As clinicians, providing our clients with education on their brain is vital to clinical outcomes. The human brain is the command center for the nervous system and impacts thoughts, feelings, and behaviors. Polyvagal Theory focuses on the vagus nerve which is the 10th cranial nerve and starts in the brain.

The vagus nerve begins in the medulla oblangata, which is the lower part of the brainstem. The medulla oblangata manages cardiac, respiratory, and vasomotor functioning and impacts the autonomic nervous system functions of breathing, heart rate, and blood pressure. 

The vagus nerve is a bidirectional highway that starts in the medulla oblangata and ends in the gut. Signs from the gastrointestinal track activate the hippocampus, the place where memories are stored in the brain. 

The amygdala is closely linked to the hippocampus. It detects and processes fearful and threatening stimuli. Once the amygdala is activated, the brain uses the two branches of the vagus nerve to react to the threat. The hypothalamus activates the sympathetic nervous system and sends a signal to the adrenal glands to release epinephrine into the bloodstream. As this hormone circulates through the body, physiological changes occur such as the heart rate increases, and blood is pumped into major organs.

The hypothalamus’ main job is to keep the body in homeostasis. It communicates with the rest of the body through the autonomic nervous system and receives chemical messages from nerve cells in the brain and from nerve cells in the body (your peripheral nervous system), which is also responding to signals outside the body.

Stimulation of the vagus nerve decreases conditioned fear responses in the pathway that connects the prefrontal cortex and the amygdala. 

The vagus nerve is involved in the interoceptive awareness (internal sensations related to emotions and reaction to stress) via the insula.