The Triune Brain: Three Brains Attempting to Work as One

How the Evolution of the Human Brain has Led to the Existence of the Triune Brain

Louis Cozolino

When thinking about the general evolution of humans, we primarily compare ourselves to our chimp-like ancestors. But when it comes to the specific evolution of the human brain—which gives us the powers of thought, logic, imagination, empathy, and morality—we must share skull space with the ancient brain equipment that we’ve inherited from our mammalian and reptilian forebears over the past several million years.

Beneath our newer equipment are structures driven by primitive instincts, unconscious impulses, and primordial fears. American physician and neuroscientist Paul MacLean was the first to call this structure the “triune brain,” based on the concept that the reptilian, ancient mammalian, and modern human brains are attempting to coexist and cooperate.

The triune brain structure consists of three parts:

  • The reptilian brain, at the core, is responsible for arousal, homeostasis, and reproduction.

  • The paleomammalian (“old-mammal”) brain surrounding it is involved with learning, memory, and emotion.

  • The neomammalian (“new-mammal”) brain, required for conscious thought and self-awareness, sits atop the other two.

These triune brain parts roughly conform to the common distinction of brainstem, limbic system, and cortex.

MacLean suggested that our triune brain doesn’t necessarily work well because each of the three brains processes information in a distinctive manner and has a unique agenda. For example, the function of the reptilian brain, which drives our instinct and behaviors, retains a good deal of executive control over our actions, while only a small region of the cortex is capable of awareness and articulating its strategies.

This means that multiple levels of the triune brain often vie for dominance simultaneously and conflict with each other, without our conscious awareness—an idea that parallels Sigmund Freud’s conception of the relationship between the conscious and unconscious brain.

That so much neural processing occurs outside of conscious awareness, and that executive decisions at multiple levels can oppose one another, lay the groundwork for considerable inner conflict. To these evolutionary layers are added the complexities of two cerebral hemispheres, a variety of vertical networks integrating the layers of the brain, and the variations of brain organization resulting from gender, vagaries in development, and influences of the cultural environment.

In a visualization of the triune brain suggested by the British cultural philosopher and management consultant Charles Hampden-Turner, the human brain is an anachronistic menagerie, which confronts the psychotherapist with the challenge of treating a human, a horse, and a crocodile, all attempting to inhabit the same body.

Tags: brain science | add | brain parts | brain structure | limbic system | neuroscience | neuroscientist | psychotherapist | the human brain | therapist | Triune Brain | Unconscious brain

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Tuesday, July 11, 2017 7:17:24 AM | posted by Rhiannon Daniel
I've been thinking and researching a great deal over the past few years about how best to deliver counselling to people who are Asperger's or on the Autism Spectrum, after receiving quite a bit of feedback that mainstream counselling does not work for them mostly, so reading the description of the 'triple' brain really interested me. It's slightly different, but importantly, from the Freudian model of Id, Ego and Super Ego. Many practitioners would express predominance of left or right brain as very important when relating to a particular client. To me, left brain dominance obviously characterises a lot of what constitutes perception for people on the autism spectrum. But looking at the three brain model, whereas I have always regarded much of autism process as an asset (for example, exceptional I.Q or intellectual development, adherance to rationality and so forth) the three brain model as described does make me wonder if there are absences or diminished brain development in autism. One example is the third brain inclusion of 'self awareness', many people I am in regular contact with who are Aspergers struggle with this. I personally do not know exactly why it is extremely difficult to engage in process leading to self insight - a very good aim in mainstream therapy of course for neurotypical people, and, achievable - but being able to encourage focus on detail, logic, and the painful frustration of being unable to manage a constant 'flooding' of difficult emotions would, I'd guess, make inward turning techniques very difficult for 'Aspies'. I've noticed that not only does this particular type of brain fail to empathise, but it appears that the inability to pick up social and relational signals one on one might be the result of lack of ability to arrive at self awareness. I am not an academic of course, I am a practitioner, but this is worth thinking about. I've had a few people on the Spectrum through my practice, but this was a while back before I had experience of this phenomenon, nowadays if it's obvious, or the client has a diagnosis, I refer on. I don't believe a viable, foolproof system of therapy which requires mutual empathy at some level, works for people on the Spectrum and to offer counselling to them based on a neurotypical model is probably irresponsible. I know they like CBT, because their question to a therapist is: Why do you keep asking me how this feels when all I need to know is what to DO?

Monday, May 12, 2014 10:58:28 PM | posted by daisys
Excuse me, sir--Louis Cozolino is the person who speaks of the reptilian brain. Granted, he's trying to simplify something extremely complex, and we know reptiles learn from experience. Why have you said that this is my fault is something I can't make out.

Tuesday, January 7, 2014 8:33:13 PM | posted by henrys
Hi daisys. Where do you get the impression that the brainstem started with reptiles? Reptiles have a brainstem (hindbrain + midbrain) and a forebrain, and pretty well developed forebrains at that. So what you write does not make sense, or at least I can't make it out. Henry

Tuesday, December 17, 2013 6:15:58 PM | posted by Theodore A Hoppe
Human Cognitive Evolution: How the Modern Mind Came into Being - Merlin Donald

Tuesday, December 17, 2013 6:12:55 PM | posted by Theodore A Hoppe
Complex systems are often highly adaptive, so we need to identify this 'conflict' that needs to "craziness."
For whatever reason the triune brain is a model that has fallen out of favor with neuroscientists.
One of the unmentioned aspects of this brain model is the networks that tie everything together. Merlin W Donald has written about "distributed cognitive-cultural networks" in the brain. These can account for mental disorder in a social context. This seems to be where the 'conflicts arise.


Thursday, December 12, 2013 8:58:44 PM | posted by daisys
These three parts of the human brain didn't develop independently and then get shoved together. They developed one layer on top of another.
The brain stem developed first (in reptiles), the limbic system got added on and learned how to coordinate with the brain stem. The neo-cortex developed in relation two the first two and in humans became much larger and more complex. In any highly complex system there will be conflicts. Maybe that's why humans must deal with craziness.