Reptilian brain: do we really have this ancestral structure?

The idea that we have a reptilian brain in the brain is widespread. Is it true?

The idea that human beings have a reptilian brain is widespread. This would be a vestige left to us by our cold-blooded, scaly ancestors who crawled on the ground, with a face that made few friends.

Lizards, snakes and turtles have been considered very primitive animals, which is why the oldest part of our brain, the most instinctive and simple, has been called the reptilian brain.

Is it true that we have a reptilian brain? Is it true that reptiles are as basic as they have been portrayed? Next we will see it.

Do we have a reptilian brain?

Outside the realm of psychology and academic neuroscience, the idea that humans, along with other mammals, have something like a reptilian brain is very popular and widespread. No, it is not that this conspiracy theory that says that there are lizard-like aliens among us is true, but the idea of the reptilian brain says that in our species we still conserve some structures that our sauropsid ancestors hadWe are also aware of the fact that the reptilian brain is a brain area responsible for a very basic, primitive and instinctive behavior.

We owe this idea to the physician and neuroscientist Paul MacLean (1913-2007) who proposed his theory of the triune brain, a model to explain the organization of the human brain. His theory tried to make sense of the existence of contradictory or, at least, alternative systems in our behavior that, through evolution, had been organized and coordinated in order to harmonize in the same organism.

This neuroscientist introduced his model in the sixties of the last century, although he developed it to its greatest extent in his book "The Triune Brain in Evolution" (1990). MacLean considered that in our skull there was not a single brain, but three brains, three brain structures that acted in the same way.three brain structures, each acting as an independent but interconnected Biological computer, which would have appeared throughout evolution as brain layers. Each of these brains would have its own intelligence, subjectivity, sense of time and also memory.

The three components of the triune brain would be the reptilian complex, the limbic system and the neocortex, appearing in the same order throughout evolutionary history. The most basic animal species from reptiles onwards would have only the reptilian complex, while as one moves up through the mammalian class the limbic system would be added and, upon reaching primates, the neocortex would be added, making the brains of humans and primates much more complex than those of reptiles.

1. The reptilian brain

The reptilian or R-complex brain is basically made up of the basal ganglia, the brainstem and the cerebellum, which are considered the most basic structures.These structures are considered to be the most basic in the model. The reason why this component is known as "reptilian brain" derives from the fact that the reptilian brain is dominated by the brainstem and the cerebellum.

According to proponents of the reptilian brain idea, this structure would be in charge of controlling instinctive behaviors and would focus on behaviors fundamental to survival, including aggression, territoriality, dominance and rituals.including aggression, territoriality, dominance and rituals.

The reptilian brain would be full of ancestral memories and would be in charge of autonomic or visceral functions such as breathing, heartbeat or vasomotor activity. It would also be involved in balance and muscle movement, being in charge of direct and reflex responses.

2. The limbic system

MacLean first introduced the term "limbic system" in a 1952 study, a term that would become widely used over time. The key parts of this second layer in the triune model would be the septum, the amygdala, the hypothalamus, the cingulate cortex and the hippocampus..

It is also known as the paleomammalian brain because it is considered the oldest proper mammalian part of the brain. This structure would be related to anything involving a more complex emotional response but also related to survival, being also involved in memory and social relationships, although it needs to interact with the neocortex to process emotions in their entirety.

The limbic system detects and avoids unpleasant sensations (e.g., pain) and seeks out pleasant sensations (e.g., pleasure). (e.g., pleasure), acquiring great importance in the motivation and emotions we feel when we satisfy physiological functions such as feeding or reproduction. It would also be behind parental behavior.

3. The neocortex

The neocortex or cerebral cortex is a structure that is only found in mammals, including humans, and is considered to be the most modern mammalian brain proper.. According to the model, the neocortex is the most characteristic part of the brain of the most evolved mammals, especially primates.

This structure is responsible for the execution of higher brain functions, encompassing cognition, sophisticated and precise motor control as well as sensory perception. The evolution of this structure in mammals is considered a key breakthrough that enabled humans to have cognitive functions such as language, reasoning, advanced thinking and intelligence.

The triune model considers that the human brain is the final result of a process of stratification of these three structuresIn other words, the reptilian brain, the limbic brain and the neocortex have been added throughout the history of evolution, forming a progressively more sophisticated brain and resulting in the brain of our species. The reptilian would be the deepest, most primitive and instinctive; the limbic would be the emotional component, involved in the motivation and care of offspring; and the neocortex would be the rational and modern brain, which allows us to use superior intellectual capacities.

Is this model true?

As we mentioned, the idea of the reptilian brain is widespread in popular culture, being assumed by many people. However, the truth is that the triune model is considered a myth. and although some aspects of the components mentioned in it make some sense, the truth is that no study has managed to separate emotions and rationality in a clear way, and the line that separates our survival instincts, emotions and cognitive aspects is not very well delimited.

MacLean's model has been largely discarded since the 2000s. The idea that evolution has been adding new and more complex structures for the sake of it is contrary to what evolutionary scientists know about the evolutionary process.. In reality, what has happened throughout evolution is that the brain has been reorganizing existing circuits, providing them with greater complexity and new functions. The appearance of new brain structures does not happen suddenly as if a new lobe grew out of nowhere; what has happened is that the old structures have been changing.

The idea of the triune brain, especially the reptilian brain, is rejected by most neuroscientists today, especially among those who have notions of comparative neuroanatomy. As proof we have the case of the basal ganglia, structures characteristic of the reptilian brain that can be found in mammals such as the lion. In this feline, the ganglia are proportionally larger than those found in the telencephalon of most reptiles..

Another aspect that dismantles the reptilian brain theory is that it is not only found in reptiles, but also in groups of vertebrates considered to predate the appearance of reptiles. An example of this are fish and amphibians, animals in which we also find the telencephalon, in this case made up of highly developed olfactory bulbs and a hindbrain.

Then we have the case of the limbic system structures. According to MacLean's model, this structure is properly mammalian but ancient, being in all mammals but not in reptiles, explaining why mammals are warmer and more sociable while reptiles are colder or emotionless. This idea is false, since other vertebrates have been found to show affection and interest for their offspring, as is the case of certain species of fish, birds and reptiles, such as crocodiles.

And finally we talk about the case of the neocortex. Although it is true that other vertebrates do not present this six-layered lamination structure, this does not mean that they do not have homologous regions, something like their own neocortexes functionally speaking. For example, the areas that make up the telencephalon of birds are connected to each other and perform functions similar to those reserved for the neocortex in the triune model. in the triune model.

Proof of this can be seen in the fact that, even in popular culture, it is known that there are very intelligent birds such as crows, capable of using sticks to get insects out of holes, putting stones in a beaker with water so that the water level rises and they can drink it, or even discriminate between different colors, associating some with food and others with the absence of food. In other words, they have memory, perception, learning ability and discrimination of stimuli.

In short, the idea of the reptilian brain is quite outdated. Reptiles are not as basic and simple as they are portrayed, nor do we have a purely reptilian brain that functions in a primitive way.. It is true that we have motivations associated with the instinctive, but rather than being due to the existence of three semi-independent brains, it is because we have a whole evolutionary history that has been preserving functions considered adequate for survival.

In addition, the bad reputation that reptiles have been given, considering them cold, unintelligent and lacking in emotions, completely dismantles the model. There are very intelligent, fast reptiles that display nurturing and affectionate behaviors. These animals, which are the only ones that we can say with absolute certainty possess a reptilian brain, are not as basic as MacLean originally called them. It is clear that the triune brain model, although popular, is still a myth and that what we humans have is a human brain.