Can gut bugs make you smarter?

I have some startling news: you are not human. At least, by some counts. While you are indeed made up of billions of human cells working in remarkable concert, these are easily outnumbered by the bacterial cells that live on and in you – your microbiome. There are ten of them for every one of your own cells, and they add an extra two kilograms (4.4lbs) to your body. 

Far from being freeloading passengers, many of these microbes actively help digest food and prevent infection. And now evidence is emerging that these tiny organisms may also have a profound impact on the brain too. They are a living augmentation of your body – and like any enhancement, this means they could, in principle, be upgraded. So, could you hack your microbiome to make yourself healthier, happier, and smarter too?

According to John Cryan, this isn’t as far-fetched as it sounds. As a professor of anatomy and neuroscience at University College Cork, he specialises in the relationship between the brain and the gut. One of his early experiments showed the diversity of bacteria living in the gut was greatly diminished in mice suffering from early life stress. This finding inspired him to investigate the connection between the microbiome and the brain.

The bacterial microbiota in the gut helps normal brain development, says Cryan. “If you don’t have microbiota you have major changes in brain structure and function, and then also in behaviour.” In a pioneering study, a Japanese research team showed that mice raised without any gut bacteria had an exaggerated physical response to stress, releasing more hormone than mice that had a full complement of bacteria. However, this effect could be reduced in bacteria-free mice by repopulating their gut with Bifidobacterium infantis, one of the major symbiotic bacteria found in the gut. Cryan’s team built on this finding, showing that this effect could be reproduced even in healthy mice. “We took healthy mice and fed themLactobacillus [another common gut bacteria), and we showed that these animals had a reduced stress response and reduced anxiety-related behaviours.”

But why should bacteria in the gut affect the brain? There are several different ways that messages can be sent from one organ to the other. It can be hormones or immune cells via the bloodstream, or by impulses along the vagus nerve, which stretches from the brain to intertwine closely with the gut. Through these pathways, actions in one produce effects in the other.

So how might you go about altering your microbiome to do a spot of brain-hacking? Cryan’s team works on several fronts, investigating the potential to manage stress, pain, obesity and cognition through the gut. “We have unpublished data showing that probiotics can enhance learning in animal models,” he tells me. His team tested the effects of two strains of bacteria, finding that one improved cognition in mice. His team is now embarking on human trials, to see if healthy volunteers can have their cognitive abilities enhanced or modulated by tweaking the gut microbiome.

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