It’s All In Your Head


With the advent of the fMRI, PETscans and other means of exploring previously less understood inner workings of the human brain, our understandings of introversion and extroversion have been greatly advanced. Our language, however, often still reveals our ignorance on these matters. “Stop being so introverted. You’re in your head too much; it’s depressing. Let loose, have some fun.” We might just as well ask a leopard to change his spots.

Far from being a choice or preference, introversion at one end of the continuum is actually visible in brain scans. At either extreme of the spectrum marked on one end by extroversion and on the other by introversion are two notably different biological realities. Though we’re all human, this is yet one more aspect of an amazing diversity within the species.

This article is dedicated to shedding a little light on this topic. When someone says to you, “It’s all in your head,” perhaps after reading this issue you can simply respond, “You’re right.” Of course, it’s not actually this simple. The neural differences between us are only part of what makes each one of us the complex individual that we are.
The Autonomic Nervous System

The autonomic (self-governing) nervous system controls all of those functions that we do without thinking (e.g. breathing, digesting, heart beating, etc.). It is divided into two halves that ideally should work in good balance with each other.

The sympathetic nervous system has to do with “throttling up” and preparing us for action. The parasympathetic system works in the opposite direction. It has to do with “throttling down” and restoring the body after action.

These two halves of the autonomic system each have important functions that each of us needs. It appears to be the case that balance in this regard is often lacking on either extreme of the temperament spectrum. Extroverts tend to favor the sympathetic side while introverts favor the parasympathetic. This may be a good argument for the superiority of ambiversion as a well-adjusted and well-balanced point between these two complimentary systems. The table below shows the yin and yang of the autonomic system

The Long & Short Neural Roads

Consistent with a leaning toward either side of the autonomic system is a difference between introverts and extroverts that can be observed in their typical neural pathways. All of us begin with an external stimulus that comes into our brain at the point of our reticular activating system. From there, things diverge into two paths:

For the extrovert:


1. Reticular Activating System

2. Hypothalamus – turns on full throttle system (adrenaline, dopamine)

3. Posterior Thalamus – increased stimulus

4. Amygdala – emotions connect with actions

5. Temporal & Motor Area – movement, short-term memory


For the introvert:


1. Reticular Activating System

2. Hypothalamus – turns on throttle down system (acetycholine)

3. Anterior Thalamus – sends stimulus to frontal lobe

4. Broca’s Area – speech center, inner monologue

5. Frontal Lobe – thinking, planning, reasoning

6. Hippocamus – attuned to environment, long-term memory

7. Amygdala – feelings are attached to thoughts


For the ambivert:

Because things aren’t binary, ambiverts must be using some hybrid mixture of these two paths. Their brain activity would possibly be less strong along either pathway, using both situationally. Additional study needs to be done to more fully understand ambiverted brain pathways.

You can see that the introverted path is much longer going through the frontal lobes. This explains why introverts tend to be less able to make quick decisions and “think on their feet.” PETscans have shown that, in general, introverts have a higher base level of brain activity. When an introvert doesn’t respond, don’t assume that they aren’t thinking deeply about your question. They may well be thinking “too deeply” in their frontal lobes to respond in the moment.
Different Paths / Different Chemicals

All of us are inextricably connected to a myriad of stimuli in our environment. As it pertains to the brain, those stimuli all arrive to the brain by means of the reticular activating system. Once the stimulus hits the RAS, the paths on either end of the spectrum between extroversion and introversion diverge.

Not only are the paths different, the chemical messengers involved, the neurotransmitters utilized are different. Here are a few of the notable ones:

Dopamine: part of the reward system, motivates us to action, working with adrenaline gets us excited
Acetylcholine: associated with thinking and concentration, part of inhibitory “throttle down” system
Endorphins: endogenous morphine created by the body, opiates to mask pain, precursor to dopamine
Oxytocin: related to trust and bonding
Serotonin: related to impulse modulation, sense of calm, feelings of importance

Extroversion is far more dependent on dopamine and endorphins. Introversion relies more on acetylcholine. This is the chemical explanation for why introverts feel happier thinking and feeling as opposed to extroverts who feel happier doing and being stimulated externally.

Oxytocin and serotonin are critical chemicals for all of us. Oxytocin is the hormone released when a mother nurses. It is about trust and connection. Serotonin gives us a sense of pride, feeling connected to the tribe. These two are what Simon Sinek calls, “selfless chemicals.” They both may be hindered (especially in introverts) in an overly “selfish chemical” filled environment (a.k.a. an extrovert biased workplace). Because of this, it is critical that our workplaces are friendly to both sides of the continuum, giving a place for dopamine and endorphin drivenness that is counter-balanced with oxytocin and serotonin togetherness. Speaking of this need, Sinek says (p. 71):

“The only thing we can do it create environments in which the right chemicals are released for the right reasons . . . The goal for any leader of any organization is to find balance.”
The Big “D”

In regard to understanding introversion as different from extroversion, the most important neurotransmitter to focus on may be dopamine. Notice the differences on either end of the spectrum related to dopamine.

This explains so much. This is why introverts will tend to shut down in a way that almost looks painful in an over-stimulating environment. They’re not shy or anti-social but they may well be over-stimulated. What “feels good” for an extrovert may be painful for an introvert. They run at a higher base level of arousal and are more readily over-aroused, whereas extroverts tend to be dopamine deficient and therefore seek out stimulating experiences to increase the release of adrenaline/dopamine that makes them “feel better.” We couldn’t be more different as it relates to dopamine.
So What?

Learning about the brain is interesting, but how do we beneficially apply this knowledge to real life? Knowledge, some have said, is power. That’s the case here. Knowing what we now know about the brain, we can no longer legitimately claim that introversion is a choice any more than extroversion. We all live at different presets along the temperamental spectrum. We can adapt our behavior as we need to situationally but each of us has a natural style that is the real us. Creating environments where each one of us, introverted or extroverted, can operate from our own intrinsic strengths and be valued for our unique contributions is the key. Here are some ways we can apply this knowledge of our natural differences:

Our differences are real. We need to stop trying to change people on the other side of the continuum to be more like us.
Our differences are real. Really caring for others who are different is going to require a much deeper level of understanding and adapting. It won’t be easy.
Everyone has strengths and challenges. People who are on either end of the spectrum have greater strengths that the group needs to leverage (we need the people in the middle as well).
Valuing each other is our greatest need. We all need to belong and be valued as part of the team. Understanding the true nature of the differences helps us avoid harmful stereotypes and misconceptions.


Marti Olsen Laney, The Introvert Advantage: How To Thrive in an Extrovert World (New York: Workman Publishing, 2002).

Simon Sinek, Leaders Eat Last: Why Some Teams Pull Together and Others Don’t (New York: Penguin Group, 2014).

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