbiome has been a hot topic in both scientific communities and popular media alike. But what is this trendy issue all about?

A microbiome is a group of microorganisms in a particular environment–in this case, your digestive tract. They’re known to have an effect on various biological processes such as digestion, protection against pathogens, metabolism . . . and the central nervous system. A rather new discovery, this “gut-brain axis” is a communication system between the GI tract and the brain, allowing gut bacteria to produce things like hormones and neurotransmitters.

And that’s where scientists thought it ended–until recently when a group of researchers found the same bacteria living inside the brains of the deceased. The surprising discovery, just presented at the scientific meeting Neuroscience 2018, happened completely by accident. Researchers were looking for differences in the brains of people with and without schizophrenia, when they kept happening upon the same rod-shaped objects again and again.

Scientists were initially uninterested in the foreign objects but eventually discovered that they were bacteria. Upon further investigation, it turned out that most of the microbes were from groups of bacteria that are typically found in the human gut, known as Firmicutes, Proteobacteria and Bacteroidetes, according to Science Magazine.

A Penetrable Fortress?

Until recently, the brain was thought to be a sort of fortress, separated from the body by a virtually impenetrable barrier of specialized cells. The blood-brain barrier was initially discovered in the 1800s when researchers first noted that dyes injected into the bodies of animals tended not to show up in their brains. Likewise, dyes injected into their brains tended not to appear in the body.


So evolved the concept that a highly selective border existed, allowing only nutrients and certain key molecules to pass through into the brain while keeping most other elements out.

If bacteria were found in or around the brain, it was thought to be a sign of disease. “The brain has always been thought of as a sterile site. To find [bacteria] there doing no harm sort of breaks a lot of the dogma” on this, said Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security in Baltimore, who was not involved in the study.

More Evidence Needed

For now, the results should be taken with a grain of salt. Because the tissues used in the study were harvested from cadavers, more work is needed to rule out the possibility that the brain samples were somehow contaminated after death–peer-reviewed data will conclusively determine if there is, in fact, a brain microbiome.

So far, though, researchers there is no implication that the bacteria cause disease, or that they provide any sort of benefit (like “good bacteria” do in the gut). However, if the bacteria do help to maintain brain health in some way, disturbing them (for example, through antibiotics) could have adverse effects on the body. (In the gut microbiome, disruptions to “good” bacteria are thought to cause a range of issues from weight gain to allergies.)

MORE: When it comes to microorganisms living in the brain, these bacteria at least seem to do no harm. These parasites, on the other hand, will eat your brain alive if they get the chance… and they’re found on a shockingly common food.