The Polyvagal Theory was proposed by Dr. Stephen Porges, a neuroscientist at the University of Illinois, in 1994. This theory is about the autonomic nervous system.

Before the Polyvagal Theory, it was commonly believed that the sympathetic and parasympathetic nervous systems had opposing effects on a single target organ. The parasympathetic nervous system was thought to work during relaxation, while the sympathetic nervous system was active during stress or activity.

The vagus nerve, which is the tenth cranial nerve, makes up 80% of the parasympathetic nervous system. According to the Polyvagal Theory, the vagus nerve in mammals has two branches that evolved differently. These branches form a three-level hierarchy in the autonomic nervous system within an individual.

The term "polyvagal" means "many vagus nerves." This theory provides a new perspective on the evolution of the autonomic nervous system in mammals, especially the function of the vagus nerve.

Clinical psychology, particularly trauma specialists, were the first to pay attention to this theory. Traditional theories of the autonomic nervous system and stress could not explain why rape victims often froze and could not move, even when they wanted to escape or say no. In court, this sometimes led to the mistaken belief that the victim had consented.

The Polyvagal Theory offers a theoretical framework to understand the defense responses of organisms in life-threatening situations, such as rape. It explains medically why states like "freeze response" or "shutdown" occur.