The Triune Brain: Three Brains, One Person

· September 24, 2018

The triune brain is a concept that neuroscientist Paul MacLean developed to refer to the three parts of the brain in human beings. These parts develop in different stages of the evolutionary cycle, which is why people say they’re created from the bottom up. This means that the oldest, most primitive part of the brain develops in the uterus. The emotional brain develops within the first 6 years of life. Hence, the prefrontal cortex develops last.

Advanced physics and technology have made neuroscience one of the most popular fields of research. Neuroscience has allowed us to better understand how the triune brain works (three types of brains in one). Now we’ll describe the characteristics of each part of the triune brain.

The reptilian brain

The reptilian brain is also known as the ancient animal brain or the reptilian complex. It’s located in the brain stem, right above the place where the spinal cord accesses the cranium. This is the most primitive part of human beings. It starts developing in the uterus, so it has an influence on everything newborns do (breathing, eating, sleeping, waking up, crying, urinating, defecating).

A mother caressing her sleeping baby.

The brain stem, along with the hypothalamus, controls the organism’s energy levels. This is called “homeostasis”. This term refers to the maintenance of internal balance. The functions that the reptilian brain controls are fundamental. However, we often disregard their importance when we think of the most advanced functions of our mind such as abstract thinking.

Many psychological problems are related to difficulties in the basic functions that the reptilian brain maintains. For example, for any trauma treatment, the specialist must take into account if the entire body has suffered an imbalance.


The emotional brain

The emotional brain or limbic area is located just above the reptilian brain in the center of the central nervous system (CNS). It stars developing from the moment the baby is born. The emotional brain or limbic system is constituted depending on the child’s experience, genetic composition, and temper.

Some authors also consider the emotional brain a mix of the reptilian brain and the limbic system. This is the center of our emotions and our danger monitor. 

Consequently, intense emotions activate the limbic system, specifically the amygdala. The amygdala is in charge of notifying us of possible dangers (as it’s the center of fear) and setting different responses in motion:

  • It triggers stress hormones.
  • Also, it releases nervous impulses.
  • Increases heart rate.
  • The amygdala increases oxygen consumption.
  • Prepares the body to fight or flee.

Through his studies with animals, Gray demonstrated that the lower the serotonin level, the greater the hyperactivity to stressful stimuli (and vice versa). For example, in male monkeys, he observed how the position in the dominance hierarchy influenced serotonin levels.

Certain people who have experienced traumatic events register the threat. However, their conscious mind continues as if nothing had ever happened. Although the mind can learn to ignore emotional messages from the brain, the body’s warning signals don’t. This means that the emotional brain will continue to function regardless. 

In addition, both parts of the triune brain (reptilian and emotional) are responsible for recording experiences and also managing our physiology and identification (comfort, security, threats, hunger, fatigue, desire, pleasure, pain).

The rational brain

This is the youngest part of the triune brain. It’s also known as the neocortex and it’s the one that differentiates us the most from other animals. This is where the prefrontal cortex is located, which is the one in charge of planning, anticipating, perceiving time and context, inhibiting inadequate actions, empathic comprehension, etc.

On many occasions, the rational brain can’t release the emotional brain only through knowing and understanding what happened to it (in the case of a trauma, for example). For a lot of people, it’s easier to tell what happened than realizing, feeling, and putting their internal experience into words.

Representation of the frontal lobe.

The frontal lobes are part of the rational brain. They’re in charge of balancing the person’s impulses and also their adequate behavior in a specific situation. A correct functioning of the frontal lobes is crucial to be able to carry out the following functions:

  • Maintain healthy relationships with other human beings.
  • Avoid doing things that would compromise us or that could hurt other people.
  • Regulate our impulses: hunger, sex drive, anger.

The rational brain occupies only 30% of cranial space and it basically manages our outside world. Understanding operations, reaching goals, managing time and sequencing actions are some of its main functions. Additionally, the cellular and biochemical organization of the neocortex of the rational brain is more complex to this organization in the emotional brain.