© 2018 by Dr. Sam Pascoe

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Hijacking the Triune Brain

In the next several blogs, I hope to offer a hopefully helpful oversimplification of a very complex and only recently understood aspect of what it means to be human: the Tripartite (Three-Part) Brain.



In the 1970's, neuroscientist Paul MacLean popularized a way of looking at the human brain which he called the triune brain. MacLean noted that the human brain–clearly the most highly developed brain on the planet–is not simply a “bigger” brain than those found in other, more primitive animals. It is actually three fairly distinct organs. As our species evolved, the primitive brains found in reptiles did not just increase in mass and volume to become mammals’ brains.


Although it has changed somewhat over these millions of years, the reptilian brain has stayed pretty much as it was. Instead, as life evolved, a new layer, with different functions and capabilities, was added on top of it. This is called the limbic system or mid-brain. It is found in lower order mammals (dogs, horses, etc.). It is also called the mammalian brain. It is also sometimes referred to as the paleomammalian brain or “old mammal brain”--“old” because it has been around a long, long time. The current stage in human evolution came about with the addition of a third layer, the neomammalian (new mammal) brain. It is also called the cerebral cortex. This, third layer of brain is the seat of our higher functions, as will be explained below. It is a big part of what makes us humans.


Thus, on a purely biological level, we humans are actually three animals in one. This means that our reactions to even the most simple stimuli are quite complex. MacLean noted that “our three brains don’t necessarily communicate or work well together because of their differing ‘mentalities’ and the fact that only the neomammalian brain is capable of consciousness and verbal communication.”


When our three sibling brains get into a squabble inside our head, sorting it all out can create a kerfuffle. As one scholarly wag put it, when we try to heal our conscious and subconscious selves, “This conservation of our evolutionary history alongside our modern neural networks confronts the therapist with the challenge of simultaneously treating a human, a horse, and a crocodile.”


The Reptilian Brain

The Reptilian Brain (the amygdala) is the most primitive and, thus, the most powerfully compelling part of the brain. It has survived for millions of years and is the part of the brain we share with reptiles. Its main function is to keep us alive. It can only ask–and answer–a few basic questions: “Am I safe?” “Do I eat it or does it eat me?” To these important--indeed life or death--questions the amygdala only has three (or some say four) responses in its tool kit: Fight, Flight, Freeze (and/or Submit). The good news is that having such a short list of possible responses facilitates the sort of quick, life-saving actions that are called for in threatening situations. The bad news is that we live in a world that often demands more options and rewards more nuanced responses.


Studies show that when the amygdala is stimulated electrically, animals respond with aggression. And if the amygdala is removed, animals get very tame and no longer respond to things that would have caused rage before. But there is more to it than just anger: When the amygdala is removed, animals also become indifferent to stimuli that would have otherwise have caused fear and even sexual responses. We need our amydalae.


The amygdala has saved our lives–and preserved the species–many times. This is the part of the brain that hurriedly dumps adrenaline and other powerful chemicals (hormones) into our systems when we believe we are threatened. (The threat does not have to be real, only perceived. The reaction is the same.) These reactions are so powerful and quick that the rest of the brain–the more rational and highly developed parts–are left playing catch-up. They watch helplessly as your body and emotions--jacked up on hormones--react following patterns they have learned over the years. These reactions may or may not be appropriate or helpful to the current situation, but they erupt nonetheless.


This phenomenon has come to be called neural hijacking.


Happily, and of necessity, the neural pathways that lead to this part of the brain operate very quickly–they are the super highways of the nervous system. When danger threatens, you don’t want your brain to dither. Conversely, and sadly, the pathways that allow us to “come down” from the “high” of these chemical dumps are much slower. So, while we can get “up” in an instant, it takes much, much longer to get back “down.”


An Example of Neural Hijacking

You are sound asleep and you are awakened by a loud noise coming from your dark living room. Your senses are immediately at full volume. Your heart races. Your body is prepared to freeze, fight, or flee. Then, you realize it was only your cat knocking over a book you had propped next to your chair. It turns out there is no threat. Everything is fine. You and your family are safe.

Does your heart rate immediately return to normal? Do you quickly return to a state of restful sleep? Probably not. Your rational brain (neomammalian) has been hijacked and it will take it quite a while to convince your reptilian brain to stand down.


We will come back to this in due course, but for now it is enough to understand that the primitive, reptilian brain can either save your life or ruin your life depending on whether

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