The Triune Brain


The Triune Brain is a theory from the 60s that tried to model the organization of the brain.

It is technically inaccurate as an explanation for brain activity as neuroscience understands it but it remains one of very few good approximations of what is going on in our head.

It was nevertheless a major step from medieval thinking saying that Reason was in the head, Emotion in the heart and Instinct in the guts. It still feels that way, though.

Bill Williams, a psychology professor turned trader, came up with his own division of the Mind, Core-Right-Left, which sort of match the Reptilian-Limbic-Neocortex division of the Triune Brain and we combine them into Brain 1, 2 and 3 in this Blog. Please refer to The Divisions of the Mind Article for the various correspondences..

We may use the terms interchangeably in our articles when they apply best, so please refer to the article on the Division of the Mind and its charts when needed.

The Triune Brain division was based on anatomical observations of various animals.

  • Lizards and birds had only the Reptilian configuration
  • Early mammals had both Reptilian and Limbic system (also called Paleomammalian complex)
  • Higher mammals, including humans, had the Reptilian, Limbic and Neocortex (a.k.a. Neomammalian complex

But this delimitation is not cast in stone, various species have a little bit of all in various proportions. Yet higher mammals have the biggest Neocortex.

In this Blog we will stray away from the strict Triune Brain theory and adapt it for our own purpose.


About 800 millions years ago, living things grew in complexity and adopted a new structure to handle that new complexity. A digestive chamber fed muscles animated by nerve tissues which sent and processed signals. They were what we call animals.
That living structure continued to grow in complexity and what was nerve tissue started its own subdivision of labor, one part would carry information back and forth and another would process the said information. The brain was born.

That nerve blob evolved to higher complexity and is still in use today. It is in charge of all bodily functions and handles information at an incredible speed, about 3 million bits per second. It handles things like dosing insulin, regulating temperature, maintaining heart beat. That is what we call Brain 1.0 or Core or also Reptilian Brain.

Survival implies improvement. Rare are the examples of species who could survive changing environments without adaption. Therefore, Brain 1.0 eventually had to grow beyond its functions. Facing harm, Brain 1.0 would manage healing. A later version (1.1?) removed the body part from harm with what we call reflexes. Pain was the main information type.

Brain 2.0 came into existence by implementing a new approach, avoiding harm altogether as soon as it could be detected. That is what Fear does. As we all know, this device is also still fully active. Other emotions were added to Brain 2.0 arsenal of information handling. It went up to actually being able to handle information from another brain, through facial recognition and body language. Fear felt by another fellow human can be perceived from a distance. The speed and capacity of that brain set is unknown and deemed infinite. We call it Brain 2.0 or Limbic system or Right Brain.

Then came problem solving. The latest device Nature found to avoid harm before harm even materialize. That is what Brain 3.0 is doing. Most authors agree on the Neocortex being the center of these functions. We also call it the Left Brain. One of the major drawback of this brain is its poor capacity at handling information, a mere 16 bits of information per second. This part of the Mind is regarded by many as the utmost achievement in matter of higher evolution. But it is in fact only the most recent and like any newly released products, it is full of imperfections.

But let’s go back to what the Limbic system actually does. The concept of going away from harm using Fear as a trigger is introducing a new concept: Decision making. The Limbic system is the actual center of our Life and is of the utmost importance.

Limbic is the center of Emotions (Fear, Anger), Connection (Love/Body language/Facial Recognition) and Decision.

  • People with damage in the Limbic areas are unable to make a decision, they keep pondering all the options using their Neocortex.
  • People whose ability to connect has been impaired or poorly developed are pure logicians and can be classified somewhere in the Austistic spectrum.
  • People whose emotions are poorly synced can be either useless or dangerous. A Healthy balanced Limbic system is a requirement for a healthy mental life.

A poorly developed or under-performing Neocortex only makes you an idiot but nothing depriving you from a healthy happy life. A malfunctioning Reptilian complex will no let you live long if at all.

The three brains actually communicate with each other but the Limbic remains the Boss. It is fed information from the reptilians and the Neocortex, then reacts to the generated emotions and makes a decision.

The Neocortex is the only one we can act on voluntarily. It is the one we are conscious of. We can only observe the other two, usually through dreaming, intuition or in a transient state (in the zone).

The Neocortex can have an influence on the other two but more so on the Limbic to which it is more closely linked. The Reptilian is also in conversation with the Limbic.

The Neocortex (like the Reptilian) is consistently feeding information to the Limbic. But the Limbic/Reptilian relationship has been refined over millions of years whether the Limbic is still not filtering out properly what the Neocortex is providing.

  • Reptilian will provide real life information, like pain, hunger, low sugar levels, high level of sexual hormones, etc.
  • The Neocortex will provide information about abstract danger like social embarrassment and also solution to problems it churned about.
  • The Limbic cannot distinguish between the signals from Reptilian or Neocortex. Thus things like Fear of Criticism are treated as urgent matters as the Fear of physical harm.
  • Only Neorcortex can understand offensive language but passes the information as a threat the same way Reptilian will pass information about the sound of incoming danger.

The Neocortex is also the slowest of all three systems. Several million times slower than the others. It cannot handle all the information that is fed to the other two. So they pass only a filtered version.

So what we are conscious of is just a tiny fraction of what is going on.

None of these three brains is programmed to shut off. Limbic must stay alert and Reptilian would let you die if it took a minute off. The Neocortex was not supposed to be off either but its poor capacity requires periods of suspension so some clean up can be done in its information files. This what we call sleep.

We can summarize the brain/mind divisions as follow:

  • What keeps us alive happens in the Reptilian system.
  • What makes us alive happens in the Limbic system.
  • What makes us conscious we are alive happens in the Neocortex.