The Vagus nerve is the longest cranial nerve in the body. It originates in the brain and travels all the way down to the lower internal organs. It is a fundamental regulator of the parasympathetic nervous system, which controls all the involuntary processes such as digestion, heartbeat, respiration, etc. and is responsible for restoring relaxation after a response to stress or danger (the sympathetic nervous system’s activation).

The strength of the vagus response is called “vagal tone” and it is determined by the variations in the heart-rate that can be measured between inhalation and exhalation. During the inhalation, the heart speeds up and during the exhalation, it slows down. The bigger the difference between these two phases, the higher the vagal tone. A high vagal tone is what we need in order to maintain a state of good health.