The Fourth Brain is the PFC.

Why the fourth brain?

For instructional purposes, the human brain is often called the triune brain because it has three layers that evolved over many thousands of generations.

  1. The reptile brain runs the automatic body systems.

  2. The mammal brain is the emotional brain.

  3. The human brain is the thinking brain.

(The ‘triune model’ is not literal but is metaphorically useful)

Reptile Brain

Your inner-most, smallest and most ancient reptilian brain may well be your most treasured possession. It controls everything you value most, your life systems. It runs your body temperature, blood sugar levels, heart rate and blood pressure, your respiration, releasing hormones for all the daily house-keeping and maintaining homeostasis or balance. Your reptile brain regulates deep evolutionary maintenance and self-healing. It’s hard-earned digital wisdom has been curated over the course of a million successful generations. It’s IP value in dollarized terms is simply priceless.

Mammal Brain

Your life systems reptilian brain is in constant conversation 24/7/365 with your emotional mammalian brain. Your wide repertoire of emotions ranging from the big one – fear – and the others like shame and anger to sexual longing to surprise, joy, sadness, trust and disgust. These are all triggered and/or switched in the mammalian brain also known as the limbic system. These mood changes and emotional switches are in sync with high speed parallel processing in the reptilian brain. The reptilian brain can stimulate the mammalian brain … and, of course, vice versa.

Human Brain

Enter your BIG human brain! This newest brain, the neocortex, is also in conversation 24/7/365 with both the older brains. As you would expect, their conversations can stimulate responses in the human cortical brain … and, again, vice versa. All three evolutionary brains are in constant digital engagement up and down the neuronal layers of the triune brain (reminder that this is not literally accurate but is practically so, metaphorically).

But wait! There’s more …

The Fourth Brain is the PFC.

The PFC is the “better brain for better thinking” and better thinking is all about reappraisal.

Reappraisal is about doing the harder thing when it’s the better thing to do. It’s called willpower. It’s also called wisdom.

Wisdom and willpower are the specialised work of the PFC (pre-frontal cortex).

To develop the PFC requires more than genes. To assemble the PFC brain requires real life experience–lots of successes and lots of failures–and therefore it is the last part of the human brain to develop.

Problem: In the adolescent brain the PFC is not yet developed. The PFC doesn’t fully come online until the midtwenties.

Parents, teachers and adults already know that because they themselves have been adolescents and once experienced, in their own lives, the consequences of PFC deficit.

For example, adolescents have real difficulty detecting irony and have to work much harder in their PFC when an adult can take one look at a face and that’s enough. And, it can help explain why adolescents (with yet-to-be-developed willlpower) have three times the pathological gambling than adults have. Or, why adolescents are more likely to risk driving faster or while under an influence of peers, drugs or alcohol.

The problem is that adolescents take more risks than adults even though, without their fourth brain, they are much less adept at risk assessment. This is not cool. Fourth brain deficit can have really bad consequences.


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