In the late 1990s, neuroscientist Dr. Stephen Porges introduced a revolutionary way to understand how our bodies respond to stress, safety, and connection. Known as the polyvagal theory, this framework reshaped how scientists and medical providers think about the nervous system. 

The autonomic nervous system (ANS) is divided into two branches: the sympathetic, or “fight-or-flight,” responsible for activating the body in moments of stress or danger, and the parasympathetic, which promotes rest and recovery. The polyvagal theory expands this binary model of the ANS by emphasizing the role of the vagus nerve, the tenth cranial nerve that extends from the brainstem and innervates through the heart, lungs, and digestive tract. The vagus nerve is central to the parasympathetic system, and the polyvagal theory proposes that it evolved in stages in response to humans’ unique and adaptive needs for survival and social connection. 

“The vagus nerve is central to the parasympathetic system, and the polyvagal theory proposes that it evolved in stages in response to humans’ unique and adaptive needs for survival and social connection.”

A crucial part of the polyvagal theory is the process by which the body assesses and responds to whether an environment is safe or life-threatening through a subconscious process termed “neuroception.” Neuroception is a primitive process, where, based on sensory input such as the subtle shift in someone’s tone of voice or the sudden silence of a previously noisy street, the nervous system “shifts” ANS states to optimize survival. The three states of the ANS, according to polyvagal theory, are the ventral vagal system, the sympathetic system, and the dorsal vagal system. 

The ventral vagal system is the most evolutionarily advanced pathway and is unique to mammals. Commonly referred to as simply the parasympathetic nervous system, this branch is activated by feelings of safety and social connection, usually when spending time with loved ones, in nature, or after certain meditative practices — resulting in the release of the hormone oxytocin into the bloodstream, steady heart and breathing rates, and muscle relaxation. Behaviorally, this state generally leads to increased feelings of joy, compassion, and calm. 

The sympathetic system activates when the body perceives that safety is threatened, either due to environmental cues or sensory input. Within seconds after activation, adrenaline is released throughout the body, causing an increase in heart rate and blood pressure. Furthermore, non-essential life functions such as digestion decrease, preparing the body to fight or flee from danger. During this system’s activation, feelings like anxiety, anger, panic, and fear are experienced. 

“...the polyvagal theory has been monumental in the medicinal and therapeutic world by providing a new framework for understanding trauma, emotional regulation, and social engagement.”

Finally, the dorsal vagal system is considered the oldest branch in evolutionary terms and is activated when danger feels inescapable — creating a “freeze” state similar to the animal response of thanatosis, otherwise known as “feigning death.” In this state, functions like heart rate, metabolism, and social behavior decrease dramatically while fuel storage increases. In extreme cases, this state can lead to feelings of numbness, dissociation, and depression. Researchers have found that dorsal vagal activation is most common clinically among individuals with Autism spectrum disorder, post-traumatic stress disorder, and those experiencing chronic stress and trauma. 

Polyvagal theory emphasizes that these three states are not entirely separate from one another, but rather exist on a continuum that humans move through on a day-to-day basis. Perception of environmental stimuli and responses to activation are unique to every individual, and the activation of states can be impacted by lived experience, resilience, and baseline states. For example, polyvagal theory states that neuroception is more likely to perceive a threat when the ANS is already in a state of defense, like the sympathetic system. Additionally, a history of adversity or trauma can cause neuroception to perceive a threat and activate defensive systems when there is none. Overall, the fluctuation of ANS states is highly dependent on individual perceptions of how safe one’s body perceives them to be. Understanding the fluctuation of these different response states can help inform overall health. 

Polyvagal theory already informs practices for both therapy and medicine. In psychotherapy, clinicians use “polyvagal-informed” approaches to help define clients’ physiological states and restore a sense of safety before processing trauma. Specifically, in trauma therapy, understanding the body’s automatic responses reframes symptoms not as pathology but as adaptive survival strategies. For individuals who have experienced chronic feelings of unsafety, such as abuse or neglect, the nervous system may become “stuck” in defensive states like the dorsal vagal system. Polyvagal-informed interventions aim to retrain the body to recognize safety cues, reconnect socially, and deactivate defensive states when they’re no longer necessary. 

“Overall, the fluctuation of [Autonomic Nervous System] states is highly dependent on individual perceptions of how safe one’s body perceives them to be.”

In medicine, vagus nerve stimulation (VNS) involves placing a small device and wire around the vagus nerve and sending electrical pulses to manually activate its regulatory benefits. VNS is already used to treat epilepsy and severe depression, and research continues to investigate its potential benefits for other conditions like inflammatory and autoimmune disorders. Polyvagal theory also has several applications for understanding patient responses, trauma-informed care, mind-body interventions, and more. 

Since its founding more than 30 years ago, polyvagal theory continues to evolve, especially in response to its growing popularity in clinical fields. Despite some questions of its scientific validity, specifically related to the evolution of the vagus nerve, the polyvagal theory has been monumental in the medicinal and therapeutic world by providing a new framework for understanding trauma, emotional regulation, and social engagement. At its core, polyvagal theory posits that our capacity to think, connect, and heal depends on how safe our bodies feel.