The Triune Brain

How Evolution Relates to Trauma Symptoms

As a trauma therapist, I’ve worked with adults and children who have experienced trauma related to combat, sexual abuse, or accidents, as well as job related trauma for first responders. There are two key beliefs that some of my clients initially endorse: “I am broken because of what happened to me” and “I am weak because what happened to me still affects me”. Far too often these incorrect beliefs case trauma suffers to avoid sharing their pain with loved ones and/or getting the help they need.

By explaining the Triune Brain (pronounced try-yoon), I hope to help you learn how neither of those beliefs are true. Further, I hope you’ll learn that if you are having trauma symptoms, it is precisely because your brain and nervous system were working exactly like they are supposed to. The Triune Brain is a model of evolution of the brain and behavior, proposed by neuroscientist Paul D. MacLean in the 1960s. Since then, it has been researched and modified to the Adaptive Brain Model and has inspired various other theories of human behavior and therapeutic approaches such as Somatic Experiencing. For our purposes, we’ll keep it simple, using the Triune Brain model to explain why we react to trauma the way we do.    

Triune: Three-in-One

The Reptile/Primitive Brain

This is earliest brain that developed. It is connected to the nervous system that runs throughout the body. The first creatures to crawl out of the primordial swamp had the most basic brain function necessary for survival. These reptilian creatures needed efficient, hard-wired, automatic reflexes for when to fight, flee, or freeze. These brains managed basic survival functions like eat/drink, sleep, and procreate. These creatures hatched from eggs struggling for survival from their first breath to their last. They didn’t have or need parents because everything about them was reflexive and instinctive. They were built to survive stressful environments.    

The Mammalian Brain

As mammals evolved from reptiles, their more complex bodies required more complex brain functioning. So, another layer evolved on top of the reptile brain. Mammals are different from reptiles in many ways. They have significantly fewer offspring, and their offspring require significantly more time to grow and mature before becoming self-sufficient. This means they are more invested in their offspring. Mammals live in groups where they can enhance survival by sharing child rearing and hunting/foraging duties. The most notable upgrade to facilitate this more complex body and lifestyle is emotions. Emotions help mothers bond to their offspring and facilitate relationships. Emotions help navigate those relationships by informing when a group member is scared, hurt, lonely, sad, or happy. Naturally, this requires empathy. Through self-experienced emotions, a mammal can empathize with the experiences of another and respond appropriately. There are also additional hard-wired survival reflexes as well: crying out, fawning, and collapse. These new survival mechanisms help to survive stressful or abusive relationships (i.e. complex trauma).

The Human Brain: Neocortex or Cerebrum

This third layer of the brain brings thinking and experiencing the world to a whole new level. It gives us the capacity for mathematics to build cities and soar to Mars. We have reasoning, logic, language, and the capacity for creating music and art. We can study and manipulate our physical environment. One very important function it provides is the capacity for impulse control and to influence the other parts of the brain. Our human brain can consciously engage in relaxation techniques to calm the brain stem and nervous system when survival reflexes are triggered. It can work to regulate the difficult emotions the mammal brain is grappling with.   

What does this have to do with trauma?

Archaic Reflexes in a Modern World

We live in a much different world than that which we evolved from, but we still have those earlier layers of brain and their reflexive survival mechanisms. Now, rather than going into survival mode by the threat of a predator, we can feel threatened by the loss of a job or inability to pay the rent. While the threat to our survival isn’t immediately in front of us, we still feel that panic for survival.

Big T Trauma

 This is usually a single event that most would identify as traumatic such as a car crash, natural disaster, or accident involving threat to life or major injury. The person usually experiences extreme fear or horror and believes they will likely die or be seriously injured. These types of events most often trigger the reptilian survival reflexes (fight, flight, or freeze). Because we have efficient brains, the brain stores all the information associated with the experience (sights, smells, etc.,) for future reference and safety. When something familiar to the event is sensed, it evokes the memory. If the experience hasn’t been fully processed and integrated by the whole brain, it can trigger a survival reaction. This means trying to respond now the way we did then to get safe. Because the threat isn’t here, now, and the response is reptilian, it doesn’t seem to fit the situation that triggered it. This makes life very difficult for trauma survivors.  

 Little t Trauma

 These are usually events that aren’t life threatening but can have a major impact on a person such as bullying, emotionally abusive parenting, the death of a loved one, etc. When you look at it from the Mammal Brain point of view though, they can feel life threatening. Mammals that are bullied and shunned by the group are often cast out. A mammal that needs a group to survive feels very threatened by losing a social group, job, or loved one. The need to fit in and have relationships runs deep. These relational threats are not immediate but can feel imminent in these situations.

What this boils down to is when we are triggered, you can tell what part of the brain we are reacting from based on the reaction. If we try to fight, run, or freeze, our reptile brain kicked in. If our response is to cry out, fawn, or collapse, our mammal brain has reacted. In many cases, we are able to use our human brain to calm ourselves and remain in the here and now. But if the the reaction is significant enough, our human brains can go off-line because one of the lower brains has taken over. In other words, we are emotionally reactive and unable to access logic until the nervous systems calms down and the human brains comes back on-line.

I’d like to reiterate; the model of the Triune Brain has been updated and the current model is much more complicated than this. However, this model helps us understand the basic premise that we have adaptive brain functions from our evolutionary past that are still operating today. The interaction of these three brains can help us understand our responses to trauma and develop treatments to help us get unstuck when those events aren’t processed and integrated by our whole brain.

Sunny Street, M.Ed.

Licensed Clinical Mental Health Counselor, North Carolina       

Licensed Professional Counselor, South Carolina

Licensed Mental Health Counselor, Florida