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Medical Triune brain as a model for explanation

  1. Jun 20, 2010 #1
    Triune Brain

    Not rigorous enough for pure neuroscience. But rigorous enough for people to grasp the brain?

    The actual reality is complex and gritty. Yet we don't explain the reality of quantum physics- we present simple, understandble analogies for people to grasp.

    My question to neuroscientists here. Can this be used as a basic explanation of our brain function? As far as I can tell the limbic system exists in many mammals yet not in reptiles. And the neocortex is grossly enlarged in humans.

    Wikipedia doesn't have any good articles on brain evolution and I'm looking for a model to elegantly explain brain evolution from primitive amniotes. The triune brain offers me this and is it terribly invalid for me to say:

    > R-complex in early tetrapods
    Fear, aggression, violence. Instinctual
    > Limbic system greatly enlarged in early mammals
    Emotion, empathy, love
    > Neocortex, massively expanded in early apes
    Logic. Foresight. And reason.


    How about birds? Early amniotes -> therapsids -> mammals. OR amniotes -> archosaurs -> birds. Yet birds have a well developed Neocortex. This structure must have been present in primitive amniotes. Were they just very small and later expanded?

  2. jcsd
  3. Jun 21, 2010 #2
    I'm not a neuroscientist and am just answering as someone who does a lot of reading about the brain.

    You might want to read The Man Who Tasted Shapes, by Richard Cytowic. He goes on and on about what he perceives as misconceptions about the triune brain. His main contention is that the notion the cortex superceded the limbic system is false, and that, in fact, the limbic system is, and always has been, fundamentally 'in charge'. The neocortex simply serves as a tool to make it better informed. We have not abandoned emotion at all to become creatures of logic, forsight, reason. We remain essentially emotional, but our emotions are better informed. Cytowic is, of course, completely right about this.
  4. Jun 22, 2010 #3


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    The triune brain does still have an appealing simplicity and a small grain truth but probably ends up misleading more than it informs.

    For instance, all vertebrates have a limbic system. And the limbic system itself sounds an outdated idea these days - the idea of some kind of emotion circuit, with the neocortex being the rational part of the brain.

    The problem with this kind of approach is that it is attempting to see the brain in engineering terms as a collection of modular functions, whereas the brain is a highly integrated organ. A better lens than modularity is to see the brain in terms of a processing hierarchy, and hence in terms of various functional dichotomies.

    For example, a major dichotomy is stability~plasticity. The lower brain is highly stable - genes build brainstems and their responses are highly reflexive. The higher brain is instead highly plastic and so built by learning and creative in response.

    Or another major dichotomy is what~where, the division of the brain into its ventral object recognition path and dorsal spatial awareness path.

    Or into event~context - the division particularly in humans into a focal left brain and contextual right brain.

    Or into habit~attention - the division between sub-cortical "emitted" responses and cortically developed responses.

    Or sensory~motor - the divide between the front and back halves of the cortex.

    So you have a bunch of broad divisions of labour that cut across the brain in various directions. Very confusing perhaps - not an easy story like the triune brain. But once you get the connection between dichotomies and hierarchies, then you start to get a real sense of how brains work (and how deeply unlike a computer or machine it is).
  5. Jun 22, 2010 #4
    wow! great posts! especially apeiron- wonderful description there. thank you ;)
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