The brain is not solely responsible for the nerve processes involved in controlling our thoughts, emotions and movements. According to fascinating recent studies, the gut and spinal cord also contain complex arrangements of neurons that are absolutely essential to the functioning of the body.
The intestine has an independent nervous system, capable of controlling the secretions and movements necessary for the progression of food throughout the digestive system. The size of this “second brain” is far from negligible: 200 million neurons, or as much as the brain of a dog! In addition to fine-tuning the digestion process, these enteric neurons are constantly in contact with the main brain.
Each of us knows very well how deep down we can feel an emotion, for example the famous “fear in the stomach” associated with a stressful event. What is less known, however, is that this communication also works in reverse and that what takes place in the intestine can influence the function of the main brain. During indigestion, for example, the digestive nervous system informs the brain that an unpleasant event has occurred and the brain treasures the memory of the smells, tastes and physical sensations caused by this episode. This memory is so effective that the mere fact of seeing an image or smelling a smell that recalls this food is very often enough to reproduce the unpleasant sensation it had previously caused (heavy or abdominal pain, for example).
Fascinating observations indicate that this communication between the intestine and the brain would also involve serotonin, a neurotransmitter essential to the management of emotions. About 90% of all serotonin in the body is made in the gut and scientists have recently shown that this production is a consequence of the intense metabolic activity generated by the billions of bacteria found in the gut. As the role of serotonin in the control of moods is well established, this observation shows once again to what extent these two brains cooperate to maintain the balance of the organism, both physically and psychically. Like what the ancient Taoists were not wrong to say that there must be harmony between the head (reason) and the stomach (emotions)…
And three brains
Recent observations also suggest the existence of another brain, the one involved in controlling balance. When we walk, sensors on the soles of our feet detect movement and subtle changes in pressure, and send signals to the spinal cord and then to the brain to let it know what’s going on. The brain then uses this information to make the limbs move correctly in order to maintain balance and prevent a fall. We can also witness in real time the establishment of these nervous circuits when a child learns to walk.
According to work carried out by a team of Californian scientists, this adaptation is made possible by the existence of a group of specialized neurons located in the spinal cord. This “mini-brain” integrates all of the information from both the brain and the sensory sensors of the feet to precisely coordinate the position of the limbs, a function particularly important for fine motor skills, for example when one has to move. – place on a slippery surface. Combined with the vestibular system contained in the inner ear, vision and sensors located on the muscles, tendons and joints, this mini-brain therefore allows fine regulation of balance maintenance.
These observations illustrate how central the nervous system is to the interaction of the human body with the outside world. Considering the astronomical sum of events to which we are exposed daily and the importance of adapting quickly to these changes, we must admit that three brains are not too many!
Yano JM et al. Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis. Cell 2015;161:264-76.
Buran S et al. Identification of a spinal circuit for light touch and fine motor control. Cell 2015; 160:503-15.