Triggers and the Triune Brain: Understanding Why We React Before We Think

What Are Triggers?

A trigger is anything—a sound, smell, image, tone of voice, situation, or sensation—that activates a traumatic memory or stress response in the body. When triggered, we suddenly find ourselves experiencing intense emotions, physical sensations, or behaviors that seem disproportionate to the present moment. Our heart races, our throat tightens, we feel an overwhelming urge to flee or fight, or we shut down completely. The intensity of our reaction doesn't match what's actually happening now because we're not truly responding to now—we're responding to then.

What makes triggers so confusing and distressing is that they often happen instantaneously, bypassing our conscious awareness. One moment we're fine, and the next we're flooded with anxiety, rage, shame, or numbness. We might not even understand why. A colleague's tone of voice sends us spiraling. A certain facial expression makes us want to disappear. A particular smell triggers panic. The reaction arrives before we can think about it, before we can talk ourselves down, before we can remind ourselves that we're safe.

This isn't a failure of willpower or emotional control. It's not weakness or overreaction. Understanding triggers requires understanding how our brain is structured.

The key lies in what's called the "triune brain"—a model that helps us understand why we react before we can think, and why sometimes thinking doesn't help at all.

The Triune Brain: Three Brains in One

The triune brain model, developed by neuroscientist Paul MacLean, describes the human brain as having three distinct parts that evolved at different times and serve different functions. While modern neuroscience has refined this model, it remains a powerful framework for understanding how trauma affects us. These three parts are: the reptilian brain (brainstem), the mammalian brain (limbic system), and the human brain (neocortex). Each operates with different priorities, different speeds, and different relationships to conscious awareness.

The Reptilian Brain (Brainstem): Survival First

The oldest and most primitive part of our brain, the reptilian brain or brainstem, is responsible for automatic bodily functions and immediate survival responses. This is where our heart rate, breathing, digestion, and sleep-wake cycles are regulated. It's also the home of our most fundamental survival responses: fight, flight, freeze, and fawn.

The reptilian brain operates entirely outside conscious awareness. It's fast—reacting in milliseconds—and it's binary: safe or unsafe, approach or avoid, act or shut down. It doesn't think, doesn't analyze, doesn't consider options. It simply reacts based on past programming. When this part of your brain detects danger, real or perceived, it initiates the stress response before you even know what's happening.

This is the part of your brain that makes you jump at a loud noise before you realize it was just a car backfiring. It's what pulls your hand away from a hot stove before you consciously register pain. And when you've experienced trauma, it's what gets activated by triggers, throwing your entire system into survival mode in situations that your thinking brain knows are safe.

The Mammalian Brain (Limbic System): Emotions and Memory

The limbic system, which evolved later, is the seat of emotion, motivation, and memory formation. Key structures here include the amygdala (our threat detector and emotional alarm system) and the hippocampus (which processes and stores memories, giving them context of time and place).

The hippocampus is crucial for understanding triggers because it's responsible for marking memories with context—the when, where, and "this is in the past" information. When trauma occurs, especially repeated or intense trauma, the hippocampus can become impaired or overwhelmed. Memories get stored without proper context, which is why triggered responses feel like the trauma is happening now rather than being safely in the past. Your body can't tell the difference between remembering a threat and experiencing one.

The limbic system is faster than conscious thought but slower than the reptilian brain. It operates largely below conscious awareness, though its effects—our emotions—certainly reach consciousness. When you feel an emotion, the limbic system has already been activated and made its assessment.

The Human Brain (Neocortex): Thinking and Reasoning

The neocortex, especially the prefrontal cortex, is the newest evolutionary addition and what we typically think of as our "thinking brain." This is where language, abstract reasoning, planning, decision-making, and self-awareness happen. It's what allows you to read these words, analyze your experience, understand concepts, and make deliberate choices.

The neocortex is sophisticated, flexible, and capable of complex thought. It can consider multiple perspectives, weigh options, imagine futures, and learn from mistakes. It's where we construct narratives about our experiences, develop insight, and make meaning. When we're regulated and within our window of tolerance, the prefrontal cortex stays online and helps modulate the more reactive parts of our brain.

How Triggers Bypass the Thinking Brain

Understanding the sequence of brain activation helps explain why triggers are so powerful and why we can't simply think our way out of them. When you encounter a trigger, here's what happens in your brain, all within fractions of a second:

Why Talk Therapy Alone Often Isn't Enough

Traditional talk therapy operates primarily at the level of the neocortex. We discuss our experiences, gain insight into patterns, develop cognitive strategies, and reshape our narratives. This work is valuable and necessary, but when it comes to triggers, we're trying to use the slowest, most vulnerable-to-stress part of our brain to manage reactions originating in the fastest, most primitive parts.

This is why someone can understand their triggers intellectually—"I know my partner isn't my father, I know that tone of voice doesn't mean I'm in danger"—but still have their body react as if they are in danger. The understanding lives in the neocortex, but the trigger response is initiated by the reptilian brain and limbic system, which don't speak the language of logic and reason.

Imagine trying to have a philosophical conversation with someone while they're drowning. They don't need insights about the nature of water—they need to get to safety first.

Similarly, when the reptilian brain and limbic system are activated, we don't need cognitive reframing—we need nervous system regulation.

This doesn't mean talk therapy is ineffective for trauma. It means that for trauma work to be complete, it needs to address all three levels of the brain. We need top-down approaches (talk therapy, cognitive work, meaning-making) and bottom-up approaches (somatic work, nervous system regulation, body-based interventions) working together.

Somatic therapy works directly with the reptilian brain and limbic system, meeting the trauma where it's stored—in the body, in automatic responses, in subcortical brain structures. By working with sensation, movement, and the completion of interrupted survival responses, we can update the primitive brain's threat detection system. We provide the experiential evidence—not just the cognitive understanding—that the danger has passed.

Working with Triggers: A Three-Brain Approach

Healing from triggers requires addressing all three levels of the brain. Each part needs something different, and effective trauma work knows how to speak to each level.

The Journey: From Reactive to Responsive

Healing from triggers isn't about never getting triggered again. Triggers may always produce some response—that's normal, that's your brain doing its job of keeping you safe. But the goal is to shift from being completely overtaken by the trigger to being able to recognize, regulate, and respond rather than simply react.

This journey looks like: noticing the early signs of activation before you're fully triggered, having tools that work at the level of the reptilian and limbic brain, returning to regulation more quickly when you do get activated, and gradually finding that the things that once triggered intense reactions now produce only mild responses.

As your nervous system heals, as the three parts of your brain learn to communicate better, as your reptilian brain's threat detection becomes more accurate rather than oversensitive, you'll notice profound changes. You'll be able to stay present in situations that once sent you fleeing. You'll feel emotions without being consumed by them. You'll have access to your thinking brain even when stressed. You'll trust that you can handle intensity without falling apart.

Self-Compassion in the Face of Triggers

Perhaps most importantly, understanding the triune brain allows us to meet our triggered responses with compassion rather than shame. When you understand that your reaction is coming from the most primitive part of your brain, operating at speeds faster than conscious thought, trying desperately to keep you alive based on past programming—it becomes easier to meet yourself with kindness.

You're not broken. You're not weak. You're not overreacting. Your brain is doing exactly what brains do when they've learned that certain situations are dangerous.

The fact that your neocortex knows the danger is past doesn't help because the neocortex isn't the part of your brain running the show when you're triggered.

Healing happens not through self-criticism or forcing yourself to "get over it," but through patiently working with all three levels of your brain. It happens through building safety at the level of the body and brainstem. Through reprocessing memories at the level of the limbic system. Through understanding and meaning-making at the level of the neocortex. Each part needs its own attention, its own language, its own timeline.

Be patient with yourself. Your reptilian brain and limbic system are protecting you the only way they know how, based on the information they have. As you provide new information—through somatic work, through safe relationships, through moments of regulation—they will gradually update their programming. The triggers will soften. Your window of tolerance will expand. You'll reclaim more and more of your life from the grip of the past.

Moving Forward with All Three Brains

Understanding triggers through the lens of the triune brain transforms how we approach healing. We stop expecting our thinking brain to control responses that originate in much more primitive structures. We stop shaming ourselves for reactions we couldn't consciously control. We recognize that complete healing requires interventions at all three levels.

If you're working with triggers, seek approaches that address the whole brain—somatic work for the brainstem, emotional processing for the limbic system, and talk therapy for the neocortex. Give yourself time and patience. Celebrate the small victories: the moment you noticed you were getting triggered before you were fully activated, the time you used a grounding technique and it actually helped, the conversation that once would have sent you spiraling but now you could navigate with only mild discomfort.

The journey requires all three brains, working in concert, each receiving what it needs to heal. And as they heal, you discover that triggers lose their power, that the present moment becomes truly present rather than haunted by the past, and that your brain—all three parts of it—can become a source of wisdom rather than a prison of reactivity.