It is the duty of the vagus nerve to orchestrate bodily responses to keep you safe or warn you about danger before you even have a chance to think about it. Without your awareness, it scans the environment for cues of danger, pitching you into high alert to fight or flee or, in extreme situations, shutting you down. It also scans for cues of safety, which allow you enough calm to open you up to socially engage with others.
Vagus means wandering, and the vagus nerve begins at the base of the brain, branches down to the heart, the lungs, and the digestive tract, with stops along the way at the larynx and the diaphragm, before descending into the abdomen. The branches of the vagus nerve enable the organs to adjust instantly to the demands of a person’s surroundings.
The vagus nerve is why your heart races and stomach curdles when you sense a threat and why your breathing slows and your body relaxes when friends welcome you to their house. The vagus nerve is the key player in the autonomic nervous system, which controls your internal organs.
From his decades-long study of the vagus nerve and deciphering the daunting complexities of its operations, neuroscientist Stephen Porges has developed the polyvagal theory, which explains the interconnectedness of body reactivity, cognitive and emotional function, and social behavior. Because information flows both to and from the brain via vagal pathways, the vagus nerve can be thought of as a major mind-body highway. Through the vagus nerve, you react to signals in your environment in ways that calm, alarm, or dysregulate the body, and these states in turn create emotional experience and play out in behavior.
States of visceral calm get relayed up to the brainstem, which then transmits the information to more highly evolved brain structures, allowing full access to the brain’s talents and means of expression and enabling social interaction—which has the effect of perpetuating the state of neural calm. But in potential danger states, such as completely novel environments, those higher systems turn off and we become defensive and on high alert: The vagal circuitry narrows our focus and prepares us to fight or flee—the so-called stress response.
If the danger is so overwhelming that there’s no escape or there’s a feeling of being trapped, a third circuit of vagal operations engineers a shutdown. In this out-of-focus, numb state, social contact becomes an intrusion and is aversive.
The bodily responses are not voluntary, and often people are not aware of what triggered them, although they are likely aware that their heart is pounding or their body is trembling.