The gut is linked to the brain mainly by the microorganisms in the colon, which communicate with the brain through special nerves such as the vagus nerve. The autonomic nerves of the spinal cord — which are connected to the wall of the intestines and other organs of the abdominal and thoracic cavities — also play an important role in communicating with the brain.

By activating these nerves, messages are sent to the brain to control immune cells including microglia, the brain’s primary immune cells.

In addition, this communication line is a two-way street — the brain sends signals to the intestines and the intestines send signals to the brain.

Under normal conditions, the intestines can send signals to the brain to reduce inflammation in the brain. Likewise, the brain can send signals to the intestines that reduces inflammation in the intestines.

When the intestines are inflamed and contain pathogenic (disease-causing) organisms, signals to the brain can activate microglia, resulting in brain inflammation that can lead to immunoexcitotoxicity in one or even several areas of the brain. This is why chronic inflammation in the intestines is a major factor in the development of neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease.

Bad bacteria in the colon can also cause brain diseases by leaking out of the colon into the bloodstream. When this happens, inflammatory cytokines and immune cells can enter the brain, triggering inflammation and immunoexcitotoxicity.

In most cases of neurodegenerative disease, both of these mechanisms are at play — that is, a leaky gut and stimulation along the vagus nerve.

What all this means is that a healthy gut is critical to preventing or limiting the severity of neurological disorders — not only Alzheimer’s and Parkinson’s, but also strokes, multiple sclerosis, seizures, brain trauma, and several autoimmune disorders.

Unfortunately, most doctors ignore this vital disease[1]causing mechanism and fail to correct probiotic abnormalities in the colon.