Probiotic mixture affects brain responses in an emotional task (EAT)

Probiotics can affect brain function via the microbiome-gut-brain axis. Evidence in humans remains limited. The present proof-of-concept study investigated if a probiotic product containing a mixture of Bifidobacterium longum R0175, Lactobacillus helveticus R0052 and Lactiplantibacillus plantarum R1012 affected functional brain responses in healthy subjects during an emotional attention task.In this double-blinded, randomized, placebo-controlled crossover study (NCT03615651), 22 healthy subjects were exposed to a probiotic intervention and a placebo for 4 weeks each, separated by a 4-week washout period. Subjects underwent functional magnetic resonance imaging while performing an emotional attention task after each intervention period. Differential brain activity and functional connectivity were assessed. Altered brain responses were observed in brain regions implicated in emotional, cognitive and face processing. BNA region-based analysis (emotional vs. control condition) demonstrated reduced activation in the parahippocampal gyrus, hippocampus, amygdala, basal ganglia and cingulate gyrus and increased activation in the orbital gyrus and precuneus after probiotic intervention compared to placebo. Increased activation in the orbitofrontal cortex was also found after probiotic intervention compared to placebo using a cluster-based analysis. Significantly reduced task-related functional connectivity was observed after the probiotic intervention compared to placebo. Fecal microbiota composition was not majorly affected by probiotic intervention. The probiotic intervention resulted in subtly altered brain activity and functional connectivity in healthy subjects performing an emotional task without major effects on the fecal microbiota composition. This indicates that the probiotic effects occurred via microbe-host interactions on other levels. Further analysis of signaling molecules could give possible insights into the modes of action of the probiotic intervention on the gut-brain axis in general and brain function specifically.