You do not have a Reptilian Brain!

After coming across an endless amount of misinformation, disinformation, mythological lies, storytelling, and plenty of fantasizing in regards to the human brain’s supposed “reptilian” origin’s, I decided to share something from the brilliant neuroscientist and author, Dr Roger Douglas Fields PhD,  having recently read his very good book, Why We Snap.

From this book, Why We Snap, chapter 2, page 20-23, this is what Dr Fields has to say on how this particular terminology/meme came to be promoted then popularized and widely accepted as fact…

There is a beguiling popular notion that a “reptilian brain” lies at the core of the human brain. It’s cold, lizardly logic governs the most basic survival functions of life; among these are feeding, sexual behavior, and self-defense. Aggression, dominance, territoriality, and ritual displays are purportedly governed by this neural tissue, a vestige of our long-distant reptilian ancestors lurking inside us. The violent outbursts and unconscious reflex to attack or defend to the death are programmed by the automatic “doomsday” neural circuits in our “lizard brain.”

Layered on top of this primal lizard brain is purportedly an early-mammal brain. “If you imagine the lizard brain as a single-scoop ice cream cone, the way you make a mouse brain out of a lizard brain…[is] to put a second scoop on top of the first scoop,” writes neuroscientist David Linden in his excellent book The Accidental Mind. This second scoop of the neural ice-cream cone is is a more refined and complex gelato in contrast to the plain vanilla first scoop of the reptilian brain.

Superimposed on top of the second scoop is the modern primate brain. This is the superior outermost layer of neural tissue (neocortex) found in primates and to a lesser extent in other higher mammals. This cerebral mantle provides us with higher-level cognitive ability, abstraction, tool-making mastery, language, self-awareness, and the capacity to control the reptilian urges within ourselves and in our civilizations. This hot-fudge topping on the ice-cream cone (cerebral cortex) is what makes us human. An essential aspect of this “triune brain” theory is that these three brains compete with one another, explaining how someone can be overtaken suddenly by irrational impulses or rage. Those with weakened “mammalian brains” can commit acts of violence and crime propelled by unchecked primitive urges.

This colorful confection, however, is simply not true. You no more have a lizard brain curled up inside your skull than you have lizard scales armoring your skin. The popular idea of the triune brain originated back in the 1960’s, a period before the word “neuroscience” even existed. Our understanding of how the brain worked was abysmally primitive back when TV was just progressing from black-and-white pictures to color. The first neurobiology department in the country began at Harvard University in 1966. At that time anatomy, physiology, psychiatry, and neurology all dealt with brain function, but each was considered a different of science. The concept that brain science could be a separate and coherent scientific discipline distinct from all others was novel. Psychiatrist Dr Paul D MacLean conceived the triune brain theory based on little more than stitching together comparative anatomy and evolution into a Frankenstein scheme.

As a psychiatrist working at Yale University in the late 1940’s Paul MacLean had become interested in the brain’s control of emotion and behavior. Like Flynn and Hess before him, MacLean used electrodes to stimulate different parts of the brain in conscious animals to induce aggression and sexual arousal. Based on these experiments he pinpointed the center of emotion in the brain as the limbic system. The limbic system is located at the center of the brain and includes the hippocampus, amygdala and other structures. MacLean proposed that the limbic system had evolved to control the fight-or-flight response to danger and to react to emotionally pleasant and painful sensations. This is indeed one of the prime functions of the limbic system, but it also participates in several other functions.

In the 1960’s MacLean proposed that an even more primitive center, the reptilian brain, secluded at the core of the human brain, controlled the most basic bodily functions such as breathing. The lizard brain, he argued, resided in what anatomists term the brain stem, which is where the brain begins to swell from the top of the spinal cord inside the skull. These functions of the brain stem were never in doubt. The anatomy of the brain stem – that is, the connections leading into and out of it – and the immediate lethal result of damaging it, revealed it’s function vividly. But it was new to refer to this part of the human brain as the brain of a lizard.

MacLean proposed that the outermost layer of the brain, the neocortex, was the crowning achievement of evolution and thereby responsible for reasoning and all that is uniquely human. This is not a matter of scientific debate, but the idea that the human brain was formed by evolutionary accretion, beginning not with fish or amphibians but with the age of reptiles, bypassing birds, skipping to mammals, and then ascending to nonhuman primates and humans was a novel perspective. The human brain and mind, according to MacLean’s view, were revealed much like layers of past civilizations uncovered in an archeological  dig.

To neuroscientists the triune brain was nothing more than an attempt to conceptualize, simplify, and popularize some general aspects about the brain’s neuroanatomical framework, but nonscientific audiences and the media latched onto the concept of the triune brain as though it were a neurological truth, a Rosetta stone to understanding human behavior and emotion in terms of neural circuitry. Never mind that popularizers of the triune brain frequently managed to confuse what the three brain parts even were, most often referring to the “second brain layer” emotional limbic system in the human brain as the reptilian brain (brain stem) at the brain’s core that actually controls breathing and other automatic bodily functions. The pervasive error is seductive, because raging dinosaurs and angry crocodiles snapping into vicious attack are compelling allegorical images for primitive human emotions unleashed.

Still, the public and the media latched on to the concept, and the pseudoscientific assertion of the triune brain has entered into common usage and suffused our culture.

From Dexter, a TV series about a serial killer:

DEB: How do you know he’ll kill again?

DEXTER: An alarm is going off inside my lizard brain.

“The greatest language barrier,” MacLean wrote in a New York Times article in 1971, “lies between man and his animal brains; the neural machinery does not exist for intercommunication…”

Nothing could be further from reality. But it is easy to see how this mistake arises from the dramatic and complex aggressive behaviors that can be triggered by using an electrode to stimulate an appropriate spot in the brain. The problem here is that the question motivating the brain-stimulation experiments is itself faulty. A search made by probing electrodes into brain tissue carries a hidden assumption that there is such a cluster of neurons somewhere inside the brain that can overrule free will and take command of primitive human behaviors and emotions. But the fact that rage can be triggered by stimulating a particular spot in the brain does not necessarily lead to this conclusion any more than concluding that the power that propels automobile engine comes from it’s electric battery, you would be mistaken to conclude that the battery itself provides the automobile with the force to move. Delivering an electrical shock to a particular spot in the brain may simply tap into circuitry in a complex network that can span large areas of the brain that affect multiple systems necessary for the behavior.

The human brain is a unified, highly interconnected, complex system. It is distinct in countless ways from the brain of any other animal, just as the brain of each species has evolved independently through it’s own line of ancestry. New techniques and modern thinking recognize that brain function typically involves widespread communication through circuits spanning many different neural systems and regions of the brain. Some vital aspects of this circuitry may be more heavily concentrated in particular spots in the brain, but this does not necessarily mean that a particular brain region is “responsible” for generating the behavior that is evoked by stimulating it. As cognitive tasks become more complex, more areas of the brain become linked into operation to produce the behavior. In contrast to the lizard brain explanation for human rage, aggression and defense, the reality is a bit more complicated, and more interesting.


I hope this helps in clearing away some of the confusion surrounding this particular subject and that it can be of use to anyone who is searching for a truer understanding of our human brain.


Many thanks to Dr Roger Douglas Fields.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s