THINKER'S ALMANAC - May 1

How is the human brain like a city that has existed since ancient times?

Subject:  Brain Anatomy - The Triune Brain

Event: Birthday of neuroscientist Paul Donald MacLean, 1913 

With modern parts atop old ones, the brain is like an iPod built around an eight-track cassette player. -Sharon Begley

You possess the most extraordinary thing we know of in the universe.  It’s smaller than a breadbox, weighs about three pounds, and is located between your ears. It’s the organ in our body that gives us consciousness, and it is so sophisticated that it can study itself.

One man who contributed much to our understanding of the human brain was born on this day in 1913.  He was neuroscientist and psychiatrist Paul D. MacLean, who we can credit with understanding how our brain evolved and how we should consider the fact that our brain is actually three brains in one.

MacLean’s theory of the triune brain began with his research into how the brain's physiology relates to human emotions and behaviors.  He coined the term “the limbic system” in 1952 to describe the mammalian brain, which controls fight-or-flight responses, reproductive behavior, and emotions related to sensations of pleasure and pain.  The limbic system includes the hippocampus, amygdala, and thalamus, brain parts that are essential for memory, emotions, and the senses, respectively.

In addition to the limbic system, MacLean identified the brain’s oldest part, the brain stem or “lizard brain,” which maintains the most basic functions of survival, such as breathing, heart rate, hunger, and sleeping.  The brainstem is the gateway between the brain and the body -- all the body’s sensory signals pass up through it to the brain, and all the brain’s commands for movement pass down it to the body.

The third part of the triune brain is the neocortex, which features the two hemispheres of the cerebrum (Latin for “brain). The neocortex is the seat of our higher functions, such as reasoning, decision making, and language.  It is also the largest part, making up 80 percent of the total brain (1).

MacLean’s explanation of the triune brain helps us to understand the way our brain evolved, beginning with the oldest part, the lizard brain, then to the more advanced limbic system, and finally to the consciousness-creating newest part: the “neo” cortex.  In his book The Ravenous Brain, Daniel Bor uses a description of the architectural history of Cambridge, England, as an analogy for how the brain evolved and how we see vestiges of the old at its core with the new parts surrounding it:

Our brains are rather like a city that has existed since ancient times.  In Cambridge, for instance, the historic center is squashed inside a fertile bend in the river Cam. This is the core of the city. Here there used to be a castle on a small hill, originally built by William the Conqueror in the eleventh century.  The oldest parts of the university, along with old churches and so on are still there. Over the centuries, housing, university colleges, and research departments have sprung up around this central district.  And now, around this second band of somewhat old structure, there are the outer suburbs, with modern housing along with large technology and business parks.  Though an unromantic person might be tempted to replace the oldest buildings of the city and the narrow winding roads of the core area with efficient modern streets and buildings, all these ancient places still serve some purpose today. (2)

Recall, Retrieve, Recite, Ruminate, Reflect, Reason:  What are the three parts of the triune brain, and what are the functions of each?

Challenge - Brain Anatomy Analysis:  Identify one specific part of the brain (such as the hippocampus, the amygdala, the thalamus, or the pons) and do a bit of research to identify the functions of that one part.  Explain how specifically this one part of the brain contributes to the whole brain and whole body.

ALSO ON THIS DAY:

May 1, 1672:  Today is the birthday of English writer and politician Joseph Addison who penned one of the greatest analogies ever written, explaining the importance of reading:  

Reading is to the mind what exercise is to the body.  As by the one, health is preserved, strengthened, and invigorated; by the other, virtue — which is the health of the mind — is kept alive, cherished, and confirmed. 

Sources:

1-Pearce, Jeremy. “Paul MacLean, 94, Neuroscientist Who Devised ‘Triune Brain’ Theory, Dies.”  The New York Times 10 Jan. 2008.

2-Bor, Daniel.  The Ravenous Brain:  How the New Science of Consciousness Explains Our Insatiable Search for Meaning.  New York:  Basic Books, 2012.