Why is the brainstem sometimes called the reptilian brain?

Over time, certain evolutionary improvements have been implemented in the brain of human beings that have allowed us to adapt to the different changes that have been presented to us and this is one of the main reasons why we have survived as a species.

It is said that our brain is 3 times higher than that of primates and at the same time it is made up of different areas that over time have been incorporated one on top of the other throughout evolution.

In this way, it has been found that there are three types of brains, which are the following: the reptilian brain, the emotional brain or limbic brain and finally the rational brain or neocortex. 

In this article we are going to answer the question ‘’Why is the brainstem sometimes called the reptilian brain?’’ we will talk about what the reptilian brain is: parts and functions. In addition, we are going to let you know in detail what this type of brain consists of.

Why is the brainstem sometimes called the reptilian brain?

The phrase “reptilian brain” derives from the fact that a reptile’s brain is dominated by the brainstem and cerebellum, which control instinctual thinking and behavior for survival.

As we know, the brain has been in constant evolution over more than 250 million years and throughout this process, it has been acquiring new functions and increasingly complex abilities. The oldest brain, to which the limbic and neocortex have been added later, is the reptilian brain.

This brain was identified and developed through MacLean’s triune brain theory. The reptilian brain, also known as the R complex or reptilian complex, is the one we share with other mammals and reptiles.

It is mainly responsible for starting our most basic and primitive functions such as protecting us from possible threats, defending ourselves and fleeing to ensure our own survival. It is also in charge of carrying out some unconscious and involuntary behaviors such as our breathing, blood pressure, temperature, balance, among others.

The reptilian brain or reptilian complex occupies approximately 5% of our total brain mass.

Characteristics of the reptilian brain

This type of brain is not reflective and, on the contrary, acts unconsciously and instinctively.

As its main function is to take care of our own survival, it is considered that it is also in charge of making it difficult for us to achieve our personal goals since it feels safe only being in a known terrain, however when it enters unknown terrain, it feels extremely threatened and prefers to flee and escape before facing something new.

Parts of the reptilian brain

The reptilian brain is made up of the reticular system, the cerebellum, the basal ganglia, and the brain stem. Below we will briefly explain what each of these parts of the brain consists of:

Basal ganglia

These are neural structures that are connected to each other and are located deep within the cerebral cortex. The main function of the basal ganglia is to process information about our own body movement to adjust it to different situations and also carry out an appropriate act.

For example, when we want to drive a car, we have to carry out certain actions and body movements to do it correctly. So it also helps us to plan our actions to achieve some goal.

Reticular system

It is a set of neurons that are located in the brain, near the spinal cord. The main function of this system is to regulate the state of sleep and wakefulness.

It is also in charge of filtering the information that comes through the senses, choosing those data that are of interest to them and putting aside those that are irrelevant, which finally do not reach consciousness.


It is one of the oldest parts of our brain and it is located in the posterior fossa of the skull, as it is an extremely compact organ. The main function of the cerebellum is to maintain proper balance and muscle coordination.

Brain stem

It is located between what is left of the brain and the spinal cord. The brain stem, or also called the brain stem, is made up of 4 different areas that are connected to the diencephalon. The main task of the brain stem is to serve as a circulation pathway for almost all sensory pathways, with the exception of the olfactory and visual.

Functions of the reptilian brain according to psychology

Once we know what the reptilian brain and its parts are, it is important to know the functions of the reptilian brain.

The reptilian brain fulfills different functions in our daily life, then we are going to mention in more detail what they are exactly.

  • Survival. As we have seen previously, the main function of the reptilian brain is to keep us protected from any threat that may arise and also ensure our survival. 

Although it is undoubtedly an essential and extremely important function, sometimes, if we do not know how to control it, it can prevent us from achieving our vital goals and objectives when facing new situations. 

This is because it perceives new situations as possible threats and prefers to stay in the “safe area”.

  • Regulate basic vital functions. As we saw earlier, it is responsible for the regulation of our basic functions such as breathing and heart functions.
  • Avoid pain. It is responsible for seeking pleasure and all those sensations that are pleasant to the person.
  • Territorial behavior. It is one of our own survival instincts that makes us tend to defend our home and also take care of the people closest to us and our belongings.
  • Reproductive need. To ensure survival, the reptilian brain is responsible for activating our sexual instinct and motivation that causes us to attract other people.

Understanding the idea of ​​a triune brain

Paul MacLean’s idea of ​​the triple brain is based on the idea that the human brain inhabits 3 different brain systems, with their own operating logics, and that each of them has appeared in our evolutionary line in a sequential way, the one over the other.

This means, among other things, that these three brains would be relatively independent and that they would be related to each other following a hierarchy, depending on their age and the importance of their functions for our survival.

The reptilian complex, for example, being the first to appear, would be the structure that carries out the most basic and most important functions to survive in the here and now, while the neocortex, being the most recent structure in the evolutionary line that leads to Homo sapiens, would be the one in charge of the most refined and complex functions.

The logic that follows this conception of the human brain is very reminiscent of a way of understanding evolution as a process in which the new accumulates on top of the old, so that these two parts maintain relative independence from each other, although the two parts are affected.

It also reminds of the idea that the emotional and the rational are part of two diametrically opposed psychological dimensions and that where there is one, the other does not fit.

The Three Brains Model and Marketing

The idea that we have a reptilian brain, a limbic brain, and a rational brain has long seduced many people in the world of advertising, market research, and marketing.

The triunic model allows us to consider separately three areas of people’s psychological life that are very easy to learn and internalize: a rational instance, an emotional one, and an impulsive one.

This has meant that in recent decades the interest of advertising campaigns has focused on appealing to the reptilian and limbic brain, but not to the rational one: the reason is that, considering that these two are more rooted in our evolutionary history, they are easier to predict and, at the same time, produce more powerful purchasing needs, given their importance and their hierarchical position as pieces of the brain more important than the neocortex.

Advertisements and marketing campaigns have gone from thinking of the customer as an agent who needs to be informed about the characteristics of the product to rationally decide according to their interests, to try to touch a chord with people to sell them a sensation associated with the product, more than the product itself.

And the truth is that this change of approach is considered a great success; Unlike what happened in the 60s, today it is very common to try to seduce potential buyers without talking about the characteristics of the product or its price: emotions are simply evoked or stories easily associated with a lifestyle that we want to make our own.

Bypassing the logic of the rational brain and targeting basic emotions and desires is proving so profitable that even expensive products such as perfumes or cars are promoted in this way.

MacLean’s Theory in Neurosciences Today

However, beyond what happens in the business world, in neuroscience and in evolutionary biology, the model of the three brains is considered to be out of date, among other things, because it understands brain development as a process of construction by “pieces” that have been assembled one on top of the other and that carry out certain tasks by themselves.

Today the opposite is believed: that in the functioning of the brain, it is not so much the function that the parts of the brain perform by themselves as the way in which they connect to each other to work together and in real-time.

In addition, from what is known, evolution does not make new components integrate with the old ones, as is, without altering them.

Every time a mutation makes a trait generalize, it alters the functioning of the organism as a whole and the way in which the parts that had evolved before work, it is not limited to “expanding” capacities.

That is why the idea that brain organs “in charge of the rational” are coupled on the previous ones has not been well accepted.

In addition, the functions that each of the three brains were supposed to carry out well define the characteristic behavior of groups of animals that, according to him, represent the moment of evolution in which these structures appeared.

On the other hand, today we know that the basal ganglia (which would be part of the reptilian brain) do not have to do with the execution of genetically programmed actions, but are associated with the performance of voluntary movements that, after having been widely practiced, They have become automatic, such as cycling.

FAQS: Why is the brainstem sometimes called the reptilian brain?

What does reptilian brain mean?

The phrase “reptilian brain” derives from the fact that a reptile’s brain is dominated by the brainstem and cerebellum, which control instinctual thinking and behavior for survival.

Is the brainstem considered the reptilian brain?

Yes, the brainstem is considered the reptilian brain.

How are human brains different from reptile brains?

Humans have a much larger and rougher cerebral cortex than other animals of the same size.

How do you get over a reptilian brain?

It is true that biology has a very strong presence and that the natural tendency does not lead to risk. Staying in the famous “comfort zone” fixes nothing.

From here I encourage you to gain confidence in your own talents through commitment:

  • Commit to yourself
  • Commit to bringing the idea to market no matter what.
  • Commit to society

What triggers your reptilian brain?

The reptilian brain: It is focused on itself, that is, everything that is not for it, does not pay attention to it. … It is visual, therefore, everything visual immediately reaches the brain and activates decision-making. Responds to emotions, which can change decision-making.

In this article we answered the question ‘’Why is the brainstem sometimes called the reptilian brain?’’ we talked about what the reptilian brain is: parts and functions. In addition, we detailed what this type of brain consists of.

If you have any questions or comments please let us know!


Smith, CU (2010) The triune brain in antiquity: Plato, Aristotle, Erasistratus. J Hist Neurosci 19 (1): 1–14.

Naumann, R. K., Ondracek, J. M., Reiter, S., Shein-Idelson, M., Tosches, M. A., Yamawaki, T. M., & Laurent, G. (2015). The reptilian brain. Current Biology, 25(8), R317-R321.