triune brain recapitulated

From: Scott Chase (
Date: Thu 15 Dec 2005 - 19:00:59 GMT

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    In a previous post, I was pretty harsh on the popularized notion of the triune brain, attributed to Paul MacLean also responsible for introducing the "limbic system" concept. Joseph LeDoux was critical of MacLean's views in his _The Emotional Brain_, especially focusing on the questionable comcept of a "limbic system". LeDoux's criticisms are important and perhaps in themselves effectively torpedo the idea of a triune brain as envisioned by MacLean, but in a previous post, my focus ws on the concept of a dicrete region that one could call a "reptilian brain" (R-complex). First off the term "reptile" is problematic in classification. It is what some systematicists would refer to as paraphyletic, failing to encompass descendant groups such as birds. Everything MacLean refers to a "reptilian" may better be termed amniotic, which takes all amniotes (turtles, lizards, snakes, crocodilians, birds, and mammals into account). The basal areas
    (basal ganglia, etc) might be better seen as an amniote feature, if that indeed is true. My comparative neuroanatomy is rusty on this detail.

    But there may be a problem even with the "amniote brain" concept. LeDoux lets the cat (or "fish" out of the bag) in _The Emotional Brain_ when he says (pbk page 98): "All other vertebrate creatures (birds, reptiles, amphbians, and fishes) have only the reptilian brain". In his review of MacLean [1990, Science, vol 250, p. 303-] Anton Reiner follows the same thread saying: "...the R-complex is not a reptilian invention but seems to be present in vertebrates all the way back to jawless fishes." Thus we might not even be able to talk about a "gnathostome brain". Perhaps what MacLean has popularized as the reptilian brain is merely a widespread vertebrate feature. So not only is the "reptilian" brain a misnomer, but doesn't even stay confined within the amniotes.

    In "Man's reptilian and limbic inheritance" [found in A Triune Concept of the Brain and Behavior. 1973. University of Toronto Press] MacLean speaks of the close relation of birds and reptiles, which superficially appears as a category error, though in an earlier footnote he does break "reptiles" down to its proper extant groups and mention the actual close relation of birds and crocodilians. There are various groupings within the "reptiles" besides crocs and the foggy term "reptile" could vaporize upon closer inspection.

    Anyway in this essay MacLean makes a statement that seems relevant to memetics. He says (p. 10):

    [bq] "The reptilian brain seems to be hidebound by precedent. Behaviourally, this is illustrated by the reptile's tendency to follow roundabout, but proven, pathways, or operating according to some rigid schedule. Customs of this kind appear to have some survival value and raise the question as to what extent the reptilian counterpart of man's brain may determine his obeisance to precedent in ceremonial rituals, religious convictions, legal actions, and political persuasions." [eq, MacLean's self-reference to previous work omitted]

    One wonders what determines our propensity to follow a tradition as set in stone as the "limbic system" concept (see LeDoux) or the "triune brain" concept. This, in itself, might be a good study for memetics on how popular psychological notions have spread through our culture and impacted other realms of thought. How widespread is the "triune brain" concept and how seriously is it taken?

    After the above quoted passage, MacLean makes an interesting reference to site fidelity in sea turtle females laying their eggs in some strange sense portraying this activity as obsessive-compulsive as if turtles are manifesting an ancient form of OCD when they return to the same beaches. I'm speechless. MacLean does earlier make the point that the turtle's brain is structurally close to that of protomammalian reptiles, though his favorite subject of lizards are better to study behaviorally, even though lizards are just convenient surrogates for our ancestors.

    Returning to MacLean's theme of the cultural aspects of our reptilian brain, in a later work he talks about "isopraxic behavior" (imitation, mimicry, social facilitation...). I like the term isopraxis. MacLean says [page 239, The Triune Brain in Evolution, 1990, Plenum Press, New York]: "Since destruction of parts of the R-complex in both lizards and monkeys interferes with display behavior, it might be inferred that the corresponding [MacLean dislikes "homology"] structures in each species are implicated in conspecific recognition and the expression of isopraxic behavior."

    There's a point in MacLean's above cited "Man's reptilian and limbic inheritance" where he waxes protomemetically. This book was published in 1973 but the actual lecture may have occurred in 1969. He says (page 20):
    "Indeed, it is questionable whether or not the human race could survive without limbic emotions because, whatever else they do, they assure conflict and argument which in turn insure the mixing of the gene pool of ideas!"

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