Previous data in animals and humans have shown the potential of manipulating the gut microbiome to modify emotional and cognitive behavior and brain function. For instance, Bifidobacterium longum 1714 has been tested for central effects in mice and humans, but studies assessing how probiotics may affect behavior and brain function in healthy volunteers are scarce.
A new double-blind, placebo-controlled randomized study, led by Dr. Veronika Schöpf of the Institute of Psychology at University of Graz (Austria), has found that healthy volunteers who took a probiotic for 4 weeks showed changes in emotion-related brain activation patterns.
The researchers sought to study the effects of administering 4 weeks’ worth of multi-strain oral probiotics on behavior, brain function and gut microbial composition in healthy volunteers (20-40 years). Participants were divided equally into three groups: one active intervention group (probiotic) and two control groups (placebo and no intervention), with 15 participants in each group. Functional magnetic resonance imaging (fMRI) was used to measure changes in emotion-related brain activation patterns. Stool samples were collected to investigate the gut microbial composition before and after the probiotic intervention.
Probiotic administration for 4 weeks improved self-reported behavioral measures of positive affect (in terms of hopelessness and risk aversion) and cognitive reactivity, as measured with four self-reported depression and anxiety questionnaires, namely, Positive and negative affect schedule (PANAS), Symptoms checklist-90 (SCL-90), Allgemeine Depressionsskala (ADS), and Leiden index of depression severity (LEIDS).
Probiotic administration was also associated with changes in brain activation patterns in response to emotional memory and emotional decision-making tasks. Besides this, blood oxygenation level signal changes in fMRI emotion recognition tasks correlated with self-reported behavioral measures in the probiotic group. Probiotic participants changed their decision about the selection of the most unpleasant stimuli less frequently than the control subjects during the emotional decision task. Furthermore, the influence of the probiotic on decision-making processes was reported by changes in neural activity in the cingulum and precuneus in the emotional decision task. These results show that probiotic-induced changes in self-reported measures of emotional behavior can be confirmed by measuring neural correlates of emotional decision-making and emotional memory processes.
On the other hand, changes in emotion-related brain activation patterns were also accompanied by subtle but significant shifts in the gut microbiota composition. In this regard, two operational taxonomic units belonging to Bacteroides sp. (a well-known producer of short-chain fatty acids) and Alistipes sp. increased in the probiotic group.
Finally, a relationship was found between gut microbial composition, blood oxygenation level signal changes in the cingulum and cerebellum and behavioral measures. Due to the involvement of cingulum and cerebellum in decision-making and emotional processing, these results suggest that probiotic effects on behavior are reflected in imaging measures. Furthermore, microbial composition was associated with self-reported behavioral measures. Specifically, the scores from the depression questionnaire ADS were associated with a higher abundance of metabolic pathways involved in starch and sucrose metabolism.
In conclusion, these data show the distinct probiotic influence at behavioral, neural and microbiome levels in healthy volunteers. These results are in line with a well-known study led by Professor Emeran Mayer, which showed how administration of a fermented milk product with a probiotic for 4 weeks affected the activity of brain regions involved in controlling the central processing of emotion and sensation; they are also in line with a study from McMaster University.
Bagga D, Reichert JL, Koschutnig K, et al. Probiotics drive gut microbiome triggering emotional brain signatures. Gut Microbes. 2018; doi: 10.1080/19490976.2018.1460015.
 7.5 x 106 colony forming units/g containing nine bacterial strains: Lactobacillus casei W56, Lactobacillus acidophilus W22, Lactobacillus paracasei W20, Bifidobacterium lactis W51, Lactobacillus salivarius W24, Lactococcus lactis W19, Bifidobacterium lactis W52, Lactobacillus plantarum W62 and Bifidobacterium bifidum W23.