Introverts: The Thriving Brains Behind the Quiet Confidence

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Despite the fact that we are all ambiverts first and foremost, the truth is that there are a few real biological differences between those who skew more one way than the other. Nature and nurture both have a part to play here. If you have to psych yourself up for a big party or networking event, you can do that and act the part for as long as you need, but you’ll probably be exhausted for the next day and a half. We might call this regressing to the mean or compensating for extreme exertion. Try as we might, sometimes we just can’t change how we’re biologically wired. While factors including self-confidence, comfort with your social group, and health can all play roles in how you feel as a result of interactions with the people in your life, whether or not these interactions are a source of energy for you or a tax on it is largely predetermined by your brain structure. In this chapter, we explore all the biological bases for differences in this aspect of personality. The differences generally have to do with how the brain perceives stimulation and then how it handles it.

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vel thinking and analysis. In: 2012

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In other words, the prefrontal cortex of introverts is more developed in exactly the way you would expect—introverts emphasize planning, analysis, focus, and introspection, and therefore, they have developed greater brain mass suited for that. It’s not without its negatives, as these inhibit things like spontaneity, letting go of stress, and generally being more carefree. Buckner’s findings act to reinforce many of the stereotypes we hold about each of these personalities. You’ve probably heard the phrase “live in the moment” or one of its variations throughout your life. We’ve accepted this as something to strive for and an important part of being happy and living life to the fullest. It means you are being brave and not letting yourself be held back by others or yourself. As it turns out, your propensity to “live in the moment” may be correlated with how you recharge your social energy and the corresponding density of brain matter in your prefrontal cortex. Introverts, meanwhile, may often struggle to live up to this societal ideal.

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Because of their denser prefrontal cortexes, introverts dedicate more mental resources to abstract pondering, planning, and decision-making, all activities that are decidedly absent from the idea of seizing the day. This reinforces Jung’s proposal that introverts feel that the real world exists in their head. Accordingly, this also reinforces Jung’s proposal that extroverts feel that the real world is what their environments show them. As they don’t dedicate as many neural resources to analyzing and decision- making, extroverts are able to respond more to their environments and simply react without thinking. They find it much easier to live in the moment, as their brains predisposition them to react to their environment as opposed to analyze, plan, focus, and ruminate as the introvert brain structure does. Being spontaneous is something that simply happens naturally, rather than intentionally. It’s not to say that extroverts don’t think about consequences or are careless in making decisions; they just aren’t innately wired to pause, think, and analyze first. The increased prefrontal cortex of introverts also explains why they grow socially fatigued more quickly—because there is always cognitive work occurring in response to stimuli.

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is skills (Kenneth Abernathy,: 2010

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We have a clear picture of what a drunk person looks and acts like. Some people say that alcohol frees you to act like the person you’ve always wanted to be, but most commonly, alcohol causes introverts to act more like extroverts! Alcohol is not just used by people who need or want to be looser in their social interactions. Even individuals who are already highly extroverted may still enjoy alcohol, chiefly because they get to enjoy the presence of others and living in the moment to an even greater extent than usual—yet another example where, for many extroverts, more is better.  For those introverts who are searching for an escape from the feeling of being trapped inside their own heads as they analyze and introspect, unable to live in the moment, meditation can also achieve similar results to alcohol. Specifically, meditation has been shown to weaken connections between the amygdala—the part of your brain responsible for your emotions—and the prefrontal cortex (Joshua Grant). This gives you greater control over your thoughts because they are less tied to your emotional states. Imagine that you are stuck in your head using the illustration of a hamster frantically running on his wheel. This allows you to relax and approach your thoughts —actually, to separate yourself from your thoughts, function better, and prevent yourself from getting stuck in your head.

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mes from a study conducted in: 2013

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Based on previous human and animal studies, the researchers expected that the subjects’ association of the environment with a positive experience—in this case, the extra dopamine releases caused by taking Ritalin—would result in faster movement, better memory and visual attention, and a more positive demeanor. Extroverts who had taken Ritalin for the first three days of the study didn’t show significant changes in subconscious traits when watching the films without the drug, and extroverts from the control group likewise did not react differently when the placebo was removed. This was precisely the result the researchers expected. The phenomenon at play for the extroverts who had been part of the Ritalin group is called associative conditioning. By stimulating the participants’ dopamine release/reward system for the first three days with Ritalin, when the fourth day came around, the extroverts in the group had been conditioned to associate contextual cues in the lab with the reward they were expecting, even when that reward was no longer present. This is just like Ivan Pavlov conditioning his poor dog to salivate, even when the food wasn’t present. As for the introverts? The control group showed no change when the placebo was removed, as was expected. When the researchers tested introverted subjects from the group that had been administered Ritalin, however, they found that the introverts showed little to no evidence of associative conditioning.

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After three days of experiencing elevated dopamine levels while watching the videos, removing the source of dopamine also removed all of its associated behavioral and demeanor changes. What does this mean? Extroverts rely on their environment, while introverts do not. Extroverts are more sensitive to changes and use their immediate surroundings to orient themselves. Of course, we know that introverts are stuck in their prefrontal cortexes, for better or worse. The research team at Cornell showed a crucial difference between the ways introverts and extroverts process stimulation, specifically feelings of excitement. The positive feelings and enjoyment of the videos experienced by the extroverts who received Ritalin were associated with their immediate environment, whereas introverts had milder reactions, or even no reactions at all, to the videos because they associate the same feelings of reward with inner thoughts or possibly even interpreted the feelings of reward as anxiety. As one of the authors of the study, Richard A. Depue, put it, “At a broader level, the study begins to illuminate how individual differences in brain functioning interact with environmental influences to create behavioral variation."

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For introverts, internal cues have a much stronger impact on state of mind than environmental influences and reward cues do. That’s why the associative conditioning effects of Ritalin were only evident in extroverts, as it didn’t translate into reward or motivation for the introverts. Let’s take Helen, an elderly Alzheimer’s patient, as an example of how powerful associative conditioning can sometimes be. Helen was an extrovert through and through—a loud and proud Italian woman—whose decade-plus- long battle with dementia eventually led to her passing away. In the last couple years of her life, Helen forgot almost everything and everyone she had ever known, and it became increasingly difficult to help her feel happy and comfortable. When all else failed, though, there were still a couple things caregivers could do to help put her in a more positive mood. One such tactic was to put on a DVD of her favorite television show, Columbo, an old detective show with episodes usually running well over an hour. Her short-term memory lasted a matter of mere minutes in those latter days, but she would still sit through the entire episode, chuckling at Detective Columbo’s catchphrases and getting excited when he caught the murderer at the end—even though she couldn’t follow along with the plot or even remember the name of the show.

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Through decades of watching and loving the show, the associated feelings of happiness and comfort had become deeply conditioned in her psyche to the point that even when her brain had deteriorated, the associative conditioning remained. We can only wonder how Helen’s final years may have been different if she was highly introverted instead. Based on the findings of the associative conditioning study, it’s quite possible that her caregivers would have been even more helpless to do anything to improve her quality of life. Such is the power of how we process stimuli. This study, along with the previous study on introverts having thicker prefrontal cortices, reinforces our earlier conclusion that extroverts live more in the moment than introverts do. While introverts are analyzing more and responding to internal stimuli, extroverts are relying more on instinct, which results in their surroundings having a greater influence on what they are currently seeing and feeling. We can certainly learn a lot about a person by studying what motivates them—what rewards and stimulation they seek for themselves. For extroverts, these rewards may often be things such as making more positive connections, having adventures, and being positively stimulated by their environments.

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ducts of our subconscious. In: 1999

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It meant they preferred to interact and talk to themselves than to others because of how inward their brains had been wired. Again, this brain activity points to the typical behavior of an introvert. Extroverts had more blood flow into the anterior cingulate gyrus, temporal lobes, and posterior thalamus—brain areas involved with interpreting sensory data. Extroverts also had less blood flow to brain areas associated with behavioral inhibition. Therefore, they are focused on the activities of their surroundings and the people in them and don’t think about limiting or censoring themselves. Their brains are designed to choose the greatest impact of activity for raising their arousal levels. Again, it explains why extroverts tend to be outgoing and can easily strike up conversations with anyone. They are focused outwards, while introverts are focused inwards.

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All the research certainly shows a clear separation between introverts and extroverts. On one hand, you have someone who seeks out stimulation from the environment and people because it’s as if they are wearing earplugs. On the other hand, you have someone who, in the same environment and social interaction, feels like they are wearing hearing aids. Brain Chemicals 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.

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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?

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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.

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roverts (Scott Barry Kaufman,: 2014

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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.

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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.

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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.

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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.

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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?

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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.

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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.

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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.

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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. Background Noise Hans Eysenck, the researcher that coined the term ambivert, also found that the brains of different personality types had different baseline levels of cortical arousal—the degree to which our minds are in motion and being stimulated, the level of static perpetually present. High cortical arousal is perhaps best illustrated by imagining your brain activity when you are unable to sleep.

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top functioning at a level of: 1000

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o much closer to the limit of: 1000

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Moreover, it takes a larger number of stimuli because of their blunted reaction to dopamine. Make no mistake: it’s not necessarily a positive aspect for the brain of an introvert to have a greater baseline level of arousal. It doesn’t mean they are constantly at a higher level of cognitive performance. Would you say that someone who is more easily stressed out is lucky and should be characterized as smarter? No—you would see it for what it is: a trait that has both negative and positive connotations. This also doesn’t mean extroverts aren’t aware of their surroundings and capable of constant thought. What does this difference in baseline arousal mean for us? Sometimes, we just can’t help how we are wired.

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Introverts have to pace themselves a bit more and make sure to keep their average usage rate lower because they are starting from a different point than extroverts are. As always, alone time is one of the best tools for regulating their levels of arousal and ensuring they don’t become overwhelming. Extroverts have more leeway in social situations, which leads them to enjoy those situations more. The reticular activating system (RAS) acts in a way that confirms Eysenck’s findings in a major way. The RAS is responsible for regulating your levels of alertness and arousal. Assuming all humans need some type of arousal in their day, it explains why extroverts tend to act out or look for conversation with other people. On the other hand, introverts have a high level of activity in the RAS. They don’t require any other stimulation to keep them going. Studies have also found that the RAS can measure your baseline levels of arousal and even predict how much of an introvert or extrovert you would perceive yourself to be.

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If you have an active RAS, you are likely to respond in a greater way to external stimuli. That sounds curiously like the description of the introvert we have talked about multiple times in this book. Eysenck devised what was imaginatively called the lemon juice test. The theory was that if someone’s RAS was more sensitive and had a higher amount of activity, lemon juice squirted onto someone’s tongue would produce more saliva than someone who had a less sensitive RAS.  In other words, the more saliva someone produces, the more likely they are an introvert because of an increased level of arousal and reaction to external stimuli. As Eysenck predicted, the introverts in the studies produced 50% more saliva than the extroverts. Introverts might just have a higher sensitivity to everything that comes their way. The fact that something as small as drops of lemon juice can trigger massively different levels of reaction demonstrates the significance of baseline levels of arousal. A drop of lemon juice is nothing compared to a wild, raging party and meeting 20 new people.

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This puts the introvert in a totally different and more sympathetic light. What the extrovert might barely feel, the introvert might feel at a magnification of ×100. Just think of the introvert and extrovert at a party. A simple conversation is going to have a bigger impact on the introvert because of their increased level of baseline arousal. It functions on the same principle as the lemon juice. Extroverts require a much larger stimulus to react and therefore would require far more lemon juice to produce the same amount of saliva. Another helpful analogy is to compare extroverts to a steel wall and introverts to a glass window. Obviously, it is going to take less impact to break the glass window, and thus, introverts are more sensitive because of their inherent build.

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How Did Introverts Survive Evolution? In our fast-paced, competitive society, it’s easy to imagine that the social fragility of introverts is a fatal character flaw. These biological differences can lead to a vision of an early hominid that was fearful, easily spooked, and generally a pushover. This translates into the modern day as well. Here’s the thinking: extroverts get all the toys because they’re able to interact with other people more successfully and are more aggressive about getting what they want. Introverts, on the other hand, are perceived as being shy and less likely to enjoy the advantages of the world because they don’t always mix with others. Growing tired of social interaction is so undesirable as a trait that pharmaceutical companies produce drugs for people to conquer it. This thinking might cause those of us who muse about Darwinism and survival of the fittest to wonder, “If introverts are resistant or unable to be assertive about getting the spoils, how did they make it this far on earth?

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They should have been swallowed up by T. Rex long ago!" But science suggests that not only did introverts’ tendencies not get them killed, but they may have helped them survive. Biologists who specialize in evolutionary theory divide the animal kingdom into two categories: “rovers” and “sitters.” These labels correspond to an animal’s tendencies in regard to moving about in the world. Rovers are the bold ones. They’re eager to examine the immediate landscape and explore the outer edges of their environment. Rovers are the ones who go out and kill for food and bring it back to their households. They’re the type-As in their circles or groups. They go seize what they want. Sitters, on the other hand, are in no hurry to venture out of their caves.

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They patiently wait until there’s really nothing going on outside before they leave. They’re content to sit at home and let the rovers bring home take-out food. Sitters couldn’t care less if they don’t jump all over the savannah, participate in hunting, or get a spot on Animal Planet. Let the rovers get the spotlight. So in our rush to toss out labels in the animal kingdom, we’d call the rovers more likely to be bold about entering society and therefore more likely to survive and adapt than the reclusive, overcautious sitters. But here’s the thing: rovers are also the first in line to get savagely eaten. Sure, they may be bold and unafraid to walk freely in the wild. But that leaves them open to predators who have been hiding in the background, patiently waiting for some poor roving sucker to cross their line of vision.

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When that happens, the rover is history. Meanwhile, as the rover is being turned into a main-course meal with a side vegetable, the sitter is relaxation in their home, safe, sound, and not somebody else’s dinner. Hopefully it’s not too hard to see how this relationship translates into human extroverts and introverts. Extroverts have more fun (or at least look like they are), are friendlier, and take more risks, whereas introverts act out of an abundance of caution. They don’t jump into new situations head-first. They may appear to be sticks in the mud because they’re not aggressive about socializing. This keeps them safe and secure and out of harm’s way. There’s a dark side to extroverts, however.

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rs. A study of bus drivers in: 1963

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This helps them evolve into more careful beings, slightly more analytical about their place in the environment. Therefore, it makes them more likely to survive because of their own discretion. An effective society is made up of a reasonable balance of introverts and extroverts—rovers and sitters as well. Neither group would survive on their own. But the idea that extroverts are better equipped to preserve order than shy, secluded introverts is a common misconception. They have far more influence in the continued sustenance and preservation of society. The fact that our species is still around today is in no small part due to over-analysis, rumination, caution, and occasional paralysis to stay out of the grasp of danger. Summary: • This chapter is a look at the different biological differences that place people where they are on the introvert/extrovert spectrum.

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No matter what someone’s behavior is, it will always start from a baseline that their biology has set. • The first biological difference is that introverts have denser brain matter in the prefrontal cortex, which is where analysis, ruminating, decision- making, and planning take place. In fact, it’s where most stereotypical introverted behaviors take place. It also explains why introverts are said to be focused more on their internal worlds versus the external world— because they are literally stuck in their thoughts more than extroverts. To support this, extroverts were shown to have increased blood flow to areas involved in sensory processing, which allows them to focus on their external world. • 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.

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This leads them to seek out activities and  behaviors that generate acetylcholine, which creates feelings of tranquility and calm. • The final major biological difference is the level of background noise that is inside the introvert’s or extrovert’s mind. To put it plainly, introverts have perpetual static and chatter in their mind, which makes them more liable to overwhelm, analysis, rumination, and retreating to solitude. Hans Eysenck proved a corollary of this with his lemon juice test, in which he found that introverts were generally easier to arouse and become alert. • All of these differences make it seem like introverts are somewhat less predisposed to survival than extroverts. But the opposite is true; zoological studies have found that there are generally two groups in a society, rovers and sitters, and both are needed because they complement each other. Rovers are extroverts—thrill-seekers and out and about. Sitters are introverts—planners, analyzers, and operating in the background.

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That is to say, introverts keep themselves and the people around them safer than they might be otherwise.