What science really says about introverts and extroverts — and about the myths in between

At a party, two people stand at the edge of the room. One of them is talking brightly to everyone who passes, drifting from cluster to cluster, and seems to charge up as the evening grows louder. The other hangs back a little, watching, happier to talk for a long while with one person than briefly with ten — and after a couple of hours feels a deep, quiet pull towards home, and being alone.

Most people would say the first is an extrovert and the second an introvert. And that is roughly right. But what do those words actually mean? And — more importantly — what does science really say about the difference between these two kinds of people?

I should be honest with you: I am a pronounced introvert myself. An observer. Someone who would rather watch and listen than fill a room with words. And that is precisely why I wanted to know whether the stories that circulate about introverts and extroverts are actually true. Because a great deal is said about them that sounds lovely but simply isn’t so.

Let’s look at what we really know.

Where the words come from

The terms “introvert” and “extrovert” were made famous in the early twentieth century by the Swiss psychiatrist Carl Jung, in his work Psychological Types (1921). Jung saw it as a difference in where people draw their energy from: the extrovert turns outward, towards the world and other people; the introvert turns inward, towards their own thoughts and their inner world.

It’s worth clearing up one misunderstanding straight away: introverted does not mean “shy”, and extroverted does not mean “self-assured”. You can be a confident introvert who gives a perfectly good presentation and is then utterly worn out. And you can be a shy extrovert who needs people but is frightened of rejection. Shyness is about fear. Introversion is about energy. Those are two very different things.

The real difference: a volume dial in your head

In the 1950s and ’60s, the British psychologist Hans Eysenck carried out work that still underpins how we understand this today (later refined by others, such as Jeffrey Gray, but the core still stands). His idea, in plain language: imagine there is a kind of volume dial in your head for stimulation — sounds, bustle, conversation, impressions. In each of us, that dial is set a little differently.

In the introvert, the volume dial naturally sits rather high already. The brain is fairly stimulated even when not much is happening. That’s why an introvert becomes overstimulated more quickly by a busy party, loud music, or a long day full of people. It isn’t too little — it very soon becomes too much. The introvert seeks out quiet to bring the stimulation back down to a comfortable level.

In the extrovert, the volume dial naturally sits low. The brain needs more stimulation to reach a pleasant, alert level. That’s why an extrovert actively seeks out bustle, company, new experiences — to turn the stimulation up to a comfortable level. Silence and solitude can quickly feel, to the extrovert, like boredom or emptiness.

This explains almost everything we see from the outside. The introvert who is exhausted after a party isn’t antisocial — the dial was simply turned up too high for too long. The extrovert who can’t sit still isn’t shallow — the dial is crying out for more input.

The part of the brain that regulates this stimulation does, by the way, have a name: the reticular activating system. You needn’t remember that name. Remember the volume dial — that’s exactly what it does.

A charming little proof: the lemon-juice experiment

There’s a charming little classic experiment that supports this idea. Researchers dripped lemon juice onto the tongues of participants and measured how much saliva they produced.

The result: introverts produced more saliva than extroverts in response to exactly the same amount of lemon juice. Why? Because their nervous system reacts more sensitively to stimulation — even to a simple taste. The dial sits higher, even for lemon. A small, rather delightful sign that the difference isn’t imagined, but really does sit in the body.

The role of dopamine

There is a second difference, and it has to do with dopamine — a substance in the brain bound up with reward and motivation. It gives that pleasant “yes, more of this” feeling when something good happens.

Research shows that the reward system of extroverts responds more strongly to dopamine. An exciting social encounter, a new experience, a gamble that pays off — the extrovert’s brain hands out a hearty reward for these things. No wonder extroverts go looking for them; their brain rewards them richly.

In introverts, that same system reacts more calmly. They draw their satisfaction less from external excitement and more from quieter sources. There is a popular theory that says another substance, acetylcholine, plays a larger role in introverts — fitting with inward-turned attention, calm reflection and focus. But let’s be fair: that last point is mostly an attractive hypothesis from popular books, and not firmly proven by science. What we can say with some confidence is that an introvert can have a deeply contented afternoon with a book, while an extrovert grows restless after an hour.

Neither is better. They are simply two different ways in which a brain draws satisfaction from the world.

The big question: are introverts cleverer?

Here I have to be honest, even though I am an introvert myself and would rather like to say “yes”.

The answer is no. Science is clear on this: introverts are not more intelligent than extroverts, and extroverts are no cleverer than introverts. Intelligence is more or less evenly spread across both groups. Anyone who claims otherwise is selling a comforting story, not science.

But — and here it becomes interesting — introverts often seem cleverer. And that is an entirely different thing. It isn’t about how clever they are, but about how they come across. Why is that?

They often think before they speak. Introverts process information more inwardly before they say anything. So what they do say tends to sound considered — not because it’s cleverer, but because it has had longer to ripen in the head before it came out.

They observe more than they talk. Someone who watches and listens a great deal notices things others miss. That looks like wisdom. Often it is simply attention — the introvert was quiet enough to see what was really going on.

They prefer depth to breadth. Introverts often favour one deep conversation over ten shallow ones. That makes their conversations seem weightier. Not because they know more, but because they would rather go deep.

Is there anything to see in the brain itself? Cautiously, yes — but differently from what’s often claimed. You sometimes hear that introverts have “thicker frontal lobes” — but that isn’t well founded; brain-scan research gives no clear picture there, and some studies actually link parts of the frontal cortex to extroversion instead. What has been measured cleanly: using PET scans, researchers found that introversion is associated with more blood flow to the frontal “thinking regions” of the brain, even at rest (Johnson et al., 1999). So the introvert’s brain isn’t “bigger”, but more active on the inside — fitting with the tendency to think things over before acting.

But mind the honest flip side: all that thinking has a shadow — it can tip over into brooding. And here’s a nuance that often goes wrong: in research, the sensitivity to anxiety and low mood is bound up mostly with a different trait, neuroticism, and not so much with introversion itself. An introvert is therefore not automatically a worrier. But someone who thinks deeply inward and scores high on neuroticism can fall into that trap. No single trait is purely a gift.

Is the world run by extroverts?

This is a question that occupies a lot of people, and the answer is: partly true, but more nuanced than it looks.

The American writer Susan Cain wrote a famous book about this, Quiet (2012), in which she describes what she calls the “extrovert ideal”. In many Western cultures — especially in schools and businesses — extroverted behaviour is rewarded: the person who is loud, talks quickly, presents themselves well and fills the room often gets more attention, more opportunity, more recognition. The quiet, thoughtful person is sometimes overlooked, even when they have valuable things to say.

In that sense it holds true: our culture is built, in large part, on a preference for extroversion. Meetings reward whoever speaks loudest, not always whoever has the best idea. Classrooms reward whoever puts their hand up, not always whoever thinks the deepest.

But reality is richer than “extroverts rule”. Many of the most influential people in history were in fact pronounced introverts: thinkers, scientists, writers, and even leaders who drew their strength from thoughtfulness rather than noise. Research into leadership even shows that introverted leaders achieve better results in certain situations — especially with teams of proactive, self-directed people, because they listen better and are less inclined to pull everything towards themselves (Grant, Gino & Hofmann, 2011).

So no, the world isn’t simply run by extroverts. It’s more that our culture rewards extroversion more visibly — but visibility and real influence are not the same thing. Much of what shapes the world happens in quiet: in laboratories, at writing desks, in minds that would rather think than talk.

No one is a hundred per cent one or the other

One last important point: introvert and extrovert are not two separate boxes. It is a scale, a sliding line with two extremes. Most people sit somewhere in the middle — they are sometimes called “ambiverts”. They can enjoy a party and a quiet evening, depending on the day, their mood, and their energy.

Even the most pronounced introvert has moments of extroversion, and the other way round. It isn’t about a label that pins you down forever. It’s about a leaning — a direction you naturally tilt towards, especially when you’re tired or stressed and fall back on your natural state.

What this means for you

The loveliest thing this science gives you is neither an excuse nor a sense of superiority, but something practical: self-knowledge, so that you can work with your nature instead of against it.

If you notice you’re an introvert: plan in some quiet after social commitments — not because you’re weak, but because your volume dial sits high and needs time to come down. Protect your quiet hours. Choose work and relationships that allow depth over bustle. And forgive yourself for being worn out after a busy party; that isn’t unwillingness, that’s your brain.

If you notice you’re an extrovert: make sure you get enough stimulation and contact, because too much silence actually drains you. But practise too — as we discussed in an earlier article — with tolerating quiet, because your brain also needs stillness now and then, even if it feels uncomfortable.

And if, like most people, you sit somewhere in the middle: learn to recognise what you need, and when. Sometimes bustle, sometimes quiet. Listening for which of the two today is asking for is a skill in its own right.

To close

I am an introvert. An observer. Someone who would rather watch and listen. For a long time I thought this was something to overcome — that I had to become louder, more sociable, more present, in order to count in a world that rewards the loud.

Science taught me something else. My quiet nature is not a flaw I must repair. It is not a sign that I am cleverer or deeper than others — that would be a vain lie. It is simply a different way in which a brain is tuned. A volume dial set high. A brain that is a little more active on the inside, and that loves depth and quiet.

And in a world brimming with noise, perhaps there is a real need for people quiet enough to see what is really happening. Not because they are better. But because every world needs both the loud voices that set things in motion, and the quiet observers who notice what the loud ones miss.

Both. Not one above the other. Both.

Are you more of an introvert, an extrovert, or something in between? And — more importantly — are you living in a way that fits how your brain is tuned, or have you been fighting your own nature for years?

No quick answer. Just a question to carry with you.

Related reading

• Homo Erectus to Gamer
• Two Skills, Two Lives
• Your Brain Is Not an Honest Witness
• Why One Child Moves Us — and a Thousand Leave Us Cold

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Sources

• Jung, C. G. (1921). Psychological Types. Rascher Verlag.
• Eysenck, H. J. (1967). The Biological Basis of Personality. Charles C. Thomas. (arousal theory; later refined, including by J. A. Gray)
• Corcoran, D. W. J. (1964). The relation between introversion and salivation. The American Journal of Psychology, 77(2), 298–300.
• Johnson, D. L., Wiebe, J. S., Gold, S. M., Andreasen, N. C., Hichwa, R. D., Watkins, G. L., & Boles Ponto, L. L. (1999). Cerebral blood flow and personality: A positron emission tomography study. American Journal of Psychiatry, 156(2), 252–257. (via PubMed — DOI)
• Depue, R. A., & Collins, P. F. (1999). Neurobiology of the structure of personality: Dopamine, facilitation of incentive motivation, and extraversion. Behavioral and Brain Sciences, 22(3), 491–517.
• Grant, A. M., Gino, F., & Hofmann, D. A. (2011). Reversing the extraverted leadership advantage: The role of employee proactivity. Academy of Management Journal, 54(3), 528–550.
• Cain, S. (2012). Quiet: The Power of Introverts in a World That Can’t Stop Talking. Crown.