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The Triune Brain in Evolution: Role in Paleocerebral Functions

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Paul D. MacLean has distinguished himself as a foremost figure in neuroscience. His early contributions to the understanding of the brain lie most notably in the area that he has named the limbic system. For the past thirty years, he has dedicated his research efforts at the NIMH Laboratory of Brain Evolution and Behavior, which he heads, to the promotion of his theory of the triune nature of the modern mammalian brain. His latest work, _The Triune Brain in Evolution: Role in Paleocerebral Functions_, is the paramount testament to that effort. The book is an impressive volume incorporating research from evolutionary biology, neuroscience, physiology, animal behavior, ethology, etc., into an insightful framework from which he draws many interesting, provocative conclusions, implications, and suppositions.

The triune theory has gained wide recognition, attention, and application in fields as diverse as psychiatry, education, and theology. However, neuroscientists have made little comment on the theory, pro or con, and, for the most part, have ignored it. Although chapters dedicated to the topic have appeared in a number of symposia, MacLean is usually the author. Since MacLean's peers, professional neuroscientists, have almost unequivocally declined comment, it thus becomes quite difficult for a novice to gain a critical view of the theory. In fact, since MacLean's review of the field is seemingly so complete, he is free to present the established thought on the evolution of the brain as he wishes. The novice is left only with his own efforts to sort things out.

It's amazed me how many times I have seen references to the "reptilian brain" within us by New Age thinkers and for-profit psychologists. The best of these referred back to MacLean as their source. Interestingly MacLean, as the respected neuroscientist that he is, gets things right that the pseudoscientists get wrong.

When Carl Sagan wrote Dragons of Eden in the eighties, he referred to the limbic system as reptilian. There were enough sources then on comparative neuroanatomy to be sure he was wrong. From the hippocampus on up the limbic system is purely mammalian, supporting the social life of a type of animal with heavy interpersonal needs, from mother and children to sometimes more than that. I was glad to see MacLean document this in greater detail than I could from sources in the eighties. MacLean sees the brain as three connected "analyzers", neomammalian neocortex, paleomammalian limbic system, and his "R-complex", which he mostly discusses as striatum, but includes the brainstem as well. As the reviewer from ten years ago pointed out this has not caught on with neuroscientists, who in my experience continue to call the brainstem "the brainstem". To call it reptilian is like calling our arms and legs reptilian. Mammals and reptiles are different everywhere, as MacLean points out. In labeling part of our brain "reptilian" MacLean is referring to the origin of the gross structure, but is also being metaphorical. We do not have an entire reptilian brain within us as some inner beast.

In the almost 600 pages of fine print text where he discusses this in terms of neuroanatomy and instinctive behavior, MacLean provides a treasury of information on reptiles, birds, and mammals. Anyone wishing data about how birds are more like reptiles than they are like mammals or how birds do as well as they do without our cerebral cortex would find much useful here. When MacLean gets to human behavior, comparing that to animal behavior, he covers many interesting topics. Human territoriality is one. Anyone interested in human behavior would be interested in such comparisons.

While MacLean is pointing to the idea of our being held hostage by our lower nature throughout the book, he only addresses this directly in his last chapter, where he wonders if, "... the R-complex `has a mind of its own'," and similarly for the limbic system. His reason for this, however, is simply the dependence of various behaviors on those areas being intact. He notes that this idea breaks from traditional neuroscience which sees "the reptilian brain" as controlled by the neocortex just as the spinal cord is.

There is truth in the points he makes regarding this, such as on p.578: "Moreover (and this cannot be overemphasized), the phenomenology of psychomotor epilepsy suggests that without a co-functioning limbic system, the neocortex lacks not only the requisite neural substrate for a sense of self, of reality, and the memory of ongoing experience, but also a feeling of conviction as to what is true or false." Yet if true, this is only true if one's limbic system is nonfunctioning, something that never happens in the absence of serious disease. MacLean goes on to be negative about how our convictions as to what is true or false are dependent on the nonverbal limbic system, "primitive, illiterate mind" that it is, but this is the same mistake. When the limbic system is connected to the neocortex, it becomes verbal. We don't have 3 separate analyzers. We have one very connected brain. Having a large enough stroke in any of these analyzers leaves us very bad off. We need everything we are.

People hear about brain areas in conflict, and they naturally attach it to what must be an age-old observation of conflict within our consciousness, between feelings and thoughts, or otherwise. Yet such conflicts in my experience are between parts of me that both can talk. I might feel that one side of the conflict is more me than the other, but often that changes over time. I'm guessing, but my guess is these conflicts are played out over my entire brain, not one part vs. another. There is nothing in this book that is evidence against that.

For anyone interested in either the science or the speculation here, this is a valuable book, but the overall message is not something that should be taken at face value.

Although virtually unrecognized Paul D. Maclean is one of the most important minds of all human history. This work details the evolution of the brain with an essential focus on "epistemic" perspective of understanding cerebral function. His insight into the importance of "play" in the evolution of the neocortex if ever understood by mainstream science will revolutionize every aspect of human culture.

This is one of the most important books in the recent history of neurosciences.
It is unique book in so many ways.
It a pure genius in terms of scientific observation and thinking.
It is a life time hard work and commitment to discover a new territory of science never been discovered before.
It is futuristic visionary book which undoubtedly will influence the future of science for decades to come.
It a history book through which one can see how science is made and how true scientists develop.
The subject of the book is so rich, its implications in neurosciences and philosophy are enormous.

However MacLean has made one little mistake; he is born will ahead of his time. The world needs a few decades of further science development to be able to fully appreciate how important this theory is and how great this man is.

This is an awesome book. Worth the $.

Paul D. MacLean, is my favorite neuroscientist. A man ahead of his time. His work is timeless, it is the seeds to the future understanding of the brain and the mind.

Paul D. MacLean's work must be read by anyone who wants to enter the medical field.

Read it, and stimulate your Neo-Cortex.

:)