Understanding the Polyvagal Theory and the Triune Brain: Why We Fight, Flee, or Freeze
Have you ever found yourself reacting to stress in a way that surprises you—snapping at someone, going numb, or suddenly fleeing a situation? These instinctive responses aren’t random. They are deeply wired into our biology, shaped by millions of years of evolution. To understand why we react the way we do under stress, we can look at two powerful frameworks: Polyvagal Theory and the Triune Brain Model.
The Triune Brain: Our Three-in-One Operating System
Neuroscientist Paul MacLean proposed the Triune Brain Model to explain the layered development of the human brain. While it's more of a metaphor than a precise anatomical model, it helps us understand the evolutionary roots of our behaviour.
Reptilian Brain (Brainstem)
The most ancient part of the brain, responsible for survival functions like heartbeat, breathing, and the freeze response. This brain keeps us alive, and it's all about automatic, instinctual reactions.Limbic System (Mammalian Brain)
This layer handles emotion, memories, and social bonding. It's the home of our fight or flight responses—activated when we perceive threat and need to react fast.Neocortex (Human Brain)
The most evolved part, responsible for reasoning, decision-making, language, and self-awareness. It allows us to reflect and plan—but often gets overridden when our survival system kicks in.
Polyvagal Theory: The Science of Feeling Safe
Enter Polyvagal Theory, developed by Dr. Stephen Porges. This theory builds on our understanding of the autonomic nervous system, particularly the vagus nerve, which is like a superhighway running from our brain to major organs.
Instead of a simple "on/off" switch for relaxation and stress, Polyvagal Theory suggests we have a hierarchy of response states, based on how safe or threatened we feel:
Ventral Vagal State (Social Engagement)
When we feel safe, our body supports calm, connection, and communication. We can think clearly, make eye contact, and regulate our emotions.Sympathetic State (Fight or Flight)
When danger is detected, we shift into a mobilized state—our heart races, muscles tense, and we prepare to fight or flee. This is often what people associate with anxiety, anger, or panic.Dorsal Vagal State (Freeze/Shutdown)
If fight or flight feels impossible or unsafe, our body may default to freeze. This is a protective shutdown: we might feel numb, disconnected, or paralyzed. It’s the body’s way of playing dead to survive.
How the Triune Brain and Polyvagal Theory Work Together
Polyvagal Theory helps us map these stress responses onto the triune brain:
Freeze (Dorsal Vagal) – rooted in the reptilian brain. When overwhelmed, we might collapse or dissociate, driven by primal survival wiring.
Fight or Flight (Sympathetic) – activated through the limbic system, which rapidly scans for threats and mobilizes us to respond.
Social Engagement (Ventral Vagal) – regulated by the neocortex and brainstem integration. This is our most evolved state, allowing empathy, curiosity, and connection.
Why This Matters
Understanding this system helps us recognize our reactions without shame or judgment. These responses aren’t flaws—they’re adaptations. But by becoming aware of them, we can also learn to regulate our nervous system and move toward safety and connection.
Therapies like somatic experiencing, mindfulness, and trauma-informed practices often use this knowledge to help people heal from trauma and reconnect with their bodies.
In Summary
The triune brain gives us a framework for understanding how our brain evolved.
Polyvagal Theory explains the body's response to threat based on the vagus nerve.
Together, they show why we fight, flee, or freeze, and how we can return to connection and calm.
When we understand that our nervous system is just trying to keep us safe, we can begin to respond to ourselves—and others—with greater compassion and care.
