REMEMBER the last time you had a stomach bug and just wanted to crawl into bed and pull up the covers? That is called “sickness behaviour” and it is a kind of short-term depression. The bacteria infecting you aren’t just making you feel nauseous, they are controlling your mood too. It sounds absurd: they are in your gut and your feelings are generated in your brain. In fact, this is just an inkling of the power that microbes have over our emotions.
In recent years, such organisms in the gut have been implicated in a range of conditions that affect mood, especially depression and anxiety. The good news is that bacteria don’t just make you feel low; the right ones can also improve your mood. That has an intriguing implication: one day we may be able to manipulate the microbes living within our gut to change our mood and feelings.