Influence of gut microbiota on the structure of brain and human emotions.

iStock_000015704019XSmallInfluence of gut microbiota on the structure of brain and human emotions.

The more we learn about microorganisms that inhabit our organism, the more we realize how great influence they have on various aspects of our life, starting from our physical health and mental wellbeing as far as our thoughts and emotions. According to the recent studies of international group of scientists, there is a correlation between gut microbiological profile and function of the brain, which can result in different emotional reactions. Scientists claim, that it is the first evidence found for behavioral differences related to microbiome among healthy humans. The study was published in Psychosomatic Medicine.

Microorganisms are part of human physiological flora and considerably impacts on its functioning. Majority of them is found in the digestive system and consists of 10 13 -10 14 bacterias. They can modulate immune system, affect proliferation of epithelial cells in the intestines and also enrich the whole metabolism, which has great influence on maintaining health. All changes in the intestinal environment result in changes in microbiome’s composition, means the genomes of microorganisms that microflora is composed of. That affects the state of our physical health (e.g. development of inflammatory bowel disease) and our psychological state, as we learnt.

The possibility of the influence of gut microbiome on human health and sickness has been widely brought up since last few years and encouraged scientists to further research of its many aspects, including correlation with human brain. Previous reports have reffered to the issue of the so called “gut-brain axis”. The role of microbiota – microorganisms in synthesis of naurotransmitters (serotonin, melatonin, GABA, acetylocholine, histamine, catecholamines) is emphasized and it is also taken into consideration as a pathogenic factor of neuropsychiatric diseases (e.g. depression). Does the microbiome really affect human emotional reactions? The most recent research on this topic was carried by international science group led by Kirsten Tillisch from University of California in Los Angeles, whose results were published in Psychosomatic Medicine. The researchers showed correlation between two types of bacterial flora of the intestines and human emotional reactions. They claim, that it is the first evidence found for behavioral differences related to microbiome in healthy humans.

Previous researches of the gut – brain axis were carried on animals and have shown that changes in regulations of rodents’ gut microflora can affect their behavior. Tillisch et al. started their research directly on humans. The studied group consisted of 40 healthy women aged 18 – 55 years, with no history of probiotics or antibiotics usage. The faecal samples were taken from the participants. Analysis with pyrosequencing methods was performer and participants were divided into two groups based on its results. One group showed a greater abundance of Bacteroides spp and the second one – Prevotella spp. Then, brains of the participants were scanned via functional magnetic resonance imaging. The test involved showing images that were supposed to provoke a positive, negative or neutral emotional reaction.

After the analysis of their results, scientists found that group with a greater abundace of Bacteroides spp. in their guts showed greater thickness of the grey matter in the frontal cortex and insula in comparison to the group with predominance of Prevotella spp. This brain regions are responsible for complex information processing. Furthermore, the study showed that the same group has a larger volume of the hippocampus – the region involved in memorising. On the other hand, women with greater abundance of Prevotella spp. demonstrated lower volume in the previously mentioned areas, but at the same time they presented more connections between emotional, attentional and sensory brain regions. When negative images were shown to the women with dominance of Prevotella spp., lower activity of hippocampus was observed, but at the same time – higher levels of anxiety, distress and irrability were reported. According to scientists, this could be a result of the fact that hippocampus helps us to regulate emotions, so with its lower volume – probably related to the characteristics of gut microflora – negative images can have greater emotional impact.

Further researches are needed for development of the topic and solving the problem. Although the studied group in the latest research was small, Tillisch et al. have shown the new direction of studies about human microbiome and its influence on health and sickness. For sure, there is a correlation between gut microbiome and emotions. So, can diet help us change the way of our perceiving the world?

Authors: Rafał Kuś, Monika Hałgas, Małgorzata Kozioł

Tillisch K., Mayer E., Gupta A., Gill Z., Brazeilles R., Le Nevé B., van Hylckama Vlieg JET, Guyonnet D., Derrien M., Labus JS.: Brain structure and response to emotional stimuli as related to gut microbial profiles in healthy women. Psychosom Med. 2017, Jun 28. doi: 10.1097/PSY.0000000000000493.
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