The triune brain theory was proposed by Paul MacLean in the mid 20th century well before sophisticated brain imaging technology.
In her book 7 ½ Lessons About the Brain, Lisa Feldman Barrett describes that “The triune brain idea is one of the most successful and widespread errors in all science.”
MacLean’s Triune Brain theory advocated that the human brain evolved in three distinct stages into three layers, the reptilian, mammalian, and rational mind. MacLean believed that The brain stem and cerebellum constituted the “reptilian brain” that was responsible for survival and primal instincts. He believed it was the most ancient in terms of evolution and is sometimes referred to as the lizard brain.
The second evolutionary layer of the brain he described as the “mammalian brain” or more specifically, the paleomammalian cortex. He argued that it was comprised of the Limbic System, which includes the amygdala and hippocampus. His theory was that the limbic system comprised the “emotional mind” and was the seat of our emotions.
The neocortex MacLean referred to as the “rational mind.” Or more specifically the neomammalian cortex. He believed it was the last layer to evolve and was the seat of language, planning, and abstract thought.
Today, most neuroscientists agree that compartmentalizing the brain into three distinct layers with functions that are relatively isolated from one another is not correct. Lisa Feldman Barrett is firm in advocating that “You have one brain, not three.”
As our knowledge of the brain progresses, some educators, including theologians have turned away from discredited ideas like the triune brain theory.
One example is how James Ashbrook and Carol Rausch Albright’s 1997 book The Humanizing Brain drew heavily from the triune brain theory and even dedicated to Paul MacLean. Carol Rausch Albright’s more recent 2017 Interactive World, Interactive God has no mention of the triune brain theory or Paul Maclean.
As brain science continues to evolve and expand, some of the ideas that we hold today are certain to be refined or discarded in the future. Pioneers within any field are bound to be wrong on occasion. Being humble to admit our mistakes can help us discover more meaning and more truth.
Dan Siegel, who developed the hand model of the brain, notes that “although the old three-part model of the brain is no longer considered complete or accurate, it does provide a useful initial way of diving into the anatomy of the brain if the model’s limitations are acknowledged from the outset” (Siegel, The Developing Mind, 36).
For a more thorough assessment of triune brain theory’s disuse, see Barrett, 7 ½ Lessons About the Brain, 2020; See also Gazzaniga, Ivry, and Mangun, Cognitive Neuroscience, 2018; Dan Siegel, who developed the hand model of the brain, notes that “although the old three-part model of the brain is no longer considered complete or accurate, it does provide a useful initial way of diving into the anatomy of the brain if the model’s limitations are acknowledged from the outset” in Siegel, The Developing Mind, 36.