REPTILIAN BRAIN: THE THREE BRAINS THEORY - NEUROPSYCHOLOGY - 2024

The reptilian brain, also called the R complex, is the phylogenetically oldest area of ​​the brain, and is responsible for the most primitive and instinctive functions. Its main objective is to ensure the survival of oneself and the species.

The reptilian brain is located in the deep brain structures responsible for the most basic functions. It occupies 5% of our brain mass, and its main task is to react to environmental stimuli.

Yellow: Neocortex. Light orange: Medium brain. Dark orange: Reptilian brain.

It is not a reflective area, nor does it take into account the past or the future. Mainly, it implements fight or flight responses to face threats from the environment. It is also responsible for involuntary and unconscious behaviors, such as cardiac and respiratory functions.

Furthermore, it appears that our fear of change comes from the reptilian brain. Since, to ensure survival, it evaluates the known as safe and the unknown as dangerous.

The theory of the three brains or triune brain

One of the best known models to understand the complex structure of the brain was the theory of the three brains, triune or triune brain. It was developed by the American neuroscientist Paul MacLean from 1950.

MacLean's model attempts to describe the mammalian brain as a series of evolutionary breakthroughs.

From this perspective, the brain is essentially a reptilian brain to which two sections have later been added: the limbic system and the neocortex. This has involved a process of evolution of more than 250 million years, since mammals emerged with a different lineage.

So the development of the brain has taken place progressively, integrating increasingly complex functions. The most primitive functions continued to be processed by the same old structures.

Deep / old part

According to this theory the structure of the brain reflects the phases through which it has passed; states that deep in the brain is the phylogenetically oldest part. It is located in the brain stem, the one in charge of the most basic functions. They include the rhythms of life, heartbeat, and respiration.

In the depths of our skull is something similar to the brain of a crocodile: the R complex, which is "the seat of aggression, ritual, territoriality and social hierarchy."

Limbic system

Surrounding this structure is the limbic system. This system evolved from our mammalian ancestors, and is the source of our moods and emotions.

Cerebral cortex

On the outside is the cerebral cortex, which evolved from primate ancestors. It is here where the ideas, the inspirations are, where you read and write. In short, where conscious life is regulated, which differentiates man from other animals.

These three parts of the brain do not function independently. On the contrary, they are connected in multiple ways and influence each other.

The layers of the brain

The three brains evolved in the form of layers, as explained below:

Reptilian brain

Brainstem or brainstem

It is made up of the brain stem, the basal ganglia, the reticular system, and the cerebellum. As already indicated, it is concerned with ensuring our survival. It is the first filter by which we process the information.

Cerebellum

Through the reptilian brain we act in the face of threats, emitting an attack or flight response. Their functions are explained in more detail later.

Limbic brain

Limbic system

This brain arose in the first mammals. It allows us to memorize the answers to use them in future situations. It is made up of the thalamus, the amygdala (emotions), the hypothalamus, the olfactory bulbs, the septal region and the hippocampus (memory).

Tonsil (blue dot)

The limbic brain is a second filter, and it categorizes stimuli according to whether they cause pain or pleasure. Thus, when these emotions are experienced, the limbic brain will store them in memory and will generate approaching or fighting behaviors.

Hippocampus

It is the seat of value judgments that we sometimes make unconsciously, and that have a great influence on our behavior.

The cognitive-executive brain (neocortex)

This part is what differentiates us from the rest of the animals, since this brain allows us to consciously process information.

Here the higher intellectual processes are generated, such as social behaviors, empathy, inhibition, planning, logic, imagination, the processing of future experiences, etc.

Functions of the reptilian brain

The reptilian brain has been used by some authors as a concept to explain why we are often afraid, we resist changes, we are not very flexible or we only look for our survival.

The reptilian brain keeps us in a safe environment and away from danger, although it tends to be somewhat rigid and repetitive. It is the source of resistance to getting what we want. It is the reason why we are afraid and sometimes, rather than protecting ourselves, it prevents us from moving forward.

Apparently, the reptilian brain is associated with a series of functions that you can read below:

Basic vital functions

The reptilian brain seems to regulate those basic and unconscious functions such as blood pressure, respiration, body temperature, eye movements, balance or swallowing.

Automatic coping responses to environmental stimuli and challenges

Typical responses to danger, for example, are quick fighting reactions. Either on the run or on the search for a hiding place.

Thus, the reptilian survival instincts are attacks to protect their own life or to flee or hide. Humans can act like reptiles when faced with an unexpected stimulus that scares us, a threat or possible harm.

In fact, when faced with a stimulus such as a loud noise, our most immediate reaction is fright and paralysis. This is an example of the reptilian brain's mechanism to react quickly to potentially dangerous stimuli in the environment.

Basic emotions such as anger or aggression

Showing anger would be a manifestation of the reptilian brain, in which the individual tries to show that he is stronger than his enemy. Thus, it prevents the other from initiating an aggression, imposing respect and scaring them. It is a way to protect yourself or your loved ones from others.

Avoid pain and seek pleasure

Avoid pain and seek pleasure or pleasant sensations automatically. This also keeps us in a comfortable and safe environment.

The revenge

Faced with a conflict perceived as unfair, the reptilian brain may react by triggering a need for retaliation. Thus, it punishes others for actions or words that have hurt the individual before.

It is an instinctive behavior that can lead to conflicts and wars, when in reality the most adaptive thing would be to solve the problem in another way. That is, in a more reflective way and with the participation of cortical structures.

Territorial and tribal behavior

Our reptilian instincts lead us to increase our security through the defense and definition of the space in which we live. Because of this, one struggles to maintain and care for one's own home and belongings.

In addition, the reptilian brain ensures that we are in tune with the other members of our "tribe", avoiding showing behaviors or ideas that do not fit with those of that group.

Reproductive need

It is what leads us to be attracted to other people of our species with whom we have common qualities. This maintains the survival of the species.

Reptilian and striated brain

The reptilian brain is a name popularly given to an area of ​​the brain called the striatum. It belongs to the forebrain, and sends information mainly to the basal ganglia. At the same time, it receives information from the entire cerebral cortex, limbic system, and thalamus.

It is an older structure in the timeline of evolution. It seems that the establishment of connections between the striatum and the globe pallidus was decisive for the evolution from amphibians to reptiles. This helped the reptiles to adapt successfully to an entirely terrestrial habitat.

In this way, the pale balloon acts as a kind of filter before executing the action. Making the information that comes from more primitive structures processed before reacting.

The same happens in mammals, but at a higher level, since they use cortico-striated circuits. That is, first the sensory regions of the thalamus that capture the stimuli from the environment project towards cortical regions, which then innervate the striatum to act.

Thus, the information that comes from the environment goes through structures that process it, making sure that the best decision will be made. This is because an impulsive and involuntary response, typical of the "reptilian brain", is not always the best option.

Therefore, a participation of the cortex and its interaction with the reptilian brain, causes us to behave and think in a more flexible way.

In short, to make decisions, our neocortex interprets the information that comes from the reptilian brain and the limbic brain. Thus, it tries to inhibit impulses that are not adaptive and displays more appropriate behaviors for the situation.

References

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