The complexity of the human mind has meant that in trying to explain and understand how it works, hypotheses and theories have emerged from many different, sometimes even opposing, perspectives. This is not uncommon; in fact, it is part of the very essence of generating scientific knowledge.
After all, science is not the absolute and universal truth, but a very humble way of validating and testing explanations for how the world works, replacing them with those closer to reality when they are outdated.
However, this diversity of theories and hypotheses is particularly rich in the case of Psychology and Neuroscience, because what they are responsible for researching is subject to the influence of many variables. Thus, the mind can be approached from the study of behavior, which is neither palpable nor localizable in a specific area, or from the study of the body and, more specifically, of the brain. In the case of this last type of research, there is a hypothesis that has become very famous: that of the triune brain. According to this, where it would seem that the human being simply has a brain, there are actually three brains interacting with each other. Let’s see what it consists of and what is certain about it.
What is the Triune Brain Hypothesis?
The idea that we have three brains It was developed primarily by American neuroscientist Paul MacLean in the 1960s.. From his point of view, what appears to be the human brain is actually the superposition of three different brains, which show three qualitatively different stages in the evolution of our lineage.
It would be in the deepest part of the brain the reptilian brain, the most primitive of the three, whose characteristics are an adaptation to the way of life of reptiles, which appeared at a time when mammals did not yet exist. MacLean identified it with what are called the basal ganglia and their adjacent areas, a series of neural nuclei located in the deepest part of the brain, and proposed that this brain is responsible for triggering instinctive behaviors. : confrontation with competitors or attackers, the tendency to defend one’s own territory, mating rituals, etc.
Above the reptilian brain, the passage of time would have given rise to the paleomammary brain, emerged with mammalian reptiles or early mammals. This would include what is known as the limbic system and which is responsible for the emergence of emotions related to the motivation to feed, mate and associate with other individuals, as well as the parenthood. These are behaviors that rely less on pure impulses and do not translate into actions as predictable as those of the reptilian brain.
Finally, above the above would be the brain of the neomammal, which is found in the most evolved mammals, and in particular in primates. This would have given us the ability to reprocess information already processed by other parts of the nervous system, leading to more abstract thoughts and ultimately our ability to imagine complex experiences and predict future situations.
Do we really have three brains?
It is now considered that the idea of the three brains is, in any case, a simplification that must be understood. as a metaphorand not as a scientifically valid explanation or able to write in detail the reality of the functioning of our nervous system.
If it is true that the human brain is far from being a completely homogeneous anatomical structure (in fact, it is rather a set of organs), going so far as to consider that there are three physically separable brains and working in parallel is excessive. The nature of the brain causes different groups of nerve cells to perform specialized tasks, but at the same time, these constantly coordinate with each other constantly.
What happens in the human brain can be compared to what happens in an orchestra: different musicians specialize in specific instruments, but the ultimate goal is to offer a unitary experience: music, which cannot be understood in only analyzing its parts separately. . Therefore, today we know that a human being without neurological problems has only one brain.
On the other hand, it wouldn’t make sense for humans to have a reptilian brain, a paleomammary brain, and a neomammary brain. It is true that the evolution of species shows that there exist in today’s life forms “traces” or remnants of other life forms that belonged to ancestral stages of their lineage (for example, the sacred human bone, which includes the remains of a tail). However, what is kept must be functional, or at least not interfere too much with the chances of survival.
This means that although they sometimes remain vestigial organs that have lost their previous use, or are so atrophied that they are no longer of importance, or are modified so that they can play a new role. In the case of the reptilian or paleomammalian brain, it would not make sense to keep them as they are because it is not efficient to have several brains “competing” with each other to take control of the behavior; In any case, their anatomical characteristics would remain, but they would change their functional characteristics and take on new tasks and give up others.
The importance of ancestral brain structures
So the three-brain hypothesis doesn’t tell us anything? Not exactly, as a metaphor there are aspects that invite us to consider. For example, the concepts of “limbic brain” and “neocortex” are useful because they help us to know in which parts of the brain the processes most related to emotions and conscious reasoning and decision-making respectively take place, even if they are not entirely dedicated to these functions but cooperate with d other structures of the brain nervous system.
And it also lets us know that in our lineage, the tasks performed by the neocortex have not been as vital as those performed in the deeper areas of the brain, because expanding “outwards” to acquire new skill generates less risk than significantly modifying the rest of the brain. brain: brain structures that are already responsible for keeping us alive here and now.
The latter, in turn, reveals how emotions precede rationality. Virtually all of our actions have a number of affective and motivational elements behind them, but only in some of them is there a conscious decision to do something, or a medium or long term plan.
While no animal can afford not to have a part of the brain dedicated to triggering impulses and triggering emotions, only a few have been able to develop abstract thinking or even the ability to make physical tools ( like spears, arrows or hunting traps) or non-physical (like language). And, in fact, most of the decisions we make are not based on reflection, but on what we do spontaneously, according to how we feel, without thinking too much.
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- Barrett, L.F. (2020). You have one brain (not three). Seven and a half lessons on the brain. Boston: Houghton Mifflin Harcourt.
- Gardner, Russell; OnlineCory, Gerald A. (2002). The evolutionary neuroethology of Paul MacLean: convergences and frontiers. New York: Praeger.
- MacLean, Paul D. (1990). The evolving triune brain: role in paleocerebral functions. New York: plenary press.
- Nomura, T.; Kawaguchi, M.; Ono, K.; OnlineMurakami, Y. (2013). Reptiles: a new model for Brain Evo ‐ Devo Research. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution. 320 (2): 57–73.