Now that we know that gut bacteria can speak to the brain—in ways that affect our mood, our appetite, and even our circadian rhythms—the next challenge for scientists is to control this communication. The science of psychobiotics, reviewed October 25 in Trends in Neurosciences, explores emerging strategies for planting brain-altering bacteria in the gut to provide mental benefits and the challenges ahead in understanding how such products could work for humans.
Psychobiotics is a recent term. While it’s been known for over a century that bacteria can have positive effects onphysical health, only studies in the last 10-15 years have shown that there is a gut-brain connection. In mice, enhancedimmune function, better reactions to stress, and even learning and memory advantages have been attributed to adding the right strain of bacteria. Human studies are more difficult to interpret because mood changes in response to probiotics are self-reported, but physiological changes, such as reduced cortical levels and inflammation, have been observed.
“Those studies give us confidence that gut bacteria are playing a causal role in very important biological processes, which we can then hope to exploit with psychobiotics,” says Review lead author Philip Burnet, an associate professor of psychiatry at the University of Oxford. “We’re now on the search for mechanisms, mainly in animal models. The human studies are provocative and exciting, but ultimately, most have small sample sizes, so their replicability is difficult to estimate at present. As they say, we’re ‘cautiously optimistic.'”