Our 2nd brain

Our 2nd brain

The intestinal microbiota, which weighs between 1 and 2 kg, represents all the microorganisms present in our intestines. It has two main functions: breaking down food for energy from what we have previously digested and building the immune system. These bacteria are essential to our existence.

Today, research on the gut microbiota is particularly active with more than 25,000 articles published as of September 1, 2019.

Several studies have shown that the gut microbiota has an influence on our brain, including our behavior, and vice versa. Alterations in the composition of the gut microbiota linked to several symptoms or diseases have been identified, such as neurological problems, autism, neurodegenerative disorders (linked to the destruction of neurons), stress and cerebrovascular disease.

Diagram of microbiota deregulation and their impact on the brain (Reference: Sibo Zhu et al. The progress of gut microbiome research related to brain disorders. Journal of Neuroinflammation. 2020).

This microbiota is therefore important both for maintaining the intestinal flora (all of the microorganisms living there) and for the proper functioning and development of the brain.

The brain and more specifically the central nervous system have the ability to modify the environment of bacteria living in our intestines, through the regulation of molecules circulating therein as well as immunity.

Diagram of the central nervous system made up of the brain, cerebellum and spinal cord.

Both exterior and interior factors can have an influence, such as eating habits, lifestyle, infection or early exposure to microorganisms. In particular, ingesting too much fat can have a negative impact on learning abilities. Genetic predisposition, metabolism, immunity, and hormones are internal factors.

The composition of the microbiota is also linked to the morphology of the brain. It is necessary for the proper development of our hippocampus, which has a central role in memory and spatial navigation, but also for glial cells (see article on "Myths of the brain").

Diagram of the geography of the brain with the location of the hippocampus.

 It is now accepted that the microbiota plays a role in depression and anxiety behaviors. In the article "Stress Hormones", we saw that in response to stress one area of ​​the brain in particular was activated: the PAH or adrenal hypothalamic-pituitary axis.