The Triune Brain Problem

The Triune Brain is a model of human consciousness developed by neuroscientist Paul MacLeon in the 1960’s. It simplifies the brain’s structure into a model with three independently conscious layers, arranged in order of complexity. According to the theory, human behavior is the result of these three layers competing to have their thoughts expressed and urges followed:

• The neocortex, or the “neomammalian” brain, handles rational, strategic, executive, and abstract thought.
• The limbic system, or the “paleomammalian” brain, is responsible for emotions such as joy, hunger, sadness, anger, etc.
• The brain stem, or the “reptilian” brain, runs autonomous functions, such as breathing and survival.

The Triune Brain theory tries to decode human behaviors according to how each layer influences decisions. Someone’s irritability when they’re hungry or frustrated could be the limbic system taking over. If someone is acting aggressively territorial, they are acting out of their brain stem. Rational thought, according to the theory, comes from the “human” part of the brain.

Critiques

The Triune Brain sounds correct both in how it decodes behavior and the scientific foundation it comes from. But the brain isn’t really “triune”, or 3 independent brains in one. Dr. Lisa Barrett summarizes in the following interview how the Triune Brain was disproven not long after its creation, in the 70’s. Once scientists could trace genetics, they learned the brain didn’t actually develop in evolutionary jumps from reptile, to mammal, and finally to humans. Most animals with spines, such as mammals, reptiles, birds, and even some fish, have similar triune, or three-in-one, brain structures that evolved in separate branches of the evolutionary tree. What actually sets human brains apart from other animals’ isn’t the size or complexity, but how long ours take to develop.

Therapists treat patients based on observed symptoms and external behaviors as defined by the DSM. The way the psychology diverges from neuroscience influences an ideology of control for patients to adopt. In their research article, Your Brain is Not an Onion With a Tiny Reptile Inside, Cesario, Johnson, and Eisthen (2020) present the impact of the Triune Brain as a behavioral therapy narrative: the conflict between “good” human rationality and animalistic urges. “Older” layers of the brain are given animal names, almost as a way to separate them from “higher” level, more advanced layers. Therapists can utilize the triune brain model to frame addictive or insecure struggles as primal urges to overcome or self delusions to ignore. Determination of where a patient is at comes from outside observations of their behavior by providers. This language is not only literally dehumanizing, it’s also invalidating and further pathogizes patients — people who don’t “win” get left behind.

Cesario, Johnson, and Eisthen (2020) demonstrate how the moralistic ideals of the Triune Brian limit the scope of research, perspective, and therefore healing. They lament the lasting impact of continuing to teach the model to psychology students:

“A more practical question concerns the benefits to psychological science if psychologists changed their mistaken views of neural evolution. Consider the consequence of believing that humans have unique neural structures that endow us with unique cognitive functions. This belief encourages researchers to provide species-specific explanations when it might be more appropriate to recognize cross-species connections. In other words, by anointing certain brain regions and functions as special, researchers treat them as special in their research.”

That chauvinistic perspective is a bias that limits research on healing modalities and bleeds into cultural and media understandings of trauma recovery.

Reclaiming the Narrative: Control vs Curiosity

As a teenager dealing with anger issues and meltdowns, therapy just reinforced their social stigmas. Therapists emphasized discipline with little guidance on how to actually sit and process feelings. So, I learned to deal with emotions the way I had dealt with spankings: smothering my memories in shame. My problems became invisible to a mental health system of emotional control. I just got better at hiding behind good behavior.

“Numb is a feeling too,” my first trauma-aware therapist often reminded me, decades later. Rather than prescribing behavior control though, our sessions focused on the lack of agency I had as a young child. Traumatic experiences had overwhelmed my prepubescent brain. In realizing how limited my choices were back then, my neglected inner child felt a little compassion.

That reframing helped me transmute my shame into curiosity. My emotional numbness reflected how deeply I had internalized control, suppressing my own agency. Compassion helped thaw that numbness – the internalized “freeze” in my nervous system. But it also left me very emotionally vulnerable.

I needed a behavioral model that was simple enough for my inner child to grasp and rooted in biology, not some ideology. Another doctor, a neuroscientist, used the triune brain to explain the body’s survival instincts. Despite the critiques, that foundation helped me reconnect with myself. If we understand models as tools, can we transform the triune brain into a tool for self discovery?

An Agentic Consciousness

The triune brain’s main flaw comes from Psychology’s outside-in perspective, through their focus on external, observable behaviors. While there are a lot of great ideas in Cognitive Behavioral Therapy, or even the DSM-5, they fall short when the patient’s traumas go beyond the therapist’s lived experiences. Traumatized patients can be easily gaslit and minimized in those environments because, on some level, everyone deals with anxiety, conflict, and rejection. It divides people into two camps: the ones that can control their emotions and the ones that don’t.

The triune brain worked for me because it became a toolkit to describe my own agentic consciousness. Inside-out instead of outside-in. Dropping old ideas, like ancient animal brains, doesn’t change how effectively it models the brain. To reclaim my agency, I needed to understand how my trauma, remnants of past survival reactions, still affects my entire nervous system.

Layer 0: The Nervous System

The nervous system is the body’s communication and command center, transmitting signals with the rest of the body. Signals communicate changes from your body: through the peripheral nervous system, to the central nervous system in the spine, and then up to the brain, which sends back responses. I like to think of consciousness, that internalized awareness in each person, as a projection that emerges from this spiral of activity.

Agency is the capacity to make your own decisions. Conscious agency is another way of saying free will, but not as a thing that you have or don’t have. It’s an abstract space measured by time. How long, between a stimulus and response, is spent in conscious thought?

In the peripheral and central nervous systems, reaction times are nearly instant and automatic. Like when the doctor taps your knee to test your reflexes. Response times increase as stimuli is processed through each layer of the triune brain. Each layer is a foundation for the next, processing the nervous system’s signals into new concepts for the rest of the brain.

Layer 1: Brain Stem

The brain stem runs instinctual, autonomic functions of the body: breathing, digestion, and survival. These operations are unconscious, meaning you have little agency over them. You don’t decide to start digesting food or forming a scab, those things just happen. You can only temporarily affect your breathing. Survival instincts subconsciously engage when they perceive uncertainty and danger. But if your nerves are settled, your agency has capacity for the next two layers.

Layer 2: Limbic System

With more agency, there is time and space for an internal narrative, a personality, even a creative flow state. The limbic system processes signals from the body into emotions such as joy, hunger, sadness, anger, etc. Agency here is limited to the present, but informed by the past. This is where you can learn from conflicts, empathize with others, access memories, etc.

Layer 3: Neocortex

Settled nerves and met needs form the best foundation to plan for the future. The neocortex has enough space for agency through intentional, rational, strategic, executive, and abstract thought.