Scientists have long believed that bidirectional communication exists between the gut and the brain. In fact, evidence suggesting that the gut microbiota — the diverse community of microbes living in the human gut — interacts with the central nervous system (CNS) and influences brain function has increased over the years. Recent studies even propose that this happens via several pathways, which include neural pathways, endocrine pathways, and immune pathways. Because of its link to the CNS, researchers nowadays try to modulate the human gut microbiota in the hopes of improving human behavior and other aspects of mental health.
In a new study that appeared in The American Journal of Gastroenterology, researchers from Germany, Ireland, and Italy investigated the effect of a probiotic strain known as Bifidobacterium longum 1714™ on human brain function in response to social stress. B. longum 1714™ is a food supplement that’s currently being marketed under the brand Zenflore. The researchers reported that this probiotic strain can not only reduce mental fatigue, it can also regulate neural responses during social stress that help suppress negative emotions.
A probiotic that helps modulate the gut-brain axis
Previous investigations have shown that the probiotic strain Bifidobacterium can not only reduce anxiety in mice, it can also improve cognition and stress responses by modulating brain processes. In humans, the effects of probiotics consumption on brain activity have been a subject of scientific interest for quite some time.
The earliest studies involved the use of functional magnetic resonance imaging (MRI). Results of human experiments showed that probiotic supplementation could alter brain activations and affect emotional responses in healthy participants after four weeks of intervention. (Related: Probiotics fight depression: Healthy gut bacteria found to reduce symptoms.)
In a bid to further understand how this works and identify the effects of a specific bacterial strain, the researchers conducted a randomized, double-blind, placebo-controlled trial involving healthy men and women aged 18 to 50 years. They used a neuroimaging method called magnetoencephalography (MEG) to explore the effects of B. longum 1714™ on brain function following exposure to a social stressor.
The researchers used a standardized paradigm called Cyberball Game (CBG) to induce social stress by social exclusion or rejection. They hypothesized that supplementation with B. longum 1714™ for four weeks can alter the resting-state brain activity and neurophysiological responses of healthy participants to CBG-induced social stress.
The researchers measured the brain activity of each participant before and after probiotic intake, and prior to and during the game. Before social stress was induced, they noted that the probiotic strain influenced brain activity in a way that correlated with enhanced vitality and reduced mental fatigue.
Meanwhile, during CBG, the researchers found that B. longum 1714™ intake influenced the central processing of stress stimuli. According to previous studies, the prefrontal cortex (PFC), temporal cortex, and anterior cingulate cortex (ACC) are the three brain regions involved in neural processing of CBG-induced stress.
The researchers confirmed this through MEG and reported that B. longum 1714™ was able to modulate neural responses in these regions during social stress. This was evidenced by changes in neural oscillations both in the PFC and the ACC. The researchers believed that these changes correspond to the counter-regulation of negative emotions in response to social stress.
“As researchers in the placebo effect, we have been [skeptical] about many of the claims made about probiotics and the gut-brain axis,” said Paul Enck, a researcher from the University of Tubingen in Germany and one of the authors of the study.
“We think the results are novel and innovative and provide a scientific basis to assess the true impact of specific bacterial strains on the brain,” he added.
Enck and his colleagues did not investigate the clinical effects of B. longum 1714™ because their study was not designed to detect differences in subjective stress. Their only focus was the probiotic strain’s effect on the brain.