A new study provides the first evidence in humans that probiotics in the diet can modulate brain activity.
Megan Brooks, Medscape Medical News / Neurology, May 30, 2013
In a proof-of-concept study using functional MRI (fMRI), researchers found that women who regularly consumed probiotic-containing yogurt showed altered activity of brain regions that control central processing of emotion and sensation. The study was funded by Danone Research.
"This study is unique because it is the first to show an interaction between a probiotic and the brain in humans," lead author Kirsten Tillisch, MD, associate professor, Oppenheimer Family Center for Neurobiology of Stress, David Geffen School of Medicine, University of California Los Angeles, toldMedscape Medical News.
"We can't say whether the effects are beneficial; that will take larger studies with more complex designs. One of the areas this will move to is study of disease groups like irritable bowel syndrome and anxiety," she added.
The results appear in the June issue of Gastroenterology.
Modulating Brain Function
"This is a very important study as up to now most of the evidence that the gut microbiota can influence brain and behavior have emerged from studies in mouse models including our own work (Bravo et al.,PNAS 2011)," John Cryan, PhD, professor and head of the Department of Anatomy and Neuroscience, University College Cork, Ireland, who was not involved in the study, told Medscape Medical News.
"Tillisch and colleagues now have neatly shown that probiotics can also affect resting brain activity in human subjects using neuroimaging techniques. This gives credence to the idea that we may eventually modulate brain function in disease states using probiotics. That said, it is a small study, only in women, and the mechanism as to how the bacteria are inducing their effects remains unclear," Dr. Cryan said.
The study involved 36 healthy women with no gastrointestinal or psychiatric symptoms. Twice daily for 4 weeks, 12 women ate a fermented yogurt product containing the probiotics Bifidobacterium animalis subsp Lactis, Streptococcus thermophiles, Lactobacillus bulgaricus, and Lactococcus lactis subsp Lactis; 11 women ate a nonfermented milk product (controls), and 13 received no intervention.
The women underwent fMRI before and after the intervention to measure resting brain activity and brain responses to an emotion-recognition task in which they viewed a series of pictures of people with angry or scared faces and matched them to other faces showing the same emotions. The researchers say they chose this task because studies in animals have linked changes in gut flora to changes in affective behaviors.
During the emotional reactivity task, the probiotic group showed significantly reduced activity (P = .004) in a widely distributed functional network containing affective, viscerosensory, and somatosensory cortices.
During resting fMRI, the probiotic group showed greater connectivity between the periaqueductal grey matter of the midbrain and cognition-associated areas of the prefrontal cortex.
These changes were not observed in the group that consumed the nonfermented milk product; "thus the findings appear to be related to the ingested bacteria strains and their effects on the host," the authors say.
This study, they say, "clearly demonstrates" an effect of probiotic ingestion on evoked brain responses and resting-state networks in women. However, it was not designed to address the mechanisms mediating this effect.
Going forward, they say, "identification of the signaling pathways between the microbiota and the brain in humans is needed to solidify our understanding of microbiota gut-brain interactions. If confirmed, modulation of the gut flora can provide novel targets for the treatment of patients with abnormal pain and stress responses associated with gut dysbiosis."
"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," Emeran Mayer, MD, professor of medicine, physiology, and psychiatry at the David Geffen School of Medicine at UCLA and the study's senior author, told Medscape Medical News.
The study was supported by Danone Research. Dr. Tillisch received grant funding for this project from the company. Two of the authors are employed by Danone Research. Dr. Mayer and Dr. Cryan have disclosed no relevant financial relationships.
Gastroenterology. 2013;144:1394-1401. Abstract