Triune Brain

The Triune Brain: Unraveling the Complexity of the Human Mind

The concept of the triune brain, proposed by neuroscientist Paul D. MacLean in the 1960s, sheds light on the intricate workings of the human brain. MacLean theorized that our brain can be divided into three distinct layers, each responsible for different functions and behaviors. MacLean’s presentation of the brain in three distinct layer is overly simplistic. MacLean recognizes this, explaining that “one cannot say anything about such a complicated structure as the brain without indulging in oversimplification” (MacLean, 1973).

MacLean explains that humans “inherited the structure and organization of three basic types which, for simplification, I refer to as reptilian, old mammalian, and new mammalian” He adds that “these three basic brains show great differences in structure and chemistry. Yet all three must intermesh and function together as a triune brain” (MacLean, 1973).

MacLean compared the evolutionary development of the brain to that of a building to which developers later added wings and superstructure to the original structure. MacLean explains theorizes that the oldest part of the human brain is basically reptilian, “forming the matrix of the upper brainstem and comprising much of the reticular system, midbrain, and basal ganglia” (MacLean, 1973). The next area of the brain to form he refers to as the old mammalian, and the most recent addition is the new mammalian.

Key Definition:

The Triune Brain concept was first presented by Paul D. MacLean in the 1960s. It refers to a three layered evolutionary development of the human brain, with each layer retaining specific functions and behaviors relevant to its stage in the evolution.

Lawrence Heller, referring to the triune brain, wrote that “newer brain structures that perform more adaptive functions were built on older structures, keeping those areas that had proved useful and slowly adding complexity and sophistication. The human brain and nervous system thus retain features of our reptile, mammal, and primate ancestors” (Heller and LaPierre, Kindle location: 1,611).

Leonard Mldinow, PhD. explains that “We humans also perform many automatic, unconscious behaviors. We tend to be unaware of them, however, because the interplay between our conscious and our unconscious minds is so complex. This complexity has its roots in the physiology of our brains. As mammals, we have new layers of cortex built upon the base of our more primitive reptilian brains; and as humans, we have yet more cerebral matter built upon those. We have an unconscious mind and, superimposed upon it, a conscious brain” (Mldinow, 2013 Kindle 173

The Three Distinct Layers of the Triune Brain

The Reptilian Brain: Our Primitive Core

At the deepest level of the triune brain model lies the reptilian brain, also known as the basal ganglia. This ancient part of our brain has been preserved throughout evolution and is primarily concerned with our survival instincts. It controls essential functions such as breathing, heart rate, and reproduction. This layer of the brain “coordinates the functioning of the heart and lungs and also the endocrine and immune systems, ensuring that these basic life-sustaining systems are maintained within the relatively stable internal balance known as homeostasis” (Van der Kolk, 2015, Kindle location: 1,083).

Bessel van der Kolk, a professor of psychiatry at Boston University School of Medicine and director of the National Complex Trauma Treatment Network, wrote that “the reptilian brain is responsible for all the things that newborn babies can do: eat, sleep, wake, cry, breathe; feel temperature, hunger, wetness, and pain; and rid the body of toxins by urinating and defecating” (Van der Kolk, 2015).

Habitual Behavior and the Reptilian Brain

The reptilian brain operates mainly on instinct and reflexes, triggering fight-or-flight responses when faced with danger. It is responsible for our basic survival instincts, territorial behaviors, and the formation of habits. MacLean suggests that Sigmund Freud’s concept of repetition compulsion may also be tied to the reptilian brain.

Our passion for habits is strongly rooted in our brains, explains Ada Lambert. She suggests that obsessive compulsive disorder originates in the reptilian brain. She adds, “compulsive behavior is an extreme dose of the basic principle, but the principle itself is correct, being healthy and wired in every brain. It enables orientation in the environment and the performance of routine actions of any animal, after it has learned the details relevant to its lifestyle. If it learned the path that leads to water, it will repeat it because the water is really there. Territoriality, the first passion of reptiles, is aided by their desire for routines. So are social behaviors, establishing status hierarchy, courtship dances, and any other everyday handling of survival missions in the minefield of life, by using the ‘correct’ secured path” (Lambert, 1997).

The Limbic System: The Old Mammalian Brain

Moving up the triune brain model, we encounter the limbic system. Scientists associate this mid-level brain structure with emotions, memory formation, and social behavior. It consists of various interconnected regions, including the hypothalamus, amygdala, and hippocampus. Van der Kolk describes the limbic systema as “the seat of the emotions, the monitor of danger, the judge of what is pleasurable or scary, the arbiter of what is or is not important for survival purposes.” And markedly, “it is also a central command post for coping with the challenges of living within our complex social networks” (Van der Kolk, 2015, Kindle location: 1,092).

Mldinow describes the limbic system as augmenting “the reflexive reptilian emotions and is important in the genesis of social behaviors” (Mldinow, 2013). And Heller describes that the functions of the limbic system as “uses pleasurable and unpleasurable stimuli to organize and guide how we respond to the events of our lives. The limbic system impacts the encoding of memory in that personally relevant and emotionally arousing events are more likely to be remembered” (Heller & La Pierre, 2012, Kindle location: 1,622).

MacLean explains that “the primitive cortex provides the animal a better means of viewing the environment and learning to survive” (1977).

We can see shadows of the psychological concepts of the hedonic principle (pleasure and pain) as well as behaviorism’s conditioning responses within this functions attributed to this layer of the triune brain.

Basically, the limbic system plays a vital role in processing and regulating emotions, such as fear, pleasure, and anger. It also contributes to our ability to form lasting memories and influences our social interactions and bonding with others.

The Neocortex: The Mammalian Brain

At the top of the triune brain model is the neocortex, the most recently evolved part of the brain. It is responsible for our higher cognitive functions, such as conscious thought, language, problem-solving, and abstract reasoning. This outer layer of the brain is what distinguishes humans from other animals, the foundation for complex mental processes.

We can further divide the neocortex into different regions, each specializing in specific tasks such as vision, auditory processing, and motor control. It is this part of the brain that enables us to analyze information, make informed decisions, and plan for the future.

The functions of the cortex creates acts as an executive with “the ability to strategize and plan long term in order to fine-tune the subcortical functions of the limbic system and brainstem” (Heller & LaPierre, 2012, Kindle location: 1,624). We attribute the ability to interpret, integrate, and create a narrative to the neocortex. Our cognitive functions give words to functions of all the layers of the brain.

The Interplay of the Triune Brain

Rather than operating independently, the triune brain structures work in concert, influencing our thoughts, emotions, and behaviors. The reptilian brain sets the foundation for survival instincts. The limbic system adds emotional color to our experiences. And the neocortex provides the intellectual capacity to reason and make informed choices.

We prefer to see ourselves as rational creatures dominated by the intellectual though attributed to the neocortex. We imagine that by pure strength of the new mammalian brain we can suppress the activity of the other regions.

Robert Sapolski, a professor of biology and neurology at Stanford University, asserts that the communication is less hierarchal. He wrote that “the limbic system talks to the cortex, rather than merely being reined in by it.” He continues, “in different circumstances the frontal cortex and limbic system stimulate or inhibit each other, collaborate and coordinate, or bicker and work at cross-purposes” (Sapolski, 2018, Kindle location: 544).

Mihaly Csikszentmihalyi wrote “we have learned that our vaunted reasoning ability is founded upon a thin overlay of tissue stretched over a solid reptilian brain, and we have come to suspect that when the interest of our blindly programmed genes comes into conflict with our values and even our self-interest, the genes win out” (Csikszentmihalyi, 2009, Kindle location: 451).

We have learned from modern technology that brain functions change under high stress conditions. During emergencies, our biological survival mode takes over, suppressing many of the functions attributed to the neocortex. The unconscious functions attributed to the two lower levels of the brain serve us better in some circumstances. The neocortex is like that bothersome colleague that shows up late to the meeting and then takes credit for the work.

Love and the Triune Brain

Human relationships provide an excellent example of the three functions of the brain working together or existing in conflict. The drive to procreate is part of the reptilian brain. Feelings of love belong to the midbrain or limbic system. And culturally appropriate relationship behaviors are monitored by the neocortex.

Lambert explains that “the reptilian brain supervises everyday routines, and we would not find our way around without it. The limbic system enables us to feel, to evaluate good and bad, and to love. This region enables loving motherhood.” The cortex doesn’t destroy these foundational functions of human survival. Hopefully, in a well functioning person, the intellect adds to our ability to love and be loved.

Lambert describes love from the three different functions:

  • “The reptilian brain pushes humans towards a blunt and functionalist sexual connection, a coming together of genitals rather than of hearts. This type of relationship involves much forcefulness and violence.” Domestic violence. obsessive compulsive throes of jealousy, and many other undesirable aspects of human connection begin here.
  • The limbic system creates the “excited, rutting love relationship in which hormones flood the brain stormily and enthusiastically, and cause feelings of bewilderment to the point of clouded consciousness and mindlessness.” This aspect of love is the foundation of love stories and stupidity.
  • The neocortex directs relationships in a more practical manner. It motivate the kind of behaviors “that makes marriage and family possible. It encourages a permanent, long-term bonding that gives preference to considerations of children’s welfare, finances, family, and social connections over hormonal excitement” (Lambert, 1997).

Current Brain Studies and the Triune Brain

While the triune brain model has provided valuable insights into understanding the human brain, it’s important to note that it simplifies the complexity of brain function. Modern research suggests that the brain’s architecture and functions are more interconnected and distributed than the triune brain model implies.

Error in Evolutionary Process

While the triune model provides an excellent division of different drives and functions, it’s construction from an evolutionary standpoint is misguided. First, “the brain did not evolve in successive stages” with “newer brain structures being superimposed over and on top of ‘older’ brain structures.” Evolution is a functional development, not through layered structures. A recent peer reviewed article explains, “A more useful evolutionary theory of how the brain works needs to integrate accurate knowledge of brain structure and function. Adaptation, survival, and reproduction are at the heart of evolutionary theory, and independent brain networks have evolved to increase adaptation to be able to survive and reproduce” (Steffen, Hedges, & Matheson, 2022).

Lisa Feldman Barrett wrote, “natural selection did not aim itself toward us—we’re just an interesting sort of animal with particular adaptations that helped us survive and reproduce in particular environments.”

Complex Interconnections

Barrett adds, “the triune brain idea is one of the most successful and widespread errors in all of science.” She adds, “the triune brain idea and its epic battle between emotion, instinct, and rationality is a modern myth” (Barrett, 2020). The heart of the error is that brain structures do not operate independently. “During emotional responses, there is activity in the amygdala and in the limbic system, but there is also activity in the cortical areas and brainstem” (Steffen, Hedges, & Matheson, 2022).

Sapolski explains, “there really aren’t ‘centers’ in the brain ‘for’ particular behaviors.” He continues, “the circuitry connecting various limbic structures is immensely complex” (Sapolski, 2018). Instead of am evolution occurring in layers, there was a slow and simultaneous functional evolution of various brain areas that impacted all areas of the brain.

Nevertheless, by appreciating the triune brain model, we can gain a deeper understanding of our innate drives, emotional responses, and higher cognitive abilities. Our brains are remarkable and intricate, constantly shaping our thoughts, actions, and interactions with the world around us.

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Barrett, Lisa Feldman (2020) Seven and a Half Lessons About the Brain. Houghton Mifflin Harcourt.

Csikszentmihalyi, Mihaly (2009). The Evolving Self: Psychology for the Third Millennium. HarperCollins e-books; Reprint edition.

Heller, Lawrence; LaPierre, Aline (2012). Healing Developmental Trauma: How Early Trauma Affects Self-Regulation, Self-Image, and the Capacity for Relationship. North Atlantic Books; 1st edition.

Lambert, Ada (1997). Evolution of Love, The (Human Evolution, Behavior, and Intelligence). Praeger.

MacLean, Paul D. (1973). A Triune Concept of the Brain and Behaviour. ‎Published for the Ontario Mental Health Foundation by University of Toronto Press.

MacLean, Paul D. (1977). The Triune Brain in Conflict. Psychotherapy and Psychosomatics, 28(1-4), 207-220. DOI: 10.1159/000287065

Mlodinow, Leonard (2013). Subliminal: How Your Unconscious Mind Rules Your Behavior. Vintage; Illustrated edition.

Sapolski, Robert (2018). Behave: The Biology of Humans at Our Best and Worst. Penguin Books; Illustrated edition.

Steffen, P., Hedges, D., & Matheson, R. (2022). The Brain Is Adaptive Not Triune: How the Brain Responds to Threat, Challenge, and Change. Frontiers in Psychiatry, 13. DOI: 10.3389/fpsyt.2022.802606

Van der Kolk, Bessel (2015). The Body Keeps the Score: Brain, Mind, and Body in the Healing of Trauma. Penguin Books; Illustrated edition.

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