 What causes introversion and extroversion? Nature or nurture? Most people know whether or not they identify as an introvert extrovert or an ambivert. Most people have qualities of both, however, people usually tend to lean one way more than the other. Growing up, I'd have to back out of social gatherings last minute because the idea of having to look this entertain for this long was draining. As an introvert, I've always wondered why I am the way I am and not the way my best friend is. She could count the people she speaks to on a daily basis on both hands while I could only count her, my boyfriend, and my cats as the ones I interact with on a daily basis. My best friend, on the other hand, could see people every day and not get tired of their company. Why was it so hard for me, but not her? There had to be an answer as to why people lean one way more than the other on the spectrum. At first, I guessed that it would come back to the age-old debate, nature versus nurture. Truthfully, just like introversion and extroversion, nature and nurture is not black and white. We know that now, and I think we always have. It's a gray area because there's no way to say that someone's upbringing is completely due to their home lives, and there's no way to say that it's solely because of the environmental factors either. Let's say you get pushed around a few times as a kid so you grow up to be quiet and secluded because you were bullied as a child. Or you grow up to be talkative and attention seeking because you never got to be that as a child when you were being picked on. These are drastically different outcomes, so it can't be one's surroundings that make him or her an introvert. Two different possible outcomes suggest that nurture is not a soul contributor. Well, according to Hans Eisink, a psychologist from the 1960s, it's just got to do with our brain and its chemicals. You could be raised this way or that way, but as long as you've got your brain, you will be who you are despite nature and nurture. In 1999, scientists measured the blood flow of introverts and extroverts and found that introverts had more blood flow in their frontal lobes and interior thalamus. These sections of the brain are the parts that take care of remembering things, planning events, and solving problems. At the same time, extroverts had more blood flow in brain areas, anterior cingulate gyrus, the temporal lobes, and the posterior thalamus that had more to do with sensory, in this case specifically for socializing. This may be why extroverts enjoy people's company since their brains are happiest when their senses are being stimulated. Carl Jung suggests that this is why extroverts are more outward and introverts are more inward. Over decades of research for the two personality types, most scientists have come to the conclusion that it has a lot to do with dopamine in the brain. It is suggested that extroverts are less sensitive to dopamine, so they need a lot of stimulation to get enough of it. This has something to do with the amount of blood flow to certain sections of our brains. A 2012 study by Randy Buckner at Harvard University found that introverts have thicker gray matter in their prefrontal cortex, linked to thinking and decision making, than extroverts did. He says that this is probably why an introvert can thoroughly consider outcomes of a decision, while an extrovert may make one and act upon it quicker. Now, if you're asking why people have more blood flow in their frontal lobes than their posterior thalamus, I couldn't tell you. I don't think there's enough research that's been done on the biology of the human being, let alone the human brain, to explain why we are built the way we are. If you enjoyed this video and want to see more psychology videos from Psych2Go, please support us by sharing this video on your social media.