How Gut Bacteria Are Controlling Your Brain

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Looking after the multitudes of bacteria, fungi and other microorganisms living in our guts could help us think better and even offer new ways of treating mental health conditions. Your gut is a bustling and thriving alien colony. They number in their trillions and include thousands of different species.

Many of these microorganisms, including bacteria, archaea and eukarya, were here long before humans, have evolved alongside us and now outnumber our own cells many times over. Indeed, as John Cryan, a professor of anatomy and neuroscience at University College Cork, rather strikingly put it in a TEDx talk: “When you go to the bathroom and shed some of these microbes, just think: you are becoming more human.”

Collectively, these microbial legions are known as the “microbiota” – and they play a well-established role in maintaining our physical health, from digestion and metabolism to immunity. They also produce vital compounds the human body is incapable of manufacturing on its own.

But what if they also had a hotline to our minds? In our new book, Are You Thinking Clearly? 29 Reasons You Aren’t And What To Do About It, we explore the dozens of internal and external factors that affect and manipulate the way we think, from genetics, personality and bias to technology, advertising and language. And it turns out the microbes that call our bodies their home can have a surprising amount of control over our brains.

Over the last few decades, researchers have started to uncover curious, compelling – and sometimes controversial – evidence to suggest that the gut microbiota doesn’t just help to keep our brains in prime working order by helping to free up nutrients for it from our food, but may also help to shape our very thoughts and behaviour. Their findings may even potentially bolster how we understand and lead to new treatments for a range of mental health conditions, from depression and anxiety to schizophrenia.

The picture is still very far from complete, but in the wake of the Covid-19 pandemic, which has had a deleterious impact on people’s mental health in many parts of the world, unpicking this puzzle could be more important than ever.

One of the research field’s key origin stories took place in the North American wilderness – and, be warned, it makes for some stomach-churning reading. The year was 1822 and a young trader named Alexis St Martin was loitering outside a trading post on what is now called Mackinac Island, in what is now Michigan, when a musket accidentally went off next to him, firing a shot into his side from less than a yard (91cm) away.

His injuries were so bad that part of his lungs, part of his stomach and a good portion of his breakfast that day spilled out through the wound in his left side. Death seemed certain, but an army surgeon named William Beaumont rode to the rescue and saved St Martin’s life, although it took the best part of a year and multiple rounds of surgery.

What Beaumont couldn’t repair, however, was the hole in his patient’s stomach. This persistent fistula would remain a grim and lasting legacy of the accident, but Beaumont wasn’t one to pass up a good opportunity – however unpleasant. Realising that the hole provided a unique window into the human gut, he spent years investigating the intricacies of St Martin’s digestion.

Exactly how willing a volunteer St Martin was is open to debate as Beaumont employed him as a servant while conducting research on him – the murky arrangement almost certainly wouldn’t be considered ethical today. Among the findings Beaumont uncovered during his studies of St Martin’s guts, however, included how they were affected by its owner’s emotions, such as anger.

Through this finding, Beaumont, who would go on to be lauded as the “father of gastric physiology“, had hit upon the idea of a “gut-brain axis” – that the gut and the brain aren’t entirely independent of one another but instead interact, with one influencing the other and vice versa. And now we know that the microorganisms within our gut make this process even more complex and remarkable.

“More and more research is revealing that the gut microbiome can influence the brain and behaviour across a variety of different animals,” says Elaine Hsiao, associate professor in integrative biology and physiology, at the University of California, Los Angeles (UCLA).

It’s important to remember that the microbes were here before humans existed, so we have evolved with these ‘friends with benefits’ – John Cryan

How exactly our microbiota might be influencing our mind is a growing, pioneering and still relatively novel field. But there have been advances over the last 20 years or so, particularly in animals. And, slowly, a case is being built to suggest that these microorganisms aren’t just a vital part of our physical selves, but also our mental and emotional selves, too.

“In medicine, we tend to compartmentalise the body,” says Cryan. “So, when we talk about issues with the brain, we tend to think about the neck upwards. But we need to frame things evolutionarily. It’s important to remember that the microbes were here before humans existed, so we have evolved with these ‘friends with benefits’. There has never been a time when the brain existed without the signals coming from the microbes.

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By Miriam Frankel and Matt Warren

Source: How gut bacteria are controlling your brain – BBC Future

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