A new study published in the June issue of Gastroenterology presents the first evidence that dietary probiotics may modulate human brain activity. Previous studies show that changes in rodent gut microbiota alters emotional behavior, signaling mechanisms, and visceral nociceptive reflexes. In addition, a growing body of evidence supports the theory that gut microbiota influence emotional behavior through underlying brain mechanisms.
Previously completed rodent studies demonstrate the important role of gut microbiota in brain development, resultant adult pain responses, and emotional behaviors. A change in adult mice's normal gut flora (via fecal transplants, antibiotics, or probiotics) has also been shown to modify pain, emotional behaviors, and brain biochemistry. These findings suggest microbiota have a homologous effect on normal human behavior by altering brain chemistry and changing metabolic products. This could mean that microbiota play a role in the pathophysiology of psychiatric diseases and chronic abdominal pain syndromes. Still, the underlying mechanisms for these responses remain poorly understood.
In order to explore a similar connection in humans, Danone Research - a multinational food-products corporation--funded a study of healthy women who consumed probiotic-containing yogurt (fermented milk product with probiotic (FMPP)) for 4 weeks. This study recruited 36 healthy women (i.e. women without gastrointestinal or psychiatric symptoms) to consume either FMPP, non-probiotic yogurt, or nothing twice daily for 4 weeks. The fermented milk product with probiotics (FMPP) contained Bifidobacterium animalis subsp Lactis, Streptococcus thermophiles, Lactobacillus bulgaricus, and Lactococcus lactis subsp Lactis.
Participants underwent functional magnetic resonance imaging (fMRI) before and after the intervention in order to measure brain response in a resting state versus during an emotion-recognition task. The emotion-recognition task required the participants to view a series of pictures with angry or scared people and matching to other faces showing the same emotions. This task measured rapid, preconscious, and conscious brain responses to emotional stimuli. The probiotic group showed significantly reduced activity in the functional networks of affective, viscerosensory, and somatosensory cortices during the emotional reactivity task. Women who consumed FMPP also had greater connectivity between the periaqueductal grey matter of the midbrain and cognition-associated areas of the prefrontal cortex during the task. Women who did not consumer probiotic yogurt did not experience any of these neurological changes. Consequently, the study found that ingestion of certain bacterial strains has an effect on the host.
"Chronic ingestion of FMPP" by health women resulted in strong neurological responses in reaction to negative context. In particular, the sensory brain along with the prefrontal cortex, the temporal cortex, parahippocampal gyrus, and the periaqueductal grey matter underwent connectivity changes. Based on previous findings in mice these changes may be induced by either systemic metabolic changes related to FMPP intake or by altered vagal afferent signaling to the nucleus tractus solitarii (NTS) and connected brain regions via PAG.
This is the first evidence of a probiotic interaction with the central processing of emotions and sensation in the human brain. Since limited evidence exists, a beneficial relationship cannot be established nor can findings be applied to anyone other than healthy women. However, further research can identify the signaling pathways between the brain and microbiota and inform treatments for conditions associated with gut dybiosis. Essentially, this study's findings will allow for expanded research to study new strategies in the treatment and prevention of digestive, mental, and neurological disorders.
About Author / Additional Info:
Original study: http://gastrojournal.org/article/S0016-5085%2813%2900292-8/
Lisa Opdycke is a New York-based writer and editor. Lisa is originally from a small town in northeastern Indiana. She completed her undergraduate coursework in Human, Biology, Health, & Society at Cornell University in 2011. She received her Bachelor of Science with honors after completing her honors thesis project entitled, "Bovine Seminal Plasma Protein Loss during Capacitation of Fresh and Frozen-Thawed Sperm." Lisa begins her master's studies in public policy at Brown University in the fall following two years at Weill Cornell Medical College-New York Presbyterian Hospital.