A study published in Gastroenterology shows that probiotics in food may alter brain function in humans.
The discovery that changing the bacterial environment, or microbiota, in the gut can affect the brain carries implications for future research that could point the way toward dietary or drug interventions to improve brain function, the researchers said.
The small study involved 36 women between the ages of 18 and 55. Researchers divided the women into three groups: one group ate a specific yogurt containing a mix of several probiotics twice a day for four weeks; another group consumed a dairy product that looked and tasted like the yogurt but contained no probiotics; and a third group ate no product at all. Functional magnetic resonance imaging (fMRI) scans conducted both before and after the four-week study period looked at the women's brains in a state of rest and in response to an emotion-recognition task in which they viewed a series of pictures of people with angry or frightened faces and matched them to other faces showing the same emotions. This task, designed to measure the engagement of affective and cognitive brain regions in response to a visual stimulus, was chosen because previous research in animals had linked changes in gut flora to changes in affective behaviors.
The researchers found that compared with the women who didn't consume the probiotic yogurt, those who did showed a decrease in activity in both the insula—which processes and integrates internal body sensations, like those from the gut—and the somatosensory cortex during the emotional reactivity task. Further, in response to the task, these women had a decrease in the engagement of a widespread network in the brain that includes emotion-, cognition- and sensory-related areas. The women in the other two groups showed a stable or increased activity in this network.
During the resting brain scan, the women consuming probiotics showed greater connectivity between a key brainstem region known as the periaqueductal grey and cognition-associated areas of the prefrontal cortex. The women who ate no product at all, on the other hand, showed greater connectivity of the periaqueductal grey to emotion- and sensation-related regions, while the group consuming the non-probiotic dairy product showed results in between.
The knowledge that signals are sent from the intestine to the brain and that they can be modulated by a dietary change is likely to lead to an expansion of research aimed at finding new strategies to prevent or treat digestive, mental, and neurological disorders, said Emeran Mayer, Professor of Medicine, Physiology, and Psychiatry at the David Geffen School of Medicine at UCLA and the study's senior author.
"There are studies showing that what we eat can alter the composition and products of the gut flora—in particular, that people with high-vegetable, fiber-based diets have a different composition of their microbiota, or gut environment, than people who eat the more typical Western diet that is high in fat and carbohydrates," said Mayer. "Now we know that this has an effect not only on the metabolism but also affects brain function."