“The thought of parasites preying on your body or brain very likely sends shivers down your spine. Perhaps you imagine insectoid creatures bursting from stomachs or a malevolent force controlling your actions. These visions are not just the night terrors of science-fiction writers—the natural world is replete with such examples.

“Take Toxoplasma gondii, the single-celled parasite. When mice are infected by it, they suffer the grave misfortune of becoming attracted to cats. Once a cat inevitably consumes the doomed creature, the parasite can complete its life cycle inside its new host. Or consider Cordyceps, the parasitic fungus that can grow into the brain of an insect. The fungus can force an ant to climb a plant before consuming its brain entirely. After the insect dies, a mushroom sprouts from its head, allowing the fungus to disperse its spores as widely as possible.”

That’s the introduction to my feature article about how the microbes in your gut might influence your brain and behaviour, which is out now in the July/ August issue of Scientific American MIND. The article focuses mainly on the work of Jane Foster and John Bienenstock of McMaster University in Ontario and John Cryan of University College Cork, who have been collaborating on experiments designed to test how certain species of gut bacteria influence the activity of genes in the brain. Below is a story I wrote last year about some of the work from Foster’s group, updated to include quotes and new research that has been published since I wrote the feature.

Gut bacteria may influence thoughts and behaviour