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> MacLean's Triune Brain Nonsense?
Unknown
post Jun 27, 2004, 03:55 PM
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Is MacLean's Triune Brain concept utter nonsense with no basis in neuroscience? I'm inclined to think it is, and have been told as much from many neuroscientists. Yet, the triune brain concept remains popular with laymen and the general public. Why is this? Here's an excerpt from a pro-MacLean site over his Triune Brain theory, to give you an idea of what his theory is all about.

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The neurologist Paul MacLean has proposed that our skull holds not one brain, but three, each representing a distinct evolutionary stratum that has formed upon the older layer before it, like an archaeological site :He calls it the "triune brain."  MacLean, now the director of the Laboratory of Brain Evolution and Behaviour in Poolesville, Maryland, says that three brains operate like "three interconnected biological computers, [each] with its own special intelligence, its own subjectivity, its own sense of time and space and its own memory".  He refers to these three brains as the neocortex or neo-mammalian brain, the limbic or paleo-mammalian system, and the reptilian brain, the brainstem and cerebellum (see above diagram).  Each of the three brains is connected by nerves to the other two, but each seems to operate as its own brain system with distinct capacities.

This hypothesis has become a very influential paradigm, which has forced a rethink of how the brain functions. It had previously been assumed that the highest level of the brain, the neocortex, dominates the other, lower levels. MacLean has shown that this is not the case, and that the physically lower limbic system, which rules emotions, can hijack the higher mental functions when it needs to.

It is interesting that many esoteric spiritual traditions taught the same idea of three planes of consciousness and even three different brains. Gurdjieff for example referred to Man as a "three-brained being".  There was one brain for the spirit, one for the soul, and one for the body.  Similar ideas can be found in Kabbalah, in Platonism, and elsewhere, with the association spirit - head (the actual brain), soul - heart, and body in the belly.  Here we enter also upon the chakra paradigm - the idea that points along the body or the spine correspond to nodes of consciousness, related in an ascending manner, from gross to subtle.

The Reptilian Brain.  The archipallium or primitive (reptilian) brain, or "Basal Brian", called by MacLean the "R-complex", includes the brain stem and the cerebellum, is the oldest brain.  It consists of the structures of the brain stem - medulla, pons, cerebellum, mesencephalon, the oldest basal nuclei - the globus pallidus and the olfactory bulbs.  In animals such as reptiles, the brain stem and cerebellum dominate.  For this reason it is commonly referred to as the "reptilian brain".  It has the same type of archaic behavioural  programs as snakes and lizards.  It is rigid, obsessive, compulsive, ritualistic and paranoid, it is "filled with ancestral memories".  It keeps repeating the same behaviours over and over again, never learning from past mistakes (corresponding to what Sri Aurobindo calls the mechanical Mind).  This brain controls muscles, balance and autonomic functions, such as breathing and heartbeat.  This part of the brain is active, even in deep sleep.

The Limbic System (Paleomammalian brain).  In 1952 MacLean first coined the name "limbic system" for the middle part of the brain.  It can also be termed the paleopallium or intermediate (old mammalian) brain.  It corresponds to the brain of the most mammals, and especially the earlier ones.  The old mammalian brain residing in the limbic system is concerned with emotions and instincts, feeding, fighting, fleeing, and sexual behaviour.  As MacLean observes, everything in this emotional system is either "agreeable or disagreeable".  Survival depends on avoidance of pain and repetition of pleasure.

When this part of the brain is stimulated with a mild electrical current various emotions (fear, joy, rage, pleasure and pain etc) are produced.  No emotion has been found to reside in one place for very long.  But the Limbic system as a whole appears to be the primary seat of emotion, attention, and affective (emotion-charged) memories.  Physiologically, it includes the the hypothalamus, hippocampus, and amygdala.  It helps determine valence (e.g., whether you feel positive or negative toward something, in Buddhism referred to as vedena - "feeling") and salience (e.g., what gets your attention); unpredictability, and creative behaviour. It has vast interconnections with the neocortex, so that brain functions are not either purely limbic or purely cortical but a mixture of both.

MacLean claims to have found in the Limbic system a physical basis for the dogmatic and paranoid tendency,  the biological basis for the tendency of thinking to be subordinate feeling, to rationalize desires.  He sees a great danger in all this limbic system power.  As he understands it, this lowly mammalian brain of the limbic system tends to be the seat of our value judgements, instead of the more advanced neocortex.  It decides whether our higher brain has a "good" idea or not, whether it feels true and right.

The Neocortex, cerebrum, the cortex , or an alternative term, neopallium, also known as the superior or rational (neomammalian) brain, comprises almost the whole of the hemispheres (made up of a more recent type of cortex, called neocortex) and some subcortical neuronal groups. It corresponds to the brain of the primate mammals and, consequently, the human species.  The higher cognitive functions which distinguish Man from the animals are in the cortex.  MacLean refers to the cortex as "the mother of invention and father of abstract thought".  In Man the neocortex takes up two thirds of the total brain mass.  Although all animals also have a neocortex, it is relatively small, with few or no folds (indicating surface area and complexity and development).  A mouse without a cortex can act in fairly normal way (at least to superficial appearance), whereas a human without a cortex is a vegetable.

The cortex is divided into left and right hemispheres, the famous left and right brain.  The left half of the cortex controls the right side of the body and the right side of the brain the left side of the body.  Also, the right brain is more spatial, abstract, musical and artistic, while the left brain more linear, rational, and verbal.

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rhymer
post Jun 27, 2004, 04:03 PM
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I hadn't realised Mclean was the source of this theory, which seems sensible to me from my own experiences.
I don't really bother whether there are three brains as separate entities, considering them myself as three 'layers' of development. Each has specialised functions for survival which may or may not be superceded by higher levels.
It seems to fit in with evolutionary ideas, and the way different groups of functions disappear as a brain nears death [ie., an ascendency of functions which decays in order of complexity].

What alternative theories exist?
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Unknown
post Jun 27, 2004, 04:18 PM
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QUOTE (rhymer @ Jun 27, 04:03 PM)
What alternative theories exist?

MacLean makes appeals to evolutionary theory too, but the problem is that a real reptilian brain is nothing like the reptilian brain (or R-complex) of MacLean. I agree that MacLeans division of the brain into 3 main subsystems has some functional and anatomical utility, but to call one of them the reptilian brain implies we have a reptile's brain as a subsystem in our brain, and that isn't anywhere close to the truth.

MacLean's theory is inclusive of the entire brain, and I am not aware of such neatly packaged alternatives, other than to explain the brain, not in terms of three subsystems, but rather in terms of many more subsystems that interact and which, in some cases, do not possess clearly defined boundaries.

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Paul King
post Oct 09, 2005, 10:32 PM
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QUOTE (Unknown @ Jun 27, 03:55 PM)
Is MacLean's Triune Brain concept utter nonsense with no basis in neuroscience?  I'm inclined to think it is, and have been told as much from many neuroscientists.  Yet, the triune brain concept remains popular with laymen and the general public.  Why is this?

Actually, I believe there is a lot to this idea.

To say that we have "three separate brains" is a little bit silly. But I also think this is a misunderstanding of the concept.

What does seem to be the case, and there is a lot of experimental evidence for this, is that the brain has three basic layers. Each layer extends and physically wraps the more primitive layer below it. And each layer, in extending the older layers, transforms the overall character and behavior of the system as a whole.

The problem with seeing these as "three separate brains" is that it implies that each one operates independently of the others and could exist without the others. It is more accurate to say that each more recent layer augments the capacity of the layer below it. And each newer layer has some ability to override the layer below it.

The brain stem ("reptilian brain") keeps the body alive. It decides when we wake up and when we go to sleep and keeps us breathing.

The limbic system ("paleomamalian brain") directs the overall behavior of our body when we are awake. It makes us obsess over food when our blood sugar is low. And it makes us do "irrational things" in order to have sex, protect children, and defend ourselves.

The neocortex ("neomamalian brain") has all of our memories. This is the organ within our brain that notices complex patterns, experiences reality, and remembers the past. It's job is "to put 2 and 2 together" to build an operational model of the world geared toward survival. This part of the brain is functioning as an active, adaptive, pattern matching memory. It is consulted for behavior, but it doesn't drive it.

The way to think of it, then, is that the brain stem turns the brain off at night so it can recharge, and it keeps the body from being destroyed as best it can. The limbic system runs the show, but it does not know what show it is running. The neocortex has all the detail regarding what is best to do at each micro-moment. But it is only able to give advice. The limbic system must take the advice, even though it does not understand it.
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Rick
post Oct 10, 2005, 10:40 AM
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Perhaps if we think we understand the brain we have over-simplified it. We should also note that the older brain portions have kept evolving right along with the growth of the neocortex. Today's reptilian brain may be much more capable than the brains of reptiles that lived 300 million years ago.
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Hey Hey
post Oct 10, 2005, 02:55 PM
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QUOTE (Rick @ Oct 10, 07:40 PM)
Today's reptilian brain may be much more capable than the brains of reptiles that lived 300 million years ago.

Is there any palaeontological record to support this, specifically for the brain (say in the topology of the skull's interior)?
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Rick
post Oct 11, 2005, 09:47 AM
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The crocodilians have had similar body form for 300 million years. It would be interesting to see brain size per body weight graphed as a function of time.
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Hey Hey
post Oct 13, 2005, 06:57 PM
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QUOTE (Rick @ Oct 11, 06:47 PM)
It would be interesting to see brain size per body weight graphed as a function of time.

Agreed.

This is a job for Shawn!?
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rhymer
post Oct 14, 2005, 12:00 PM
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There is a lot of possibly relevant (at least related) info here

http://www.bbsonline.org/Preprints/OldArch...bbs.finlay.html
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Unknown
post Oct 14, 2005, 03:24 PM
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QUOTE (rhymer @ Oct 14, 12:00 PM)
There is a lot of possibly relevant (at least related) info here

http://www.bbsonline.org/Preprints/OldArch...bbs.finlay.html

good link!
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Hey Hey
post Oct 15, 2005, 12:39 PM
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QUOTE (rhymer @ Oct 14, 09:00 PM)
There is a lot of possibly relevant (at least related) info here

http://www.bbsonline.org/Preprints/OldArch...bbs.finlay.html

thanks rhymer. certainly a good start.
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Paul King
post Oct 17, 2005, 12:59 AM
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QUOTE (Rick @ Oct 10, 10:40 AM)
We should also note that the older brain portions have kept evolving right along with the growth of the neocortex. Today's reptilian brain may be much more capable than the brains of reptiles that lived 300 million years ago.

Certainly!

Although while the older parts have been evolving, they have probably been evolving more slowly than the newer parts. (It is a pattern in evolution that older things evolve more slowly because they are the foundation on which the newer things depend. Changing them can be catastrophic.)

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Enki
post Oct 29, 2005, 03:30 PM
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Oho!
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Unknown
post Oct 29, 2005, 04:03 PM
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Hi Enki,

are these the three layers?

Obsolete.
Hopeful.
Over-the-top.

Hence Oho?
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Enki
post Oct 30, 2005, 01:51 AM
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Hi Unknown,

Oho means oho my dear. wink.gif

Bests,
Enki
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rhymer
post Oct 30, 2005, 04:15 PM
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Thanks Enki, but I must admit, I thought that was what Father Christmas said?
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Enki
post Nov 06, 2005, 12:40 PM
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QUOTE (rhymer @ Oct 30, 04:15 PM)
Thanks Enki, but I must admit, I thought that was what Father Christmas said?

You are welcomed!

Keep in secret that you have a secret to keep. That is my motto from the beginning of the times. You know that is an excellent motto. wink.gif

It is good that Father Christmas said so, but now I have said that too. So will you be so kind to update your list quotations.

Yours,
Enki
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Unknown
post Nov 24, 2005, 12:08 PM
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QUOTE (Paul King @ Oct 09, 10:32 PM)
QUOTE (Unknown @ Jun 27, 03:55 PM)
Is MacLean's Triune Brain concept utter nonsense with no basis in neuroscience?  I'm inclined to think it is, and have been told as much from many neuroscientists.  Yet, the triune brain concept remains popular with laymen and the general public.  Why is this?

Actually, I believe there is a lot to this idea.

To say that we have "three separate brains" is a little bit silly. But I also think this is a misunderstanding of the concept.

What does seem to be the case, and there is a lot of experimental evidence for this, is that the brain has three basic layers. Each layer extends and physically wraps the more primitive layer below it. And each layer, in extending the older layers, transforms the overall character and behavior of the system as a whole.

The problem with seeing these as "three separate brains" is that it implies that each one operates independently of the others and could exist without the others. It is more accurate to say that each more recent layer augments the capacity of the layer below it. And each newer layer has some ability to override the layer below it.

The brain stem ("reptilian brain") keeps the body alive. It decides when we wake up and when we go to sleep and keeps us breathing.

The limbic system ("paleomamalian brain") directs the overall behavior of our body when we are awake. It makes us obsess over food when our blood sugar is low. And it makes us do "irrational things" in order to have sex, protect children, and defend ourselves.

The neocortex ("neomamalian brain") has all of our memories. This is the organ within our brain that notices complex patterns, experiences reality, and remembers the past. It's job is "to put 2 and 2 together" to build an operational model of the world geared toward survival. This part of the brain is functioning as an active, adaptive, pattern matching memory. It is consulted for behavior, but it doesn't drive it.

The way to think of it, then, is that the brain stem turns the brain off at night so it can recharge, and it keeps the body from being destroyed as best it can. The limbic system runs the show, but it does not know what show it is running. The neocortex has all the detail regarding what is best to do at each micro-moment. But it is only able to give advice. The limbic system must take the advice, even though it does not understand it.

interesting, but the devil is in the details.
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avisolo
post Jan 14, 2006, 10:54 PM
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Read what Maclean himself said about it here:
http://www.d.umn.edu/~rlloyd/EducatorsInstitute/Mac2.htm
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Unknown
post Jan 15, 2006, 01:11 AM
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QUOTE (avisolo @ Jan 14, 10:54 PM)
Read what Maclean himself said about it here:
http://www.d.umn.edu/~rlloyd/EducatorsInstitute/Mac2.htm

It's a good link and makes for an interesting read but I still think Maclean's triune brain concept is childishly naive and explains nothing. Anyone sufficiently appreciative of the brain 's organization and complexity will tell you the same thing.
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Paul King
post Mar 15, 2006, 02:03 PM
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QUOTE(Unknown @ Jan 15, 01:11 AM) *

QUOTE(avisolo @ Jan 14, 10:54 PM)
Read what Maclean himself said about it here:
http://www.d.umn.edu/~rlloyd/EducatorsInstitute/Mac2.htm

It's a good link and makes for an interesting read but I still think Maclean's triune brain concept is childishly naive and explains nothing. Anyone sufficiently appreciative of the brain 's organization and complexity will tell you the same thing.

The value of the triune brain concept is as a point of view, not as an explanation of mechanism. It is a systemic way of thinking about the cause of behavior that is an improvement over Freud but still a long way from what is "really" going on.

The strength of the idea (the intuition, really), is that most instinctual behaviors (what he calls ancestral memories selected by evolution) are encoded in the circuits and pathways of the limbic system and below. Conversely, most cognitive functioning, acquired memories and skills are encoded in the cerebral cortex.

Current theories still support this basic separation, however the models have come a long way since MacLean's time. The neocortex, for example, is not at all separate and independent from the older parts of the brain. MacLean did not say that it was, but he did seem to talk about it that way. What MacLean really said was that the limbic system is a fairly self-contained, tightly interconnected system, and current theories would not contradict that.

Today's explanations of brain mechanism focus much more on statistical learning models and pattern classification. The current models around emotion tend to map the phenomena people associate with emotions onto reinforcement learning and behavior strategy selection paradigms. The trend these days seems to be not so much in understanding instinctual wiring, but in understanding learned behaviors. Learned behaviors are often the interaction of certain neural pathways and circuits (which could be called instinctual) with structured adaptive processes that lead to the formation of optimal behavior.

Emotions are being understood these days in terms of neurotransmitter systems and their relationship to behavior strategy optimization processes, for example, the study of "neuroeconomics" and neural mechanisms of decision making, risk assessment, and exploratory learning.

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lucid_dream
post Sep 19, 2006, 07:38 PM
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Paul MacLean should have recanted his utterly ridiculous Triune Brain Theory decades ago.

It's amazing that you still find blatantly false theories of the brain floating around! MacLean's theory is right alongside Aristotle's notion of the brain as a cooling system.
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TaylorS
post Jan 31, 2008, 06:54 PM
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IMO the Triune Brain hypothesis is at most, a profound oversimplification. Our brain stem, cerebellum, and mid-brain are not unchanged relics, they have evolved right along with the cerebrum, it's just not as obvious because evolution tends to be conservative and economical, you don't need to create new structures if you can just "reprogram" structures already there for new purposes. The cerebellum, especially, does not get the respect it deserves; it's not only important in coordinating movement, but is also plays a role in coordinating our thought patterns. Certain parts of the thalamus are vital in maintaining a state of conscious awareness, damage to those regions will turn you into a vegetable.
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Robert B. Mounts
post May 16, 2011, 11:29 AM
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Let's examine the question from a different point of view.

Humans certainly respond to stimuli in different set patterns 'as though' three different operating systems were at work.

'R-complex' may not refer to a specific structure that emulates a rattler. But the reactive behavior patterns of 'see-strike' make a great deal of trouble for human beings, and many, perhaps most, people experience them (to their own amazement and dismay.)

Simple observation leads us to the conclusion that people are/act like mammals a good part of the time -- nurturing young, organizing as groups or packs, often around an alpha male, even coordinating tasks and attacks as a unified society. (Do most mammals, then, 'communicate'?)

And cerebral behavior -- "before you do, think it through" -- is the pride of our species, though a lot more often discussed and prescribed than undertaken.

These response patterns seem to occur at different times, under different conditions, in the same individual, so that others with with whom the respondent interacts later would think they had met an entirely different person.

So perhaps the 'triune brain' theory, as Carl Sagan presented it, is only a catchy, back-formed metaphor that essentially represents a widely recognized psychological pattern?
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dtubin
post Mar 16, 2012, 06:14 AM
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QUOTE(Robert B. Mounts @ May 16, 2011, 08:29 PM) *

Let's examine the question from a different point of view.



I couldn't agree more. If we leave alone physiological side which everyone seemed to struggle with.. It seems perfectly consistent with behavioral human model.

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Flex
post Mar 16, 2012, 06:57 AM
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IMO the only thing of importance to take away from all of that is that, "it had previously been assumed that the highest level of the brain, the neocortex, dominates the other, lower levels. MacLean has shown that this is not the case, and that the physically lower limbic system, which rules emotions, can hijack the higher mental functions when it needs to."

If you want answers, don't look to science. At best you will get a theory. Things cannot be proven, only disproven. I believe one ought to take their daily dose of scientific papers with a grain of salt, in the understanding that 50 years down the road the entire picture will be different. We can model molecules with ball and stick models that do not represent reality in anyway, yet it is a very useful tool, just as this model has been useful. Doesn't mean it is correct smile.gif
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Jakare
post Mar 16, 2012, 11:47 AM
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If we are going to split the brain appart we should say there are 5 two 7 different brains depending upon if we want to think of the limbic system as divided in hemispheres or not like the neocortex is and counting the cerebellum aswell. The cerebellum itself is a really complex structure and is divided in two aswell.

But the more relevant division between brain structures is right and left hemispheres IMO hands down. The studies about corpus callosotomy are deeply amazing about how differently those two little fellas inside us can have a very different point of view.
http://www.intropsych.com/ch02_human_nervo..._operation.html
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