To be able to understand something, you have to know enough about it. That certainly also applies to introversion, since for many people that term evokes uncertainty. Is it about being social or is it something else? And is someone necessarily introvert or extrovert, or can you be a mix of both? This is what I found out doing research on the matter.

The eight types of Carl Jung

The inventor of the term introversion was the Swiss psychologist and psychiatrist Carl Jung, who immersed himself in the personality of man at the beginning of the twentieth century.

Since classical antiquity, people have been concerned with personality, also called temperament. Until the time of Jung, this mainly concerned the ratio of certain liquids in the body: blood, mucus, bile and black bile. The fluid most present was decisive to the personality type of that person.

However, Jung decided to take a different approach. He made a distinction between introverts and extroverts based on observations of his patients and himself, noting that each person has characteristics of both, but that the proportions differ from person to person.

In addition to introversion and extraversion, Jung discovered that there were people who preferred thinking, where others would rather feel. He also saw a difference between people who trust their intuition and people who prefer sensing. He came to a total of eight different personality types. Jung defined introversion as a subjective view of the world, or a world in which the inner world of man is the starting point. This is in contrast to extroverts, who are focused on the outside world.

The sixteen types of MBTI

More than twenty years after Jung, the American Katharine Cook Briggs and her daughter Isabel Myers Briggs built on his philosophy by adding an extra dimension: judging and perceiving. Instead of eight, they distinguished sixteen different personalities in the model that they developed, now known as the Myers Briggs Type Indicator (MBTI). In this model each person is linked to four letters, which represent two main characteristics (introvert / extrovert and judgmental / perceptive) in combination with two so-called functions: thinking / feeling and intuition / sensing. In principle, every person has all eight characteristics, but in a varying ratio. That ultimately determines what type of person you are. The introverted, intuitive, thinking judger is a very different person from the extroverted, perceiving, feeling remarker. This has implications for how that person communicates, which job suits him or her best and how he or she can best develop. This makes the MBTI a popular tool with many HR departments, who regularly use it for career development.

Scientifically approved?

Because Jung relied on observations, his ideas are not considered reliable by current science. Cook Briggs and Myers Briggs didn’t have a background in psychology and based themselves entirely on the ideas of Jung. This means that their theories and models are not reproducible and therefore not scientifically justified. Scientists therefore often consider them as "gurus" in the field of personality theory. Their ideas, however, formed the basis for later research, where both introversion and extraversion are still used as a term to describe this personality trait. Research into the brain became increasingly important for that.

Big Five

In the 1970s, the British psychiatrist Hans Eysenck did research into the brain linked to introversion and extraversion. He discovered that the brains of introverts are more sensitive and therefore absorb more stimuli from their environment. As a result, they tend to isolate themselves from time to time in order to limit the stimuli. In extroverts, the brain is a lot less sensitive, which means that they are constantly looking for incentives to get new energy. Without stimuli, their brains are in a kind of sleep mode, which they can only override by actively looking for external stimuli. Hence their preference for social occasions, where they find all the incentives they need.

Eysenck came to two dimensions to distinguish people from each other: extraversion and neuroticism, also known as emotional stability. He typed people and their personality based on these characteristics. A more limited number of dimensions than with Jung and Myers Briggs, but this time based on scientific methods.

Eysenck's work forms the basis of the current views on personality. In the early eighties of the last century, scientists decided to investigate whether it was possible to arrive at five characteristics that characterise each person to a greater or lesser extent. They went through dictionaries in search of adjectives that people use to describe others. They then asked test subjects to describe celebrities based on those words. That is how they eventually came to what is now known as the Five Factor Model, or the Big Five. This model is based on five dimensions, where people score on a scale. These five dimensions include the two dimensions defined by Eysenck, namely emotional stability (also known as neuroticism) and extraversion. In addition, the scientists added three other dimensions: openness, gentleness and orderliness. All five dimensions are present in each of us, but the extent to which varies from person to person.

Because the Big Five assumes a normal distribution, most people score somewhere in the middle. So most people are pretty average when it comes to extraversion and will behave a little more extraverted in one situation and a little more introverted in another. They are called ambiverts. This also means that people who are more introverted or more extroverted are in the minority. On average, both groups make up around 16 percent each. However, as a percentage of the world's population, that is still a considerable amount.

The Big Five currently forms the basis for many assessments that are used to measure the capacities of new employees. Canadian scientists however were not satisfied with the five dimensions of the Big Five and added another sixth dimension in 2009: modesty and integrity. This is also a scale with a normal distribution, on which most people score on average. Their Hexaco model would do more justice to the cultural diversity in the world and whether or not they prefer a more modest and honest attitude.

Within both the Big Five and Hexaco, introversion is nothing more than a low score on the scale of extraversion, which, according to the researchers, equals closedness, caution, humility, self-discipline, little energy, shyness and even depression. Please note: these terms were based on the description in dictionaries and therefore not on actual observations. So there is certainly a cultural bias in its description.

Big Five links introversion to depressive thoughts in a certain sense. For this reason, the American Psychiatric Association (APA) decided to make a proposal in 2010 to include introversion as an indicator of certain mental disorders. In the proposal, the APA described introversion as "separating oneself from other people, going from intimate relationship to the world as a whole; limited experience and expression of affection and limited capacity for enjoyment. "

The concept of introversion has also been used for years in the International Classification of Diseases of the World Health Organization, which describes other health problems in addition to mental disorders. The "diagnosis" introversion is linked to schizophrenia, a condition where people suffer from delusions and the feeling of having multiple personalities. This description was maintained until the tenth version of the ICD, in which the term suddenly disappeared. The reason for this is unclear, although it is well known that American psychologist Laurie Helgoe, among others, fought for this. To her surprise, APA's proposal was never adopted, so introversion cannot be found as an indicator of mental problems. Something that is certainly not the case according to the latest insights in the field of neuroscience.


Although much is still unclear about our brain, we do know more about the areas and even the substances in our brains that are responsible for certain traits. For example, a large amount of dopamine (the happiness hormone) is linked to both extraversion and being open to new experiences, and serotonin (which regulates anxiety) is related to whether or not we are careful and conform to the prevailing norm. Testosterone (the male hormone) is related to analytical thinking, while estrogen (the female hormone) provides our empathic ability. In other words: those who have little dopamine are more introverted and also more inclined to gloomy thoughts.

Also the so-called orbitofrontal cortex, a brain lobe in front of you brain (above your eye sockets) plays a major role. This lobe is related to your need for reward, which in turn ensures the production of dopamine. The larger this lobe, the more you need a reward (external stimuli) to make more dopamine. In the case of introverts, this lobe is smaller, which makes them need less external rewards and therefore produce less dopamine. Extraversion and introversion can therefore literally be seen from the size of this part of your brain.

When we link this fact to the behavior of introverts and extroverts, we see major differences. Where extroverts look for economic and political gain and personal pleasure, introverts are generally less inclined to be guided by this. In this context, social contact could even be seen as a form of reward that extroverts look for more than introverts do.

Although dopamine is generally associated with a pleasant feeling of happiness and enjoyment, it certainly also has a downside. It can blind us to danger and even cause us to become less social in our euphoria. Extroverts usually take more risk, which means they are more often involved in things like accidents, smoking and divorce.

Brain research is also very interesting when we link it to the banking crisis, for example. If an extrovert who likes challenge has a certain gene that regulates dopamine in the brain, there is a good chance that this person will take large risks financially. However, if that person was an introvert with a gene that regulates serotonin, then that person will actually take less financial risk than others. An interesting fact that sheds new light on the discussions about the skewed relationship between men and women on Wall Street. It underlines the importance of so-called cognitive diversity, with a good mix of diverse personalities. It would be interesting to look at this from the perspective of personality. What about the relationship between introverts and extroverts? And how does that influence the choices that are made every day? Could a better balance have stifled the crisis? Or does such an environment just not attract introverts, because they are naturally inclined to strive less for rewards and are less inclined to take risks?

It is an interesting thought experiment. It probably provides new insights into the origins of the previous financial crisis and how such a new crisis can be prevented. It could provide more diversity in a world where profit is fast and scoring prevails. Wouldn't that be the ultimate form of diversity?