In the past few years, there has been an increasing amount of evidence showing that changes in the gut microbiota can affect brain physiology and human behavior. Cognition, which was originally believed to be controlled solely by the CNS (central nervous system), is now suspected to also be affected by several non-CNS factors, including the gut microbiome in the gastrointestinal tract. Additionally, the gut microbiome may also play a role in cognitive dysfunction, neurodegeneration, and several neurological diseases.
The idea that the gut microbiome affects our brain isn't relatively new, however the attention it has been getting from scientists has been renewed in the last 15 years. Researchers are beginning to reinforce the relationship between the gut microbiome and the brain through studies, often involving mice. While questions do remain about how gut-brain communication occurs and whether it can be used for scientific and therapeutic purposes, many scientists claim that the gut-brain scientific field is still in its early days. Nevertheless, they are optimistic that they will find answers to these questions.
The human gut houses trillions of microbes. Some of these microbes may be harmful and are there to cause damage, while others are part of our anatomy as they help our bodies in carrying out various tasks, such as digesting food. These "good microbes" take in nutrients and then pump out a raft of new chemicals. The gut microbiome is a diverse ecosystem of bacteria, viruses, and fungi. In exchange for raw materials and shelter, these microorganisms feed and protect their hosts.
The microbiome's influence on our lives doesn't end there. Various studies have shown a connection between gut microbes and neurological conditions such as autism, epilepsy, and depression. As of now, researchers and scientists don't fully understand how the brain and the gut are linked but they suggest that understanding the mechanism which connects the two organs could one day lead to treatments for many neuropsychiatric disorders.
One theory for how the gut microbiome interacts with the brain involves the bacteria releasing chemicals into the bloodstream which can have an effect on the brain. The CNS alters the intestinal environment by regulating gut motility and secretion, as well as mucosal immunity through the neuronal-glial-epithelial axis and visceral nerves. External factors such as dietary habit, lifestyle, infection, and early microbial exposure, as well as internal factors such as genetics, metabolism, immunity, and hormones, regulate the composition of the gut microbiome.
Bacteria may respond to these changes by producing neurotransmitters or neuromodulators in the intestine, which circulate from the blood to the brain. These modulators may include bacteria derived choline, tryptophan, short-chain fatty acids, and intestinally released hormones which include ghrelin and leptin.
Doctors have been wondering about the links between digestion and mental health since the 19th century. Inspired by Louis Pasteur, the famous scientist who speculated in 1885 that animals which lacked internal microbes to regulate bodily processes would die, European doctors began to investigate the significance of microbes in the digestive system. The doctors suggested that the toxins produced by microbes in the gut may be poisoning the minds of their patients. This area of study soon became very popular for a few decades before being discredited and untouched until recently.
Scientists and researchers believe there is a lot of potential in the field and that continued research and experimentation could lead to the development of therapies and treatments for neurological disorders and diseases. Additionally, it’s incredibly appealing to think that, in the future, some minor adjustments to diet could help treat neurological diseases.