You can’t have a thought, feeling, sensation, or mental image without calling upon your brain, and this close relationship makes us human. Since 100 billion brain cells are constantly generating your mental life, no relationship seems more important, and everyone has a fear in the back of their mind about what might happen in old age if Alzheimer’s strikes, in essence destroying the mind-brain connection.
But as precious as this relationship is, your brain has a more important relationship that was hidden until about twenty years ago. This precious relationship is with bacteria, and even when you are asleep or thinking about nothing at all, the communication never ceases between the brain and bacteria, specifically the bacteria in your gastrointestinal tract (the gut microbiota).
Between them the brain and your GI tract have created a real-life matrix, just like the one in science-fiction. You are alive and relate to your brain inside this tight structure of biochemicals that carry thousands of messages per second between microbiota and brain. At first sight this seems unbelievable, because few life forms have genetics as rudimentary as a bacterium, and no life form has a brain as complex as the human brain. An old proverb says that even a cat can look at a king. Biologically speaking, the lowly bacterium (along with viruses and microscopic fungi) does a lot more than look at your brain, more even than eavesdropping on it.