Dopamine and acetylcholine are at the heart of another difference in how introverts and extroverts process external stimuli.

Extroverts have blunted dopamine receptors, so they need more stimulation to feel pleasure.

Introverts have heightened dopamine receptors, so they feel overwhelmed more easily.

This leads them to seek out activities and behaviors that generate acetylcholine, which creates feelings of tranquility and calm.

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The next stop on our tour of the biological difference between introverts and extroverts is about the brain chemicals known as neurotransmitters.

We briefly discussed dopamine earlier, but there are multiple ones at work here.

Unlike your favorite science fiction movie, these chemical differences don’t create superheroes and villains.

The neurotransmitters largely responsible for the difference between introverts and extroverts are dopamine and acetylcholine.

Let’s tackle them one by one.

Dopamine is a neurotransmitter that everyone produces in the brain in reaction to stimuli that we encounter in the world.

Think about how we produce saliva according to whether we sense food around us.

Specifically, dopamine is released before (in anticipation), during, and after we receive pleasurable stimuli.

It is the neurochemical associated with sex, drugs, and rock and roll.

If there’s a large slice of chocolate cake about to be devoured, dopamine is going to be released.

Excited about finding a new beau?

Cue the dopamine.

Screaming on a rollercoaster?

Equal parts dopamine and adrenaline, perhaps.

When a neuron releases dopamine to another neuron, the dopamine floats through the synapse; think of the brain’s synapses as the highways between each neuron.

These are the roads that the chemicals travel through to get to the receiving neuron.

It may sound like an easy process, but our brains have countless neurons that are constantly firing.

Different chemicals are being released every second to help an individual go about their day.

So what does this all mean?

Dopamine signals pleasure, but different stimuli, situations, and individual perception can affect how dopamine is produced and distributed.

Of course, depending on the personality of the individual, dopamine is also processed differently.

It was found that when exposed to the same reward stimulus, introverts were affected more, while extroverts needed a higher degree of intensity to elicit the same feelings.

Everyone craves dopamine, but extroverts need higher amounts to feel its effects, almost like someone who has developed a tolerance for caffeine or more illicit drugs.

Therefore, to get enough dopamine to make an emotional impact, extroverts need greater or more rewards than introverts to create and process dopamine in their brains.

It’s as if the sensation has been dulled for extroverts, so they continually seek out stimuli to produce the results they crave.

This may partially explain why extroverts want to be around people and indeed are stereotypically found at the center of a party.

The more stimuli and rewards that swirl around the extrovert, the higher the chance that they generate dopamine in sufficient quantities to effectively feel pleasure.

This brings additional clarity to what the extrovert is really after.

Earlier, we discussed that they enjoy interaction though not necessarily connecting, and now we discover that extroverts are seeking adequate stimulation to feel something.

That’s reducing them to simple slaves to their brains’ needs, which is not always true, but it’s certainly food for thought as to what drives and fulfills them.

Introverts, on the other hand, are much more sensitive to dopamine.

They do not require as much attention or stimulation to receive the amount of dopamine needed to feel pleasure.

Because introverts are highly sensitive to dopamine, they may crave more alone and quiet time.

Their main task is to avoid being overwhelmed by an excess of dopamine, and thus they sequester themselves to do so.

This sensitivity to dopamine means that for introverts, there is such a thing as “too much of a good thing.” If extroverts need increasing amounts of dopamine to feel good, introverts need only subtle or small amounts.

More than that, and you’re looking at someone who wants to retreat, even if it’s from their own birthday party.

This makes even more sense if we put things back into the context of the social battery we introduced earlier.

Dopamine drains the social battery of the introvert, and thus introverts seek refuge while extroverts seek out dopamine-producing stimuli.

Additional supporting research has shown that the difference in dopamine sensitivity could be due to the number of dopamine receptors each individual has (Marti Laney).

In summary, extroverted individuals need much more dopamine to feel happy at the same level an introvert would feel from a smaller amount of dopamine.

They need to seek attention, be social, and participate in stimulating activities to release the dopamine they need.

Introverts are the opposite.

If they get too much dopamine, they feel overwhelmed and anxious.

They need more quiet time so that they are not overwhelming their dopamine receptors.

Dopamine is produced, processed, and dealt with differently in extroverts versus introverts.

Does this mean that introverts are destined for a brain that is set off by minimal amounts of dopamine or perpetually under-satisfied and on the verge of explosion?

What, then, is pleasurable for the introvert?

Imagine you have just woken up on a sleepy Sunday morning.

You go to the kitchen and make yourself a warm cup of tea.

That first sip of tea warms you from the inside out.

It makes you feel relaxed, calm, and content.

That feeling is caused by the neurotransmitter acetylcholine, which is what introverts tend to prefer.

Acetylcholine is the opposite of adrenaline.

When adrenaline is released, the body goes into fight-or-flight mode.

Your senses become heightened, your heart rate goes through the roof, and you are ready for whatever comes your way.

Acetylcholine takes you out of fight-or-flight mode.

After you finish fighting off the threat or running for your life, it is the breath of fresh air that helps you relax and brings your bodily functions back to a normal state.

It brings you to homeostasis.

In the central nervous system, acetylcholine is also used in conjunction with pleasure and rewards, though a different type of reward than dopamine signals.

Acetylcholine makes us feel good when we turn inward and can focus on fewer things with fewer people.

It makes us feel good when we are relaxed.

It should come as no surprise then that the activities introverts most enjoy release the soothing effect of acetylcholine.

Engaging in activities that are low-key, calming, and mentally challenging releases acetylcholine.

Introverted brains have been shown to have increased blood flow through acetylcholine pathways, whereas extroverts have this blood flow on their dopamine pathways (Christine Fonseca).

The dopamine pathway is also shorter than the acetylcholine pathway.

It takes longer for someone to feel the pleasure associated with acetylcholine-inducing stimuli.

This is all good and fine for the introvert who wants to be able to pace themselves, but for the extrovert?

They get bigger rewards much faster when they receive a hit of dopamine versus acetylcholine.  Since they enjoy this quick and powerful happiness boost, why would they want to look elsewhere?

They won’t—they’ll keep engaging in the types of behavior that can gain them dopamine, which are what we would recognize as typically extroverted behavior.

As you can see, seeking pleasure and the subsequent manipulation of these neurotransmitters (albeit unknowingly) can lead to very characteristic behaviors.

Introverts crave acetylcholine because it’s their most prevalent source of rewards, which are signaled by what we would recognize as typically introverted behavior—relaxed, calm, and slow-moving.

Extroverts can still reflect and be lost in thought, but this pleasurable feeling from acetylcholine pales in comparison to the jolt of dopamine they require.

Extroverts handle an onslaught of stimulation masterfully.

In fact, they thrive on and crave this stimulation that produces dopamine.

Introverts are more sensitive to dopamine and crave the rewards acetylcholine provides, which correspond to opposing types of behaviors.

Thus, extroverts need hearing aids on their dopamine receptors.

Their receptors are not as sensitive, so they need to receive that much more to get a hit.

The more dopamine they get, the better they feel.

On the opposite side of the spectrum, introverts need earplugs.

Introverts are currently walking around with mega speakers on their dopamine receptors.

Even a small amount can seem like too much.

Their receptors are different than extroverts’ in that they are more sensitive.

This all fits neatly with the social battery concept.

Extroverts fill their batteries with the people they surround themselves with.

Dopamine fills their battery up.

Introverts recharge their batteries alone.

When they receive dopamine, it can overflow and fry the social battery, and instead they seek the rewards that acetylcholine provides them with.

For introverts to be happy and thrive, they need to reduce the dopamine and increase the acetylcholine in their brains.

This leads introverts to be selective about what they do and who they interact with, and eventually they retreat into solace.

That’s why pretending to be busy for an entire weekend, when in reality you are just at home by yourself with four books, can feel so good.

If you’re an introvert, you know that you are walking around with an increased sensitivity to social situations courtesy of your dopamine tolerance.

Just don’t try to perform a pale imitation of an extrovert, because it’s not in your biology to derive happiness from those behaviors.

While blindfolds and earplugs may help, they’re not always the most practical choice.

Be selective about your social interaction and try to find what’s really exhausting you.

Make sure to recharge alone so you can bask in the sweet glow of acetylcholine, which is what will actually make you happy.

Introverts and extroverts are who they are because of these chemical differences.

It goes beyond preferences and personality; it is literally programmed into our brains.

The last major neurobiological difference is how aroused extroverts and introverts are in their natural states.