Why do so many people keep repeating that we have three brains?

I recently received an email from a student - from a university other than where I work - asking for my collaboration to validate an instrument of his degree work. The student proposed “to describe the degree of influence and persuasion that can be generated to a certain group of civilians, from advertisements built based on portray a certain stimulus in the mind of the consumer. Basically create responses and behaviors, from an audiovisual product that addresses any of the three brains of the human being (cortex, limbic and reptilian) ”(my italics).

I diplomatically declined, but his conception of the neuromarketing I found it so distorted that I felt compelled to write about it. triune brain, a concept that has become terribly contagious in the minds of many people, even in academia. And it is not the first time I do it: I had already questioned it in an article for the magazine Earring (Carvajal, 2018) where he analyzed the myths propagated by the triune brain model in the educational field.

The Dragons of Eden by scientist Carl Sagan (1980)

I first read about the triune brain in The Dragons of Eden, a book by the famous scientific popularizer Carl Sagan (1980) who recounts the experiments carried out by the doctor and neuroscientist Paul MacLean with various animals, including marmosets, from which certain brain regions had been removed with the consequent behavioral change, which led MacLean to suppose the existence of brain structures with functional specificities in terms of behavior, in particular those that had to do with a sexual show that did not seek procreation but territorial domination, behaviors that were associated with deep structures located in the nuclei of the midbrain, what MacLean would call the R-complex or reptile.

The dragons of eden

The expression "triune brain" was introduced by Paul MacLean in 1969 in a series of three lectures, but these were not published until four years later (MacLean, 1973). Starting from the emotional theory of James Papez (1937) MacLean developed the concept of the "visceral" brain (MacLean, 1949) which he later renamed limbic system in 1952, suggesting new structures (hippocampus, amygdala, and cingulate gyrus) to those suggested by Papez. The expression "limbic" was inherited from Paul Broca, who used it in 1850 to refer to the rim-shaped part of the cerebral cortex (from the Latin limbus).

MacLean's (1990) theory was based on extensive comparative anatomy studies of the brains of animals as diverse as alligators and monkeys. The conceptual and intuitive appeal of this theory has made it persist in many textbooks, courses, and lectures on biological psychology (Farley, 2008).

The triune brain model.

MacLean's model of the triune brain of brain structure and evolution suggested examining ourselves and the world at large through "three very different mindsets," in two of which the faculty of speech is not involved. The three brains could be distinguished, both anatomically and functionally, and would contain "very disparate proportions of dopamine and cholinesterase" (Sagan, 1980: 74).

Triune brain

Showing the skepticism that characterized him all his life as a popularizer, scientist, Sagan (1980) already warned in his book that it would be simplistic to propose that the three brains have a strict separation of their functions, since "all brain structures are densely interconnected", so that the "intelligence" attributed to the reptilian complex, for example, when the marmoset displayed its genitalia to dominate its territory, also involves neural circuits activated in other structures for example, the limbic system and the cerebral cortices of both hemispheres.

Sagan He warned, when referring to the encephalic functions attributed to the triune brain model, that "it is not possible to speak of a strict separation of functions on pain of oversimplifying the matter." It is indisputable, Sagan said, that in man both ritual and emotional behavior are strongly influenced by abstract reasoning of neocortical origin. (Sagan, 1980: 101).

Why do we like models so much?

Models have been used routinely to help explain scientific concepts (Chittleborough and Treagust, 2009). They have been helpful in understanding the world: since ancient times, models have tried to explain reality. Examples of models are: en psychology, the tripartite soul of Plato and Aristotle and the Freudian model of the ego / it / superego; on chemistry, the atomic models of Democritus, Dalton, Bohr, Rutherford; on astrophysics, the models of the origin of the universe and a long etc.

In any field of knowledge, the mind seeks the simplest available interpretation of observations or, more precisely, balances a bias towards simplicity with a somewhat opposite restriction to choose models consistent with perceptual or cognitive observations (Feldman, 2016).  

Brain 1

Some Reasons the Triune Brain Model is Inaccurate

  1. The emotions they are not processed exclusively by the limbic system. The neocortex also performs emotional modulation functions in a feedback system with the amygdala (Rempel-Clower, 2007).
  2. The amygdala is not only involved in emotional processing; he has also been involved in activities cognitive superiors (Schaefer and Gray, 2007) as well as in other cognitive processes such as attention, representation of values and decision-making (Pessoa, 2010).
  3. The brainstem is not solely concerned with survival activities ("reptilian territoriality"); also fulfills functions related to perception, the cognition and the emotion (Nishijo et al., 2018) and with the maintenance of cognitive activities during old age (Mather and Harley, 2016).

In conclusion, it is important to understand that the triune brain model is a very simplified version of the brain and it is more accurate to understand it as an intricate interconnected network of neurons -whether from the cortex, the limbic system or the brainstem- that communicate, modulate and feed back each other, directly or indirectly. The only commendable thing about the triune brain model is that it has allowed people without any notion of neuroscience, approach this discipline and be interested in continuing to explore its secrets. My invitation goes to them to continue studying the latest discoveries about brain function, particularly those models that revolve around the most recent discoveries of the brain. Human Connectome Project.

Relevant programs:

Master in Neuromarketing

Master in Neuroleadership

Master in Neurosales


   Carvajal, R. (2018). Feasibility of the triune brain model in education. Earring. Digital Magazine of the Doctorate in Education of the Central University of Venezuela. 4(8): 11-35. http://saber.ucv.ve/ojs/index.php/rev_arete/article/view/15792

   Chittleborough GD, Treagust DF. (2009). Why Models are Advantageous to Learning Science, Chemistry Education, 20(1):12-17. https://doi.org/10.1016/S0187-893X(18)30003-X

   Farley P. (2008). A theory abandoned but still compelling. Yale Medicine Magazine. Available in: https://medicine.yale.edu/news/yale-medicine-magazine/a-theory-abandoned-but-still-compelling/

   Feldman J. (2016). The simplicity principle in perception and cognition. Wiley interdisciplinary reviews. Cognitive science7(5), 330–340. https://doi.org/10.1002/wcs.1406.

   MacLean PD, Kral VA. (1973). A Triune Concept of the Brain and Behavior. Including Psychology of memory and Sleep and dreaming; papers presented at Queen's University, Kingston, Ontario, February, 1969.

   MacLean PD. (1949). Psychosomatic disease and the visceral brain; recent developments bearing on the Papez theory of emotion. Psychosom Med. 1949 Nov-Dec; 11 (6): 338-53.

   MacLean, PD. (1990). The triune brain in evolution: role in paleocerebral functions. New York: Plenum.

   Mather M, Harley CW. (2016). The Locus Coeruleus: Essential for Maintaining Cognitive Function and the Aging Brain. Trends in cognitive sciences20(3), 214–226. https://doi.org/10.1016/j.tics.2016.01.001  

   Nishijo H, Rafal R, Tamietto M. (2018). Editorial: Limbic-Brainstem Roles in Perception, Cognition, Emotion, and Behavior. Front Neurosci. Jun 12; 12: 395. doi: 10.3389 / fnins.2018.00395.

   Papez JW (1937). A Proposed Mechanism Of Emotion. Arch NeurPsych. 38 (4): 725–743. doi: 10.1001 / archneurpsyc.1937.02260220069003

   Pessoa L. (2010). Emotion and cognition and the amygdala: from «what is it?» to «what's to be done?». Neuropsychology, 48 (12), 3416-3429. https://doi.org/10.1016/j.neuropsychologia.2010.06.038

   Rempel-Clower NL. (2007). Role of orbitofrontal cortex connections in emotion. Ann NY Acad Sci. Dec; 1121: 72-86. doi: 10.1196 / annals.1401.026.

   Sagan, C. (1980). The Dragons of Eden. Barcelona: Grijalbo.

   Schaefer A, Gray JR. (2007). A role for the human amygdala in higher cognition. Rev Neurosci.18 (5): 355-63. doi: 10.1515 / revneuro.2007.18.5.355.

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