It’s Not All in The Mind! Some Physical Differences Between Introverts And Extroverts


You prefer to curl up and read a book by yourself over going to a flashy social event. You like the company of one close friend rather than a group of many rowdy people. Once more you prefer to stay on the safe side than take risks. Does this sound familiar? If so, then you are probably an introvert and more recently labelled A HIGHLY SENSITIVE PERSON. You may already know this but what you may not be aware of is that there are physical differences in how you use your brain that make you prefer quiet activities over those that are highly energised. Your senses create hyper-arousal in situations that to more extroverted types are fun and energising.

Carl Jung’s studies

It was Carl Jung who in the 1920s coined the terms introvert and extrovert. He did so to describe contrasting personality types and to explain why different people were energised in distinct ways. He hypothesised that extroverts gained their energy from their social interactions and eternal environments and tended to feel uncomfortable and anxious when they found themselves alone.

Introverts, on the other hand, Jung explained, are able to replenish their energy levels when they are in quiet environments. Unlike extroverts they find socialising and busy environments overstimulating and too demanding.

Introversion and extroversion are not black and white. No one is completely one way or another – we all must function at times on either side of the continuum.

Introversion and extroversion are at the opposite ends of the same spectrum. Everybody moves up and down the spectrum depending on external and internal factors, however, a person tends to prefer one personality type over the other.

In recent times the term ambivert has been introduced to describe the middle personality type. I have written about it previously and to be honest I am not so sure it actually exists but it does describe an ideal that is balanced and gives the best of both worlds. The golden mean between two opposites. The grey between the black and white. The perfect third created by the fusion of the two. Perfection. This third between opposites normally has to be attained and rarely if ever can be maintained for any length of time. This is true for all opposites. We all know what would be ideal but very few people live their lives in the ideal place. Maybe nobody.

The Dopamine difference

A major difference between the brains of introverts and extroverts is the way they react to the neurotransmitter dopamine.

Dopamine is a chemical that is released in the brain. It gives a person their motivation to achieve external goals and receive external rewards. For example, dopamine may motivate an individual to earn more money, increase their circle of friends, attract a good looking partner or advance to a higher role at work. When dopamine is released all of us become more alert to our surroundings, more talkative and more motivated to undertake activities that may be perceived as risky.

Introverts and extroverts have equal amounts of dopamine in their brains, however, the difference between these two categories of people is the activity of the dopamine reward network. The dopamine reward network is more active and dynamic in the brains of extroverts. When an extrovert anticipates a social event, for example, they feel good and energised, whereas the introvert will feel overstimulated.

Acetylcholine and Introverts

Acetylcholine is related to pleasure, just like dopamine, however acetylcholine makes a person feel good when they turn inward. It gives a person the skill to reflect and focus solely on an individual task for an extended period of time. As it is simpler to turn inwards when there is limited external stimulation, introverts opt for a calm environment.

Introverts prefer one side of the nervous system over the other

The nervous system is divided into two distinct parts: there is the sympathetic side which is related to the “fight, fright, or flight” response; and the parasympathetic side. The parasympathetic side allows us to rest and digest.

When the sympathetic side is stimulated the body prepares for action; adrenaline is released, glucose energises the muscles and the amount of oxygen in the body increases. The thinking mechanisms in the brain are put on hold. Dopamine increases alertness in the rear of the brain.

When the parasympathetic side of the brain is in gear; muscles relax, energy is stored and food is metabolised. Blood flow and alertness in the front of the brain increase as acetylcholine is released.

Although extroverts and introverts use both sides of the nervous system, various times introverts tend to prefer to use the parasympathetic side. This allows introverts to be calm and to act in a slow and measured way.

Why introverts tend to overthink

When information from the external world is received by an extroverts brain it travels via a short pathway that goes through the areas of the brain where touch, taste, sound and sight are processed.

When introverts receive stimulus from the outside world the pathway that the information travels through is a lot longer. The information goes through many areas of the brain including:

  • The right front insular,
  • Broca’s area,
  • The right and left frontal lobes and, the left hippocampus.

The right front insular is an area involved with empathy, emotional thought and self-reflection.

The Broca’s area activates self-talk and plans speech.

The right and left frontal lobes, plan and select ideas and actions.

The left hippocampus decides what things are personal and places them in long-term memories.

The long journey that the information takes when an introvert receives stimulus from the external world is the reason that introverts take longer to speak, react and make decisions. Or more obviously think hard about everything. Analysing deeply even the simplest situation.

Introverts have more grey matter in the front of their brains

A study published in the Journal of Neuroscience discovered that introverts have larger, thicker grey matter in their prefrontal cortex. The prefrontal cortex is the place in the brain that is linked to abstract thought and decision-making. Extroverts, on the other hand, have thinner gram matter in the same area.

What does this mean?

It means that introverts devote more of their energy and resources to abstract thought while extroverts have the propensity to live in the moment.


Things may now make more sense to you, as an introvert. You can now understand that there are physical differences in your brain that make you prefer peaceful activities and self-reflection over highly energised situations. And as an extrovert why you like to be with people and impulsively react, seemingly without a thought. At least not as much thought as your very stressed introverted friend or colleague who is busy analysing while you are already doing.

If you like my writing or it at least gets you thinking – please check out my books here.

Adam Senex