Until recently, there was little evidence to show a direct connection between the immune system of the body and the central nervous system. But Dr. Kevin Tracey, a neurosurgeon based in New York, changed all that when he discovered that the immune system and the central nervous system are joined after all.
Rat model experimentation taught Tracey and his team that when they injected an anti-inflammatory into the brain, it also blocked inflammation in the spleen and in other organs in the rest of the body.
Since they knew they had injected too small an amount to travel to the spleen, they realized that the response had to have come from the brain itself, specifically stimulation of the vagus nerve.
The brain seemed to use the vagus nerve of the nervous system to tell the spleen to turn off inflammation throughout the body.
The vagus nerve got its name from the Latin, meaning "wandering". That's because it's very long, meandering down the neck on each side, across the chest, through the abdomen.
It's in communication with the brain about the digestive tract, the heart, intestines, kidneys, liver, lungs and spleen. It also communicates about many other nerves that participate in eye contact, facial expression, speech and comprehension of voices.
The vagus nerve has thousands of sensory fibers, among other types of fibers, and it talks to your brain about it all.
You're not aware of this communication that is going on all the time. The vagus nerve is important to the parasympathetic nervous system and calms your organs down after adrenaline surges of your stress response. It works better in some people than in others.
When you breathe in, your heart rate speeds up, moving oxygenated blood more quickly through your body. Breathing out makes your heart slow down. The vagus nerve is suppressed when breathing in, and is activated when breathing out.
The greater the contrast in your heart rate between breathing in and out, the higher your vagal tone, that is the stronger your vagal response, will be. An electrocardiogram can measure this response.
The higher your vagal tone, the more efficient you are at managing your blood sugar levels.