Scientific Evidence for Personality Type Theory

President and Chief Career Coach

This article covers recent scientific research which begins to provide the first physical evidence that supports the theory of Personality Type as put forth by Carl Jung and Myers-Briggs.

Although I have been using Personality Type since 2004, I write this article as a skeptic, because having worked in high tech for many years I know that many business leaders tend to be skeptical and cautious when it comes to accepting and adopting new theories.

Many people in leadership positions require extra proof. I know that and I respect that. You don't become the leader of a large business by taking unnecessary risks and by believing everything you hear.

I hope to provide some of that proof here.

As a high tech executive myself, I can see how the term "Personality Type" and "Personality Test" sounds about as credible and useful as a horoscope.

But, because I am very open minded, and I am always on the look out for new tools and methods, I have seen how Personality Type can be used effectively to accomplish many things such as:

  • Finding a career that fits better
  • Solving conflicts between people
  • Improving self awareness
  • Diagnosing why some teams just don't work
  • Building better teams teams
  • Leadership development
  • Increasing your rate of innovation

So now we finally have the beginnings of physical proof for Personality Type.

The Theory

Quick History and Introduction to Personality Type Theory

In the 1920's the English version of Swiss psychiatrist Cark Jung's book "Psychological Types" became available in America.

It's heavy duty reading and not easily accessible to the lay person.

In the book Jung (July 26, 1875 - June 6, 1961) described a pattern of fundamental differences that he observed in healthy people.

He noticed some people focused more on the internal world (the world in their heads) and some focused on the outer, external world of things, people, events, activities etc. Thus was born the idea of an Introvert and Extravert.

Then Jung observed that there were four fundamental mental functions that people were using and that they used them either in the inner world or the external world.

So each of the 4 functions could be used in the outer world or the inner world.

Thus we have the 4x2 = 8 "cognitive functions." These are indeed basic and fundamental, meaning that you won't find anymore.

So when we use our brains, we are using some combination of these mental functions.

How people differ is in which functions they prefer to use, which functions are their strongest and which are their weakest.

One of the most powerful uses of personality type is to get insight into where your strengths lie and what your weaknesses might look like. This is beneficial in both leadership development and self discovery.

The 4 Perceiving Functions

  • Extraverted Sensing (Se)
  • Introverted Sensing (Si)
  • Extraverted iNtuiting (Ne)
  • Introverted iNtuiting (Ni)

The 4 Judging Functions

  • Extraverted Thinking (Te)
  • Introverted Thinking (Ti)
  • Extraverted Feeling (Fe)
  • Introverted Feeling (Fi)

The Perceiving Functions

The perceiving functions are how we become aware of and absorb information. How we observe the external world and the internal world.

One way to perceive is to use a sensing function. Sensing is absorbing information using the 5 senses: hearing, smelling, tasting, touching, seeing.

If this is confusing, think of sensing as when you hear a single musical note or when you taste a sharp cheddar cheese. It's a discrete bit of tangible information that registers in your mind. It says, hey, I just heard a note that sounds like middle C. Or hey, I just tasted a really flavorful bit of cheese. That's sensing.

The other way to perceive (take in information) is to use an iNtuiting function. INtuiting is how we become aware of conceptual, intangible information. By intangible we mean you can't physically touch it. It's not solid and it is not observable with the five senses.

For example, when you smell the wonderful fragrance of a rose on a warm sunny day, if that smell triggers a flood of related thoughts or emotions or memories that is an iNtuiting function kicking in.

Perhaps a better example of iNtuiting is when seemingly out of nowhere a new idea pops into your head. Maybe you have been trying to solve a problem for days or weeks until finally Eureka, a solution pops into your mind. That is the iNtuiting function at work.

According to Personality Type Theory, sensing and iNtuiting act like opposites. If you are good at one, you will have trouble with the other. One will be a strength for you and the other will be a weakness.

The Judging Functions

The other fundamental functions you have besides perceiving is the judging functions.

The Judging functions are used to make decisions.

One type of Judging is called "Thinking." when you use the Thinking function to make decisions you use facts, data, logic, and analysis. The thinking function is done in an objective manner where you separate the decision from how it affects you personally.

The other judging function is somewhat misleadingly called "Feeling." When you use your feeling function you base your decision on how it will affect you personally, or how it will affect the people around you.

Your decision will be based on your personal values and priorities rather than objective data.

A good example of the thinking function is when you are buying a new car. If you select a white car because it will be cooler in the hot sun that the red car, you are basing the decision on objective, measurable data and facts. If you decide you would rather have the red car because it appeals to you more, it looks more sexy and exciting, that is your feeling function helping you make a decision that is consistent with your personal values.

According to Type theory, feeling and thinking are opposites. Thus if your feeling function is the strongest then your thinking function will be weaker of the two.

Please be careful that there are stereotypical biases surrounding these two functions.

Myers and Briggs Make Jung's Theory Accessible To All

Jung's theory and writing was for the most part too complicated and inaccessible for most non psychologists. Fortunately, in 1923, Katherine Briggs picked up on his work and then with the help of her daughter Isabel Myers they developed what is now known as the Myers-Briggs Personality Type.

It all started with Katherine Briggs (January 3, 1875 - 1968) who since 1917 had been closely observing difference in people and trying to figure out a system or pattern behind it. She found Jung's book in 1923 and shared it with her daughter, Isabel Briggs Myers (October 18, 1897 - May 5, 1980.) Jung's book gave her the psychological framework with which to build her system on.

Isabel Myers was something of a genius. She actually developed a number of statistical methods for validating her data, prior to having the calculators and computers we take for granted today.

In the 1940's they created a 4 letter code system to describe which of the functions are the strongest in an individual, and whether that person prefers to focus on the internal world (Introvert) or the external world (Extravert).

In her system there are 16 possible personality types.

She developed a test / assessment what can help you figure out which of the 16 types is the one that fits you the best. This is known as the Myers-Briggs Type Indicator (MBTI).

The MBTI has been used in over 100 countries. Typically several million people take it each year. It's available in several languages.

For a history of the MBTI, click here

Here are the 4 letter Personality Type Codes, with links to descriptions:


Now for the Scientific Evidence


Introversion / Extraversion Related to Blood Flow in the Brain

For many years, there was really no physical evidence to support Jung's theory of personality types. Sure, millions of people were tested each year and then hopefully had their 4 letter type codes validated by trained psychologists, but in the end we still want to see physical, concrete proof.

According to a study by Debra L. Johnson, entitled "Cerebral Blood Flow and Personality: A Positronic Emission Tomography Study," published in the February 1999 issue of the The American Journal of Psychiatry, the flow of blood throughout the brain is different for Introverts and Extraverts (

Overall, introversion was associated with increased blood flow in the frontal lobes and in the anterior thalamus. Regions in the anterior cingulate gyrus, the temporal lobes, and the posterior thalamus were found to be correlated with extraversion. The findings of the study lend support to the notion that introversion is associated with increased activity in frontal lobe regions. Moreover, the study suggests that individual differences in introversion and extraversion are related to differences in a fronto-striato-thalamic circuit.

The way I have heard this described is that the introvert's brain is naturally in an over stimulated state and thus they desire to quiet things down so they can concentrate.

The extravert's brain normally has less stimulation going on, therefore they seek out more stimulation in the way of more people, more activities, more noise etc.

Thus an introvert would prefer a more quiet home environment perhaps with a good book while an extravert would probably prefer to turn the TV on, just for some background noise.

Brain Waves Measured via EEG match up with the 8 Functions

In 2011, Dario Nardi Ph.D., a professor, researcher and personality type expert at UCLA published his findings (Neuroscience of Personality) showing that there are differences in how each of the 16 personality types use their brains.

By attaching electrodes and an EEG monitor to the heads of students, and then having them answer questions or perform certain tasks, he was able to see unique patterns as different parts of their brains lit up on the monitor.

This is perhaps the first physical proof of the 16 types and how each type uses the 8 functions differently.

Today the way you determine your 4 letter personality type is to take a test, then read descriptions of the 16 types to make sure you have the one that fits the best.

Personality assessments are not always accurate and it is very easy to through off the results.

But in the future you may be able to place a set of electrodes on your head, and have your laptop tell you what your 4 letter type is.

Brain Chemistry and Personality Type

There has been other work done in linking a person's personality type to brain chemistry.

More specifically, researchers are attempting to find links between the 16 types, and concentrations of the neurotransmitters Dopamine, Serotonin, GABA, Acetylcholine, Norephinephrine. Researchers are also looking for links to the hormones: Estrogen, Testosterone, and Oxytocin.

People are doing this research for four main reasons:

1) Looking for a connection between brain chemistry and Personality Type

2) Understanding the possibility of modifying ones Personality Type through chemistry

3) Improving medical treatment based on brain chemistry

4) Capitalizing on matchmaking and internet dating via Personality Type

Dr. Eric Braverman, a medical doctor who has done brain research and runs a medical clinic, describes in his 2005 book,The Edge Effect, a connection between 4 parts of the brain, the 4 temperaments (a grouping of the 16 Types), and the proper balance between Dopamine, Serotonin, GABA, and Acetylcholine.

In his book he offers a test to help you figure out what your temperament is, which of the neurotransmitter dominates and those where you might be out of balance. I took the test and it correctly identified my temperament.

For measuring the amount of neurotransmitters present, Dr. Braverman uses a method called BEAM™.This stands for Brain Electrical Activity Map. Although he does not explain BEAM in detail I assume it is an EEG like system where they attach electrodes to one's head. These electrodes measure brain waves and voltages.

Dr. Braverman then associates these measurements with levels of neurotransmitters.

Personally I find this method a bit indirect. However, I am not a brain scientist nor a medical doctor. Perhaps it is not practical to measure the actual concentration of neurotransmitters.

But I would like to actual measurements of these neurotransmitters versus Personality Type, and for different activities that would force the use of each of the 8 functions.


Another researcher in this field is Dr. Helen Fisher.

Dr. Fisher claims to have found links between the 4 temperaments and concentrations of neuro chemicals. However, when I read the papers I was not able to find that she used any direct method to measure the concentrations. Like Dr Braverman she used electrodes and inferred the concentration of neurotransmitters.

Dr. Fisher has been on Oprah and she consults for the dating / matchmaking web site

There is some interesting work on the hormone Oxytocin (not Oxycontin, the highly addictive pain killer). Researchers are showing a link between concentrations of Oxytocin and trust. They are starting to show that the personality types that tend to relate better with people and build stronger relationships, may have higher levels of Oxytocin.

You can already buy spray-on Oxytocin that is supposed to affect people around you by having them trust you more. Again, I'm not sure the scientific proof is all there.


Personally, after reviewing some of this evidence I think it is too early to say there is a strong connection between these brain chemicals and a person's personality type. But, it is not out of the realm of possibility. I would like to see more direct measurements of neurotransmitters. A few more years will tell for sure.


Myers-Briggs Type Indicator, Myers-Briggs, MBTI, Step I, Step II, and the MBTI logo are trademarks or registered trademarks of the MBTI Trust, Inc.,
Strong Interest Inventory, is a registered trademarks of CPP, Inc.
The CPP logo and Strong logos are registered trademarks of CPP, Inc.
CiT is a registered trademark of Inc.
There is no affiliation between the CiT and CPP. CiT is a product that is wholly owned by Inc.


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