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5 Scientific Facts About the Introvert Brain

introvert brain science

Coined by Carl Jung in the early 20th century, the terms “introversion” and “extroversion” have gained widespread popularity thanks to the prevalence of human personality theories in online circles. 

Questionnaires such as the Myers–Briggs Type Indicator or Raymond Cattell’s 16 personality factors make use of the concepts, making them well-known among those who seek to better understand themselves and their behavior. Nowadays, most people savvy enough to enjoy personality questionnaires will identify themselves as “introverts” or “extroverts.”

Determining the exact distribution of introverts and extroverts worldwide is nothing short of impossible. However, certain studies speculate that introverts make up for anything between one-third and one half of the world’s population, leaving their numbers rather even.

And yet, despite being relatively common, introversion is still commonly misunderstood by the general public, including introverts themselves. 

But current scientific studies do not share these proclivities. Instead, multiple independent researchers have discovered a few essential elements needed to understand the biology, science, and psychology behind introversion and extroversion.

As it turns out, introversion is more complicated than just not enjoying loud parties.

1. Introversion refers to reactions to the environment. 

The first aspect to understand about introversion is its very definition. Often misunderstood as shyness, depression, rudeness, or anxiety, introverts are regularly the target of many misconceptions and stereotypes that hardly have any relation to the concept itself.

Introversion and extroversion, as conceptualized by Carl Jung, are personality types defined by the primary source of gratification for each individual. As such, extroverts tend to focus their energy and interests towards the external, outside world, while introverts prefer to orientate their lives inwards, directing their attention towards their inner world. 

As such, introverts tend to feel rewarded and gratified by introspective activities and are energized by the quintessential “alone time”. However, the preferred activities of extroverts—interacting with the external environment and prolonged socialization—drain introverts’ drive and overwhelms their senses after some time, making them seek solitude to rest and “recharge” energy. 

2. Introverts and extroverts favor different sides of their autonomic nervous system. 

As mentioned above, introverts are energized by their inner world and exhausted by prolonged interaction with the outside world. However, what may seem like a simple preference is often a biologically-wired fact. 

Amongst the many components of the nervous system, the autonomic subdivision stands out as the one responsible for the involuntary movements and actions performed by the human body, including all the internal functions.

The autonomic nervous system has two main branches—the sympathetic and parasympathetic nervous systems, both in charge of involuntary impulses but vastly different from one another. 

So far, this may seem unrelated to introversion, but there is nothing further from the truth. While all humans use both systems during certain occasions, scientific studies have determined introverts are those that tend to favor the use of the parasympathetic side unconsciously. To no surprise, this is often called the “rest-and-digest” system, stimulating the body to slow down, relax, and save energy. 

Contrastingly, the sympathetic nervous system is referred to as the “fight-or-flight” branch, for it stimulates the body to take action through the release of adrenaline. Naturally, this is the one favored by extroverts.

3. Introverts are highly sensitive to dopamine. 

Although it isn’t clear why some individuals favor one of the two branches of the autonomic nervous system, certain studies associate it with certain neurotransmitters. While each body operates with the same chemical compounds and produces them in the same manner, the brain can be more or less receptive to them. 

Specifically, Dr. Marti Olsen Laney explains in her book The Introvert Advantage that it all boils down to the brain’s sensitivity to dopamine, a hormone associated with pleasure. In simple terms, dopamine production provides instant happiness when the individual interacts with the environment in new ways. It encourages risk-prone behavior to seek the satisfaction of a reward.

While all neurotypical individuals have the same amount of dopamine in their brains, Dr. Laney affirms that introverts are highly sensitive to dopamine, while extroverts have low sensitivity. Subsequently, extroverts need to seek more outside stimulation to feel the happiness provided by the hormone, while introverts can become overstimulated rather quickly.

4. Acetylcholine is the happiness hormone for introverts. 

Dopamine can overwhelm introverts, causing a conundrum for them—after all, dopamine is the pleasure and reward hormone. How will introverts enjoy the rush of satisfaction after achieving a goal? 

The answer is acetylcholine.

Instead of rewarding the individuals with a bolt of energy, acetylcholine is a neurotransmitter that provides relaxation and calmness. As such, acetylcholine stimulates a person when they turn inwards and engage in introspective activities. 

Acetylcholine’s effects are so mellow and gentle that extroverts cannot perceive them with their nervous system’s low sensibility, which explains why they often cannot find prolonged enjoyment or pleasure from quiet alone time. By contrast, introverts’ highly sensitive nervous system finds itself plenty satisfied with acetylcholine’s gentle touch. 

5. Introverts are biologically wired to overthink. 

While acetylcholine seems to reward introverts for being mellow fellows, its effects are not always beneficial. In fact, their predisposition to this neurotransmitter may also be the explanation behind most introverts’ propensity to overthinking.

Neurotransmitters, as their name indicates, transmit the messages perceived from cell to cell, following a specific “pathway” that determines which parts of the brain receive the message. So, when someone listens to another person’s voice or reads a book, the neurotransmitter sends the information to the brain through a given road.

According to Dr. Laney, the pathway followed by acetylcholine is longer and far more complicated than that of dopamine. Dopamine, it turns out, follows a shorter road that enables the brain to perform “quick” responses, explaining their dynamic behavior.

On the other hand, acetylcholine has a longer path that activates many more areas of the brain, making introverts process information more slowly yet more carefully. Naturally, this accounts for introverts’ propensity to overthinking, hesitate before making decisions, and engage in careful analysis of the information received.

Although these biochemical characteristics explain certain predispositions, they do not account for an individual’s full personality. Introversion does not equal intelligence, shyness, or any other stereotype that may abound online.

It does, however, explains some people’s preference towards the simpler pleasures in life.

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