Polyvagal theory is a scientific model created by Dr. Stephen Porges in 1994 that explains how the autonomic nervous system manages our reactions to safety, danger, and trauma. Unlike older ideas that view stress as a simple on/off switch, this theory proposes a three-level hierarchy of responses.
Three States of Polyvagal Theory
Ventral vagal (safe and social). At the top of the ladder, this state promotes calm, social connection, and feelings of safety. The body rests and repairs itself here.
Sympathetic (mobilization). In the middle, this state triggers a classic fight-or-flight response. Your heart rate increases, and your muscles tense to handle a threat.
Dorsal vagal (immobilization or shutdown). At the bottom, this state causes a freeze or collapse response when a threat feels inescapable. Heart rate and blood pressure drop, leading to numbness or dissociation.
Autonomic Nervous System
The autonomic nervous system is divided into three main functional parts: the sympathetic, parasympathetic, and enteric nervous systems.
Sympathetic nervous system controls the “fight-or-flight” response during stressful or emergency situations. It increases heart rate, widens airways, and releases stored energy.
Parasympathetic nervous system controls the “rest-and-digest” state during calm conditions. It slows the heart rate, lowers blood pressure, and promotes digestion.
Enteric nervous system manages the function of the gastrointestinal tract independently as a specialized mesh-like system of neurons along the digestive system.
The vagus nerve is a major component of the autonomic nervous system.
The vagus nerve originates in the brainstem and innervates the muscles of the throat, circulation, respiration, digestion, and elimination. It acts as the primary nerve of the parasympathetic nervous system, which manages “rest and digest” and involuntary functions.
The vagus nerve is the longest cranial nerve in the body. Known as cranial nerve X (Roman numeral 10), it is the 10th of the 12 cranial nerves and travels from the brainstem down through the neck, chest, and abdomen.
The vagus nerve contains both motor and sensory functions and represents the main component of the parasympathetic nervous system. About 75% to 80% of its fibers are sensory (afferent), sending data from organs to the brain — which means the feedback is critical for homeostasis — while the rest are motor (efferent), regulating organ actions.
Anatomic reality versus theory
Physically, the vagus nerve exists as a single, paired nerve (left and right) which travels down the neck, thorax, and abdomen, branching out to various organs; it does not split into a front (ventral) and back (dorsal) physical trunk along its pathway. Instead, these terms refer to the distinct locations of the nerve’s originating nuclei in the brainstem.
The terms “ventral vagus” and “dorsal vagus” come from polyvagal theory. They describe the relative positions of the cell groups (nuclei) inside the medulla oblongata of the brainstem. The “dorsal” path originates from the dorsal motor nucleus of the vagus, which sits more toward the back of the brainstem. and the “ventral” path originates from the nucleus ambiguus, which sits more toward the front.
The dorsal nucleus of vagus nerve is a group of nerve cells in the brainstem that controls involuntary internal body functions like digestion and heart rate. Found in the medulla oblongata at the lower part of the brainstem, it lies near the floor of the fourth ventricle. It sends out preganglionic parasympathetic motor fibers and controls smooth muscle and glands in the thorax and abdomen.
The nucleus ambiguus is the brainstem structure commonly referred to in neuroanatomical discussions of the “ventral vagal” system, serving as a relatively more forward (ventral) motor center compared to the dorsal motor nucleus. It controls muscles of the pharynx, larynx, and soft palate, and provides parasympathetic cardiac motor fibers that regulate heart rate.
Neuroception: A Core Concept
Neuroception is the subconscious process by which the nervous system scans the environment for cues of safety or danger and evaluates risk from environmental and internal cues without conscious awareness or thought. It acts as an automatic surveillance system evaluating surroundings through sights, sounds, and bodily signals.
A person’s current autonomic state influences how their body interprets incoming cues — a calm state detects safety more easily. The term was coined by Dr. Stephen Porges as part of polyvagal theory.
How trauma affects neuroception
Trauma survivors often experience biased neuroception, misinterpreting safe or neutral cues (like a neutral face or loud noise) as life-threatening. This misinterpretation keeps the nervous system locked in chronic defense modes — hypervigilance — like sympathetic mobilization or dorsal shutdown.
Autonomic Nervous System Responses
Our “fight and flight” response is our survival strategy, a response from the sympathetic nervous system. If you were going to run from tiger, you want this response to save your life. When we have a fight response, we can have anger, rage, irritation, and frustration. If we are having a flight response, we can have anxiety, worry, fear, and panic. Physiologically, our blood pressure, heart rate, and adrenaline increase and it decreases digestion, pain threshold, and immune responses.
Second, we have a “freeze” state, our dorsal vagal state, a response of the parasympathetic system, which is our most primitive pattern; this is also referred to as our emergency state. This means that we are completely shut down, we can feel hopeless. We tend to feel depressed, conserve energy, dissociate, and feel overwhelmed. Physiologically, our fuel storage and insulin activity increases and our pain thresholds increase.
Lastly, our “rest and digest” is a response of the parasympathetic system, also known as a ventral vagal state. It is our state of safety and homeostasis. If we are in our ventral vagal state, we are grounded, mindful, joyful, curious, empathetic, and compassionate. This is the state of social engagement, where we are connected to ourselves and the world. Physiologically, digestion, resistance to infection, circulation, immune responses, and our ability to connect is improved.
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Research
Cait, C. (2024). The vagal paradox: A polyvagal solution. EBSCO.
Hanazawa, H. (2022). Polyvagal theory and its clinical potential: An overview. Brain Nerve.
Kenny, B., & Bordoni, B. (2026). Neuroanatomy, cranial nerve 10 (vagus nerve). StatPearls Publishing.
Porges, S. (2009). The polyvagal theory: New insights into adaptive reactions of the autonomic nervous system. Cleveland Clinic Journal of Medicine.
Porges, S. (2021). Polyvagal theory: A biobehavioral journey to sociality. Comprehensive Psychoneuroendocrinology.
Porges, S. (2023). The vagal paradox: A polyvagal solution. Comprehensive Psychoneuroendocrinology.
Porges, S. (2025). Polyvagal theory: Current status, clinical applications, and future directions. Clinical Neuropsychiatry.
Additional Information
Polyvagal theory: How our vagus nerve controls responses to our environment | Verywell Mind
Polyvagal theory | Psychotrauma
Trauma + the polyvagal theory | Mental Health Collective
Vagus nerve | Cleveland Clinic
Vagus nerve anatomy | Medscape
Vagus nerve: What to know | Web MD
What is polyvagal theory? | Polyvagal Institute
What is the vagus nerve? | Cleveland Clinic
What is the vagus nerve? | Healthline
Window of tolerance & polyvagal theory diagram | Proactive Mindfulness