©Arlene R. Taylor PhD    www.arlenetaylor.org

If the brain were so simple we could understand it,
we would be so simple we couldn't.
—Lyall Watson

articles200408“My teacher says the triune model of the human brain, described by Dr. Paul MacLean in the 1960s, is an oversimplification.” The young man’s chin was outthrust, his body language muscularly defiant. “What do you have to say?”

“To that I agree. In fact, one of the pluses of the model is its very simplicity, which in turn can be helpful due to its broad explanatory value. Your teacher’s comment reminds me of a favorite quote: If the brain were so simple we could understand it, we would be so simple we couldn’t.”

“So what’s the point in talking about it?” he persisted, albeit less belligerently.

“My brain’s opinion is that knowing something about brain function, even through the use of a simple metaphor, is better than not understanding even that much,” I replied. “Especially now that brain imaging techniques have provided a glimpse into clusters of brain structures that contribute key brain functions.”

“Like knowing what?” the young man asked.

“Like knowing that the cluster of brain structures associated with the neocortex (or new brain) is involved in high-level cognition and contributes to functions such as planning, modeling, simulation, and a sense of humor. Like knowing that structures associated with the limbic brain are involved with functions related to social and nurturing behaviors, mutual reciprocity, and memory. Like knowing that reptilian brain structures contribute basic functions that help keep you alive, involve territoriality, and that load and run ritualistic behaviors and motor sequences, including those that allow you to play computer games.”

That perked him up!

“But I thought that part of the brain was nonconscious,” he said.

“Good job,” I replied. “It is. Obviously you know something about the brain.” The young man smiled. “Although more has been learned about the brain in the last hundred years or so than was known in all the preceding eons, the information brush is still fairly broad.” Knowing he was an IT major, I added, “According to Caltech professor John Doyle, in the world of hardware and software, where everything is known about both systems, their functionality only exists by both realms interacting.  Yet, no one has captured how to describe that reality. That goes for the brain, too, in my book.”

3 layers“Okay, I’m in,” he said. “Lay the layers on me!”

cut awayLaughing, I clicked through a series of PowerPoint slides showing the three functional layers. They are combined in the drawing on the left and separated in the one on the right for easier viewing. Then I handed out a summary list of key components, explaining that each layer contributes distinct functions, although all layers interact at some level, as well.

1st Brain Layer

~Also known as the reptilian brain, R-complex, energy or sensory-motor brain

~Contains the brain stem, cerebellum, and connections to the spinal cord; it houses nonconscious functions


  • Tends to dominate when threat is perceived and safety or survival become top priorities and is usually the last portion of the brain to die
  • Registers awareness of the present, what’s happening right now
  • Takes in all sensory data, providing an awareness of the outer sensory world
  • Carries the “id-like” perception that “It’s all about me” and “I need to look out for me.”
  • Cells in the substantia nigra (part of the basal ganglia) secrete dopamine


  • Initiates fast protective survival reflexes/strategies in a perceived crisis situation
  • Houses automatic skills and/or ritualistic behaviors
  • Reacts to stressors automatically by initiating a stress response (e.g., fight-flight, tend-befriend, or conserve-withdraw)
  • In emergency situations alerts the neocortex to mobilize systems for defense
  • Able to help alter behavior, much as a chameleon changes color, depending on what it perceives is required or would be safer in a specific environment
  • Maintains functions critical to life (e.g., food/waste disposal, security, comfort)
  • Does not use language on its own but responds to language (and to the pictures created by what the brain hears and says and thinks) through an interpreter function in the neocortex
  • Houses the RAS (Reticular Activating System) that influences the brain’s position on the Extrovert-Ambivert-Introvert Continuum
  • Powers the brain’s electrical system (e.g., the brain runs on the approximate amount of energy required to power a 10-watt light bulb)
  • Routes incoming sensory data through the thalamus in the diencephalon
  • Compares command signals (intentions for movement) with sensory information (actual performance) and sends out corrective signals
  • Learns and performs rapid, highly skilled movements (e.g., keyboard playing, swimming, typing, running, speaking)

According to Joseph Chilton Pearce in his book The Biology of Transcendence (2002), this portion of the brain can take over the physical components of a learned skill, which frees the neocortex to observe and develop ways to improve performance. On its own, the reptilian layer is unable to alter inherited or learned patterns of behavior.

2nd Brain Layer

~Also known as the mammalian brain, relational brain, limbic system, and pain-pleasure center; it houses nonconscious functions

~Consists of a rim of cerebral cortex on the medial surface of each hemisphere and includes a collection of relatively small brain organs including these: two amygdala, mammillary bodies, cingulate gyrus (above the corpus callosum) the parahippocampal gyrus (in the temporal lobe below) and two hippocampi, which serve as the brain’s search engine


  • Perceives a sense of your internal world
  • Registers awareness of the present as well as the past
  • Carries the “ego-like” perception that “I am here” but “you are here, too, so my actions could impact you”
  • Is lightning fast, processing information an estimated 80,000 times faster than the neocortex (e.g., may trigger all phobias as well as crimes of passion)
  • Believed to be involved with all addictive behaviors via the dopamine pathways, which originate in cells of the substantia nigra in the 1st brain layer


  • Serves as the connection between the neocortex and the outside world
  • Maintains a balance between the neocortex and the reptilian brain, keeping the 1st layer from dominating the 3rd layer
  • Plays a role in a range of core emotions, having many direct connections to the right hemisphere of the 3rd brain layer but sparse connections to the left hemisphere
  • Provides the foundation for all relationships with its tools of emotion
  • Generates emotional impulses and plays a role in the processing and monitoring of emotion, both of which are essential for the process of remembering
  • Appears to be involved with managing associations, the building blocks of memory, helping transfer information from short-term to long-term memory
  • Processes the sense of smell directly, one synapse away from the nose
  • Searches the brain to collect pieces of information required in order to recall a memory--visual, auditory, or kinesthetic
  • Translates information from the neocortex into a language that can be perceived by the reptilian brain
  • Controls the immune system; hence, the profound effect emotions have on immune system functions
  • May be the most sensitive brain region to stressors; tends to rev up and run hotter in response to trauma (running hot is associated with a negative/depressive state of mind while running cool is associated with a positive empowering mindset)
  • Triages sensory stimuli via the thalamus and routes them to appropriate decoding centers in the neocortex

Dr. Paul MacLean's recognition of the limbic system as a major functional system in the brain eventually won wide acceptance among neuroscientists. The triune brain model is regarded by some as his most important contribution to the field, even though everything MacLean deduced hasn’t proved out as he envisioned it might.

3rd Brain Layer

~Also known as the cerebrum, gray matter, cortex or neocortex, and cognitive or    thinking brain; it houses both nonconscious and conscious functions

~Contains eight lobes, being divided by a natural fissure into two hemispheres that are in turn divided by natural fissures, resulting in four cerebral divisions 


  • Accounts for most of the tissue housed with the bony skull
  • Contains the potential for almost limitless translation abilities related to input from the outside and thought processes from the inside
  • Carries the superego-like perception, being able to direct good self-care and also to think about the good of others
  • Registers awareness of the present, past, and future
  • It contributes executive aspects of thought through the pre-frontal cortex (e.g., planning, goals-setting, paying attention, managing emotions, creating and moderating feelings, developing and using conscience, activating willpower, and learning societal rules related to morality, politics, and religion)


  • Generates conscious, cognitive thought processes, although only 5%-10% of what goes on in the brain may come to conscious awareness
  • Able to engage in very complex analysis using heard, written, gestured, and spoken language, including conveying information through laughter, and can process 125 bits of information and 40 bits of human speech per second
  • Carries a sense of reflection and connection that can extend beyond the concrete material world of bounded shapes (objects that have definable edges) into the world of imagination, creativity, and invention
  • Able to engage in abstract thinking (e.g., process information about objects that are not present in the environment; think about concepts not tied to bounded shapes) including the ability to fanaticize, imagine, innovate, and cogitate about “what if…”)
  • Creates active mental picturing (versus passive mental picturing of what another brain created that is activated when watching most TV programs, videos, and movies)
  • Anticipates and plans for the future; able to make changes as needed and often on the fly
  • Houses the mental faculty of humor, allowing for the development of skills related to what the brain perceives subjectively to be funny
  • Decodes sensory data (except for the sense of smell), being able to evaluate, monitor, moderate, and redirect sensory reports (e.g., provides a more measured/creative approach than that generated by the 1st brain layer on its own)
  • Contains an impulse toward novelty
  • Tries to make sense of information provided by molecules of emotion, the resulting conclusions becoming one’s feelings
  • Processes and stores information related to data that are important in society/culture (e.g., names, dates, numbers, labels) as well as data of value to the individual including data that contain emotional components
  • Able to analyze and evaluate two variables at a time and make a choice or decision about one over the other

That’s the triune brain in a nutshell. As an aside, Arthur Koestler made the concept of the triune brain the centerpiece of much of his work in The Ghost in the Machine, while English novelist Julian Barnes mentioned the triune brain in the foreword to his 1982 novel Before She Met Me.

“Good job; helpful information!” said the young man as he walked toward the door.

I figured that was high praise from his brain.