Easily the most fascintaing and illuminating comparison of introversion and extroversion I’ve ever seen

The entirety of what follows is taken from the book The Introvert Advantage by Marti Olsen Laney:

On dopamine:

Whereas extroverts are linked with the dopamine/adrenaline, energy-spending, sympathetic nervous system, introverts are connected with the acetylcholine, energy-conserving, parasympathetic nervous system.

“High and low novelty seekers don’t differ in their desire to feel good—everyone likes to feel good—but they differ in what makes them feel good. High scorers need excitement for the brain to feel good. The same level of arousal makes a low scorer feel anxious. A steady predictable situation would bore a high scorer but comfort a low scorer.” Dopamine appears to play an important part in what brain pathways introverts and extroverts use and how those circuits affect their temperament and behaviour.

Novelty seekers were found to have a long D4DR gene are were less sensitive to the neurotransmitter dopamine. Therefore, they need to experience life’s thrills and chills in order to produce higher levels of dopamine. … [Low novelty seekers have short D4DR genes and are] highly sensitive to dopamine. Because they receive enough dopamine in quiet activities, they don’t needs as much “buzz” in their lives. Low-novelty-seekers tend to be reflective individuals who are perfectly content to live at a slower pace. They feel more discomfort than enjoyment from thrill seeking or risk taking. Orderly and cautious, they enjoy the comfort of routine and the familiar; thus, they don’t incur much risk. Low-novelty seekers like to see the big picture before plunging ahead, and they focus well on long-term projects. They are even-tempered, good listeners, and loyal.

The researcher discovered … introverts had more blood flow to their brains than extroverts. More blood flow indicates more internal stimulation. …the introverts’ and extroverts’ blood traveled along different pathways. …the introverts’ pathway is more complicated and focused internally. The introverts’ blood flowed to the parts of the brain involved with internal experiences like remembering, solving problems, and planning. This pathway is long and complex. The introverts were attending to their internal thoughts and feelings.

Dr Johnson tracked the fast-acting brain pathway of extroverts, showing how they process input that influences their activity and motivation. The extroverts’ blood flowed to the areas of the brain where visual, auditory, touch, and taste (excluding smell) sensory processing occurs. Their main pathway is short and less complicated. …the behaviourial differences between introverts and extroverts result from using different brain pathways that influence where we direct our focus—internally or externally.

Not only does introvert’s and extroverts’ blood travel on separate pathways, each pathway requires a different neurotransmitter. …the pathway extroverts use is activated by dopamine. Dopamine is a powerful neurotransmitter most closely identified with movement, attention, alert states, and learning. “Low dopamine also results in lack of attention and concentration, cravings and withdrawal.” Having the right amount of dopamine for your body is critical. “One way of characterizing the job of dopamine circuit is that it’s a reward system. It says, in effect, ‘that was good, let’s do it again, and let’s remember exactly how we did it.'” That is why cocaine and amphetamines are so addictive—they increase dopamine. Since extroverts have a low sensitivity to dopamine and yet require large amounts of it, how do they get enough? Parts of the brain release some dopamine. But extroverts need its sidekick, adrenaline, which is released from the action of the sympathetic nervous system, to make more dopamine in the brain. So the more active the extrovert is, the more … dopamine is increased. Extroverts feel good when they have places to go and people to see.

Introverts, on the other hand, are highly sensitive to dopamine. Too much dopamine and they feel overstimulated. Introverts use an entirely different neurotransmitter, acetylcholine, on their more dominant pathway. Acetylcholine is another important neurotransmitter connected to many vital functions in the brain body. It affects attention and learning (especially perceptual learning), influences the ability to sustain a calm, alert feeling and to utilize long-term memory, and activates voluntary movement. It stimulates a good feeling when thinking and feeling. Introverts require a limited range of not too much or too little dopamine, and a good level of acetylcholine, to leave them feeling calm and without depression or anxiety.

Introverts who [use the energy-conserving, parasympathetic nervous system] too much can become depressed, unmotivated, or frustrated about not reaching goals… They need to engage the [the energy-spending, sympathetic nervous system] to get up and out. This requires learning to regulate anxiety and over-stimulation…

Longer Introvert Acetylcholine Pathway

Reticular Activating System: Stimuli enter her where alertness is regulated. Decreased in introverts. Hypothalamus: Regulates thirst, temperature, and appetite. Turns on the Parasympathetic (Throttle-Down System: Conserve Energy) in introverts Anterior Thalamus: Relay station – sends stimuli to frontal lobe and turns stimuli down in introverts Broca’s Area: Speech area where inner monologue is activated Frontal Lobe: Where thinking, planning, learning, and reasoning are engaged Hippocampus: Attuned to the environment and relays to long-term memory Amygdala: Emotional center, where emotions are attached to thoughts in introverts

Shorter Extrovert Dopamine Pathway

Reticular Activating System: Stimuli enter here where alertness is regulated. Increased in introverts. Hypothalamus: Regulates thirst, temperature, and appetite. Turns on the Sympathetic (Full-Throttle System: Expend Energy) in extroverts Posterior Thalamus: Relay station – sends increased stimuli to amygdala Amygdala: Emotional center, where emotions are attached to actions in the motor area in extroverts Temporal and Motor Area: Movement connects to working memory (short-term). Also the center for learning and processing sensory and emotional stimuli

Introversion

Introverts walk around with lots of thoughts and feelings in their heads. They are mulling—comparing old and new experiences. They often have an ongoing dialogue with themselves. Since this is such a familiar experience, they may not realize that other minds work in different ways. Some introverts aren’t even aware that they think so much, or that they need time for ideas or solutions to “pop” into their heads. They need to reach back into long-term memory to locate information. This requires physical space to let their feelings and impressions bubble up. During REM sleep or while dreaming, this pathway integrates daily experiences and stores them in long-term memory, where they are filed in may areas of the brain. Introverts are in a constant distilling process that requires lots of “innergy”.

Acetylcholine also triggers the hypothalamus to send messages to the parasympathetic nervous system to conserve energy. This system slows the body down, allowing introverts to contemplate and examine the situation. If a decision is made to take action, it will require conscious thought and energy to get the body moving. This explains why many introverts can sit for long periods while they are concentrating. Acetylcholine also rewards concentration by giving [hits of happiness] but doesn’t give the charge of glucose and oxygen (energy) to the body. The introverted process results in behaviour affecting all areas of the introvert’s life.

The introvert brain has a higher level of internal activity and thinking than the extroverted brain. It is dominated by the long, slow acetylcholine pathway. Acetylcholine also triggers the parasympathetic nervous system that controls certain body functions and influences how introverts behave.

The fact that introverts’ brains are buzzing means that introverts are likely to:

Be absorbed in thought

Avoid crowds and seek quiet

Reflect and act in a careful way

Lose sight of what others are doing

Not show much facial expression or reaction

Get agitated without enough time alone or undisturbed

Proceed cautiously in meeting people and participate only in selected activities

Reduce eye contact when speaking to focus on collecting words and thoughts; increase eye contact when listening to take in information

Surprise others with their wealth of information

Shy away from too much attention or focus on themselves

Keep energy inside, making it difficult for others to know them

Appear glazed, dazed, or zoned out when stressed, tired, or in groups

The dominance of the long acetylcholine pathway means introverts:

Hesitate before speaking

May start talking in the middle of a thought, which can confuse others

Have a good memory but take a long time to retrieve memories

Can forget things they know very well—might stumble around when explaining their job or temporarily forget a word they want to use

May think they told you something when they just have thought about it

Not offer ideas freely; may need to be asked their opinion

Are clearer about ideas, thoughts, and feelings after sleeping on them

May not be aware of their thoughts unless they write or talk about them

The activation of the parasympathetic nervous system means that introverts:

May have trouble getting motivated or moving; might appear lazy

May be slow to react under stress

May have a calm or reserved manner; may walk, talk, or eat slowly

May need to regulate protein intake and body temperature

Must have breaks to restore energy

Traits of introverted children:

Watch and listen before joining an activity

Concentrate deeply on subjects of interest

Enjoy time alone in their room, energized by introspection

Speak after thinking things through

Have a strong sense of personal space and dislike people sitting too close or coming into their room without knocking

Be private and may need to be asked what they are thinking and feeling

Need validation; may have irrational self-doubts

Talk a lot if the topic is interesting, or if they are comfortable with the people

Extroversion

Extroverts are alert for sensory and emotional input. When they get stimuli, they can answer quickly because the pathway is rapid and responsive. Their short-term memory is on the tip of their tongue, so while the introvert is still waiting for a word, the extrovert has spit out several. Extroverts need more input to keep their feedback loop working. Their system alerts the sympathetic nervous system, which is designed to take action without too much thinking. It releases adrenaline, blood (oxygen) to muscles and glucose, thus flooding the body with energy. The release of neurotransmitters from various organs enters the feedback loop, sending components back to the brain to make more dopamine. Dopamine and adrenaline release [hits of happiness] from the “feel good” center. No wonder extroverts don’t want to slow down.

For introverts, all that adrenaline and glucose soon leaves them feeling wiped out. It is too stimulating, consumes too much fuel, and leaves them with their fuel tank empty. Since they don’t get as many [hits of happiness] from dopamine and adrenaline, and acetylcholine isn’t increased in this feedback loop, they don’t receive the same good feelings extroverts do from this side of the system.

The extroverted brain has less internal activity than the introverted brain. It scans the external world to gather stimulation to fuel the shorter, quicker dopamine pathway; the signals from the brain travel to the sympathetic nervous system that controls certain body functions and influences how extroverts behave.

The fact that extroverts’ brains are constantly seeking new input means that extroverts are likely to:

Crave outside stimulation; dislike being alone too long

Increase eye contact when speaking to take in others’ reactions, decrease eye contact when listening to notice what’s happening in the environment

Enjoy talking—and be skilled at it; feel energized by attention or the limelight

The dominance of the short dopamine pathway means that extroverts:

Shoot from the hip, and talk more than they listen

Have a good short-term memory that allows quick thinking

Do well on timed tests or under pressure

Feel invigorated by discussion, novelty, experiences

Make social chitchat easily and fluidly

The activation of the sympathetic nervous system means that extroverts:

Act quickly under stress

Enjoy moving their bodies and exercising

Have high energy levels, not need to eat as often

Be uncomfortable if they have nothing to do

Slow down and burn out in mid life

Traits of extroverted children:

Be gregarious and outgoing, except during normal developmental stages

Be energized by interactions and activities

Want to tell you all about their experiences and ideas immediately, covering lots of topics

Think out loud. They’ll walk around the house saying, “Where’s my ball?” or “I’m looking for my walkie-talkie” as they hunt for these items. They need to talk in order to make decisions.

Prefer time with others than time alone

Need lots of approval. For example, they need to hear what a good job they are doing or how much you like their gift.

Like variety and are easily distracted

Often volunteering what they are thinking and feeling

On social anxiety:

Rather than being self-centered, introverts are often really the opposite. Our ability to focus on our internal world and reflect on what we are feeling and experiencing allows us to understand the external world and other human beings better. What appears to be self-centeredness is actually the very talent that provides the capacity to understand what it’s like to put ourselves in someone else’s shoes. Extroverts are also focused on the self, but in a different way. Extroverts like socializing and require the company of other people, but it’s as much about the need to be stimulated – engage me, challenge me, give me something to react to – as it is to feel related. Since extroverts don’t generate as much internal stimulation as introverts do, they need to get it from outside.Maybe this is why extroverts put introverts down – we annoy them because they feel we are withholding, and we threaten them because we don’t shoot the breeze or socialize in the way they need.

Introverts aren’t unsocial – they are just social in a different way. Introverts need fewer relationships, but they like more connection and intimacy. Since it takes a great deal of our energy to engage with other people, we are reluctant to need to spend too much energy on socializing. That’s why we don’t enjoy idle chitchat. We prefer meaty conversations, which nourish us and energize us. Energy conservation is also why we are very interested in other people but sometimes prefer to observe others rather than join them.

Extroverts, being the majority, influence the entire cultural view of introversion. Extroverts’ verbal ease intimidates introverts, making it even easier for them to conclude that they shouldn’t speak. Introverts can appear cautious or passive to extroverts. Extroverts are so used to speaking off the top of their heads that they may be distrustful of more reticent introverts. When introverts speak with hesitation, extroverts may feel impatient: Just spit it out, they think. Why don’t you have more confidence in your own opinion? What are they trying to hide? Extroverts may experience an introvert as withholding information or ideas.

When introverts appear reluctant to speak or speak slowly, they often don’t engage extroverts. Extroverts may think (and introverts can think this, too) that introverts don’t have anything to contribute. Introverts dislike interrupting, so they might say something softly or without emphasis. Other times comments made by introverts have more depth than the general level of the conversation; because this may make people feel uncomfortable, they ignore the comment. Later another person may say the same thing and receive a great response. The introverted person feels unseen. It’s frustrating and confusing for them.

From the outside, many introverts give no hint about the mental gears grinding and meshing inside. In social situations their faces may look impassive or uninterested. Unless they are overwhelmed or they are really disinterested (if the topic is too lightweight), they are usually just thinking about what people are saying. They will share their thoughts if asked. People in the group may start to exclude introverts if they don’t keep eye contact and don’t give clues that they are listening.