Our Brains Have a Microbiome Too

And its health and diversity may influence or cause cognitive decline such as dementia and Alzheimer's

Hiya!

It baffles and intrigues me that despite all the advancements in science and technology, there’s still so much we don’t know — we don’t even know how much we don’t know — about our bodies and how they work. We’ve made some progress recently, however, as scientists discover and learn about the many, many microbial communities that share our bodies.

Scientists have identified these communities on and in us, though experts have long thought our brains are exempt. So the discovery of bacteria, viruses, and fungi in our brains has shocked scientists and revolutionized our understanding of cognitive health and neurodegenerative diseases like Alzheimer’s and Dementia.

The Body’s Microbiome

Our bodies are covered and filled with trillions of bacteria, viruses, and other tiny life, collectively known as the microbiome. Your nasal cavity, mouth, lungs, genitals, skin, scalp, and entire digestive system all have distinctive microbiomes. These microscopic communities are as unique to us as our fingerprints, and while some cause us harm, we can’t survive without most of them.

Despite the prevalence of microbes in our bodies, scientists once considered the concept of the brain hosting a microbiome not just far-fetched but inconceivable. They believed the brain is a sterile organ protected from microbial agents by the blood-brain barrier.

The blood-brain barrier protects us by preventing pathogens in our blood from infiltrating our brains and damaging our neurons. If troublemakers manage to slip through, our brain and central nervous system release a backup defense in the form of microglia, like tiny soldiers that swarm the intruders.

A few viruses or bacteria still manage to break through occasionally and can cause illnesses like encephalitis, which causes extreme inflammation and swelling in the brain. Still, scientists thought such infiltration was rare, and the idea that the brain could host diverse populations of microbes was considered laughable — but that attitude is changing.

Richard Lathe, a molecular biologist at the University of Edinburgh in Scotland, told David Robson of New Scientist:

“The past 20 years has seen a switch from thinking that the human body is some kind of sterile entity to realising that microbes are everywhere.”

Over the last two decades, neuroscientists, including Lathe, have stopped scoffing at the idea that the brain also has a microbiome.

The Not-So Sterile Brain

Neuroscientist Christopher D. Link at the University of Colorado Boulder had a graduate student who floated the idea of the brain having a microbiome a few years ago. In response, Link told Robson, “I stopped him, and I berated him.”

After his initial reaction, however, Link examined the research and found far more evidence supporting his student’s idea than he had ever imagined.