Second Brain: How Gut Bacteria Control Our Minds

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

We are accustomed to the fact that the brain controls our behavior - but what controls the brain? It turns out that sometimes silent passengers-microbes strive to take control. Bird In Flight understands how not to leave decision-making to bacteria.

The gut and brain communicate through the vagus nerve, which travels down the neck into the chest and abdomen. Julia Anders, author of the bestselling book Charming Gut. How the most powerful organ governs us,”compares the vagus nerve to a telephone wire that connects the intestines to the individual centers of the brain.

The brain conducts all organs of the body, and many through the vagus nerve, but only the intestine has autonomy: if the nerve is cut, "disconnecting" the brain from the intestine, the latter will continue to work. It has its own nervous system, which scientists call "the second brain." It consists of a huge number of neurons and auxiliary cells, and produces several dozen neurotransmitters. The functions of such a developed nervous system cannot be limited to the regulation of digestion.

Hello, are they germs?

Most of the signals along the vagus nerve are not transmitted from top to bottom, but from bottom to top - to the brain. Scientists speculate that the gut affects our mental health. An electrical vagus nerve stimulator is already being used to treat depression that does not respond to drug therapy. It makes the nerve generate the "correct" impulses.

The intestines produce 90% of serotonin, the hormone of happiness. Maybe the cause of depression isn't in the brain, but in the gut. Scientists have also found a link between gut health and anxiety, autism, neurodegenerative diseases such as Parkinson's and Alzheimer's.

Moreover: not only the intestine itself sends signals through the vagus nerve, but also the microorganisms inhabiting it. They do this in different ways - for example, by stimulating the production of serotonin by cells in the intestinal mucosa. The influence of microflora on behavior and mood has been proven in numerous experiments on laboratory mice.

How to assess the mental state of mice? You can put animals in a basin of water and watch how long they will swim: depressed mice give up faster in the fight against troubles. Neuroscientist John Kryan of the Irish National University in Cork added the bacteria Lactobacillus rhamnosus JB-1 to the feed of experimental animals. The mice swam faster and more actively, and their bodies produced fewer stress hormones compared to the control group. Dissection of the vagus nerve negated the effect of the beneficial bacteria.

Not only the intestine itself sends signals through the vagus nerve, but also the microorganisms that inhabit it.

If a certain microflora is associated with a depressive or optimistic attitude towards life, the behavior should change when the bacteria are exchanged. This has been shown in experiments by scientists from McMaster University in Canada. They selected several lines of laboratory mice, which had different characters. When timid mice were transplanted with the microflora of adventure mice, they showed more interest in exploring new objects.

Do you like to communicate? Share bacteria

Gut bacteria also influence the social behavior of laboratory mice. Scientists from Baylor College of Medicine in Houston (USA) studied the relationship between maternal obesity and autism spectrum disorders in offspring. The control group of mice ate normally, and the experimental group received food with a high fat content. As expected, the females from the second group gained extra weight.

Mice from overfed mothers were much less interested in communicating with their relatives than the offspring of the control group. Analysis of the intestinal microflora showed significant differences between the two groups - in both generations. But how to check if the propensity for antisocial behavior is due to bacteria? The answer is simple: to populate the intestines of closed animals with the microflora of sociable relatives.

In an experiment with laboratory mice, this is not difficult: it is enough to place animals in one cage, living together inevitably leads to the exchange of intestinal bacteria. After four to five weeks, the microflora of uncommunicative mice became the same as in the control group, and social behavior returned to normal.

Scientists have found that mice with autistic disorder have a greatly reduced number of the bacteria Lactobacillus reuteri in the intestines. This microorganism affects the production of oxytocin, a hormone that regulates social behavior. A high-fat diet suppresses Lactobacillus reuteri in the mother's intestines, and she passes on her disturbed microflora to her offspring.

The lack of beneficial bacteria and, accordingly, oxytocin during the development of the mouse leads to its asociality. By adding live bacteria, Lactobacillus reuteri, to drinking water, the scientists were able to bring the behavior of experimental animals back to normal.

You are what you eat. And vice versa

Microorganisms may have evolutionary reasons for controlling our behavior. According to scientists, bacteria stimulate their hosts to communicate, because it promotes the exchange of microflora. They are also able to influence the food habits of the host, forcing them to consume foods that promote their growth and reproduction. Perhaps when you can't resist the cake, it's not a weak will, but microorganisms.

Some bacteria like fat, some like sugar, and sometimes obesity comes at the price of their preferences. Microbes can control a host's feeding behavior in many ways: they interfere with the reward system in the brain, alter the sensitivity of taste buds, release substances that affect mood, and also hack the transmission of signals through the vagus nerve.

How to resist microorganisms whose interests do not coincide with our plans to lose weight in the new year? Create competition among them. The more diverse the composition of the gut microflora, the less likely one species will prevail over others and take over the command of the brain.

A diet high in fat and simple carbohydrates depletes the intestinal microflora; to maintain a variety of bacteria, you need to eat more vegetables, fruits and dairy products. A study of the effect of diet on weight, which covered 120 thousand people, showed that the main product for weight loss is yogurt.

Germs for depression

Experiments investigating the effect of gut microflora on the psyche show that depression and anxiety disorder can be treated with probiotics, which are beneficial bacteria. Scientists use a new word for them - psychobiotics.

In a study by Iranian scientists, patients with major depressive disorder received bacterial supplements or a placebo. The psychobiotic included Lactobacillus acidophilus, Lactobacillus casei, and Bifidobacterium bifidum. After eight weeks, patients who took the psychobiotic had significantly improved scores on the Beck Depression Inventory (a widely used test to assess depression) compared with controls.

Japanese scientists investigated the effect of kefir containing the Shirota strain of the bacterium Lactobacillus casei on the psychological state of medical students during an important exam. They found that kefir normalizes levels of the stress hormone cortisol and increases serotonin levels. In addition, the probiotic reduces the manifestation of ailments associated with stress, such as colds and abdominal pain.

Experiments studying the effect of intestinal microflora on the human brain are still at an early stage, and usually a small number of people take part in them, so it is too early to talk about an unequivocally proven link between intestinal activity and mental state. But early studies indicate that the study of psychobiotics is a promising direction. Until the magic pill is invented, help your intestines in proven ways: eat yogurts, vegetables and fruits. Then the bacteria will not take over the brain control panel.