Introverts’ and Extroverts’ Brains Really Are Different, According to Science

Introvert, you’re not imagining it. Those extroverts who seem so different from you? It’s because their brains are different. Here’s a quick-and-dirty guide to some key differences between introverts’ and extroverts’ brains, according to science — and let me tell you, it explains a lot.

Introverts Are Sensitive to Dopamine

Generally, why do extroverts like action, but introverts like calm?

It may have to do with two powerful chemicals found in the brain — dopamine and acetylcholine, “jolt juices” that hugely impact our behavior.

Dopamine gives us immediate, intense zaps of happiness when we act quickly, take risks, and seek novelty. Acetylcholine, on the other hand, also rewards us, but its effects are more subtle — it makes us feel relaxed, alert, and content.

One explanation for introversion vs. extroversion, according to Dr. Marti Olsen Laney in her 2002 book, The Introvert Advantage, is extroverts are less sensitive to dopamine, so they need more of it to feel happy. The more they talk, move, and seek out new faces, the more they feel dopamine’s pleasant effects.

But when it comes to us “quiet ones,” too much dopamine may make us feel overstimulated and anxious, writes Laney. However, when we read, concentrate, or use our minds in any way, we feel good because our brains release acetylcholine. Extroverts, on the other hand, hardly register acetylcholine’s gentle happiness bump.

This explains, on some level, why extroverts may seek out new and exciting situations — as well as social opportunities — while introverts would rather be at home with a good book or hang out in a meaningful way with just one other person.

From "The introvert brain explained"
From “The introvert brain explained”

Introverts Prefer a Different Side of Their Nervous System

Another difference between introverts and extroverts has to do with our nervous systems. Everyone’s nervous system has two sides — the sympathetic side, which triggers the “fight, fright, or flight” response, and the parasympathetic side, which is responsible for “rest and digest” mode.

Think of the sympathetic side as hitting the gas pedal and the parasympathetic side as slamming on the brakes.

When your sympathetic system is activated, your body gears up for action. Adrenaline is released, glucose energizes muscles, and oxygen increases. Areas of your brain that control careful, measured thinking are turned off, although dopamine increases alertness in the back of your brain.

On the other hand, when you engage the parasympathetic side, your muscles relax, energy is stored, and food is metabolized. Acetylcholine increases alertness and blood flow to the front of your brain.

Of course, extroverts and introverts use both sides of their nervous system at different times. But which side do we introverts generally prefer? You’ve probably already guessed: According to Dr. Laney, we prefer the parasympathetic side, which slows us down and calms us.


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Introverts Use the Long Acetylcholine Pathway

Ever wonder why, as an introvert, you are prone to overthinking? It has to do with how we process stimuli in a different way than extroverts do.

When information from the outside world — like someone’s voice or images on a computer screen — enters an extrovert’s brain, it may travel a shorter pathway through the brain, passing through areas where taste, touch, sight, and sound are processed.

But for us introverts, the pathway might be much longer. Stimulation travels through many areas of the brain, including:

  • The right front insular, which is an area associated with empathy, self-reflection, and emotional meaning. This is also the area of the brain that notices any errors.
  • Broca’s area, which plans speech and activates self-talk.
  • The right and left front lobes, which select, plan, and choose ideas or actions. These areas also develop expectations and evaluate outcomes.
  • The left hippocampus, which stamps things as “personal” and stores long-term memories.

This means we introverts may process information more thoroughly and deeply than extroverts do. No wonder it sometimes takes us longer to put our thoughts into words, react, or make decisions!

Introverts Have More Gray Matter

Finally, a study published in the Journal of Neuroscience found that introverts had larger, thicker gray matter in their prefrontal cortex, which is the area of the brain that’s associated with abstract thought and decision-making. Extroverts had thinner gray matter in that same area. This suggests that we introverts may devote more neural resources to abstract thought, while extroverts tend to live in the moment more.

What This Research Means

It means that as an introvert, you were probably born this way — although, of course, your background and experiences play a role in shaping you, too.

It means that once an introvert, always an introvert. That doesn’t necessarily mean you’ll never enjoy a party or seek new and exciting experiences like extroverts do, or that extroverts will never sit quietly and read a book — we still get to choose what we do. And, interestingly, there’s some evidence that our personalities change over time (for the better), including that fact that we all get more introverted as we get older.

Keep in mind that “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,” writes Dr. Laney in The Hidden Gifts of the Introverted Child.

Finally, be aware that we still don’t fully understand how personality forms or how the brain works; the explanations in this article are simply the best hypotheses we can make with the information we currently have. And some psychologists think introversion and extroversion have more to do with rewards than neurotransmitters — you can read more here.

So those loud, rowdy extroverts? Cut them a little slack. It’s their brain!

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Jenn Granneman is the founder of IntrovertDear.com and the author of The Secret Lives of Introverts: Inside Our Hidden World. Jenn is a contributor to Psychology Today, HuffPost, Susan Cain’s Quiet Revolution, Upworthy, The Mighty, The Muse, Motherly, and a number of other outlets. She has appeared on the BBC and in Buzzfeed and Glamour magazine. Jenn started Introvert, Dear because she wanted to write about what it was like being an introvert living in an extrovert's world. Now she's on a mission: to let introverts everywhere know it's okay to be who they are.