What makes someone an extrovert or an introvert?

Would you prefer to spend a Saturday night at a club or curled up in bed with a good movie? Do you prefer large gatherings or one-on-one catch ups? Do you prefer working as part of a team or on your own? These are the questions you may find yourself being asked in an attempt to determine facets of your personality. So what causes these differences between individuals?Extroversion and introversion are the two traits that these questions are likely to be assessing and while it is rare for somebody to be completely one or the other, in general people fall somewhere along the spectrum. Extroversion refers in general to people who focus their attentions on the outer world (physical and social); these people are commonly outgoing, talkative and assertive. Introversion on the other hand refers to people who focus their attentions on their inner world (thoughts, ideas and feelings); these people are in general quieter than extroverts and feel more energised from time alone. Ambiverts lie somewhere in the middle of these two spectrums.So what makes someone extroverted or introverted? If you’re an extrovert you may find yourself asking your introverted friend this very question when they want to leave a social gathering early. And if you’re an introvert you may find yourself asking your extroverted friend the same thing when it’s the middle of winter and they’d rather go out than stay indoors with a movie and the heater full blast. Well recent studies have suggested that introversion and extroversion may actually be hardwired into our brains.One study used a positron emission tomography (PET) scan to examine the blood flow in the brain of introverts and extroverts. It was found that introverts had increased blood flow in the frontal lobes and anterior thalamus, areas that are commonly involved in problem solving, planning, judgment, and recall. Extroverts on the other hand, showed increased blood flow in the anterior cingulate gyrus, temporal lobe and posterior thalamus; areas involved in processing sensory data. This provides a neurological basis as to why introverts focus their attention more inwardly and extroverts more outwardly.Other studies have further demonstrated a physiological basis to these personality traits. The reticular activating system (RAS), a structure of the brain stem that is primarily responsible for regulating arousal, has a higher level of basal activity for introverts as opposed to extroverts. For example, an introvert at a very loud, very rowdy party, surrounded with a lot of stimulation will quickly become overwhelmed and de-energised. An extrovert on the other hand in the same situation will not be as aroused as their fellow introvert and therefore enjoy highly stimulating environments more. So extroverts, next time you’re out at a bar with your introverted friend just remember your excitement may not be an exact mirror of theirs!Furthermore, when both extroverts and introverts were given the opportunity to gamble it was found that extroverts had stronger reactions in both the amygdala (the part of the brain that regulates our emotions) and the nucleus accumbens (a part of our brain involved in regulating dopamine). This suggests that extroverts find greater enjoyment in stimulating activities such as trying new things, meeting new people or taking risks. Introverts don’t appear to elicit the same reaction, which is why many introverted people prefer staying home or grabbing a coffee with a close friend to being at a club.This is not to say by any means that introverts don’t enjoy human interaction, or heading out to a party just as much as the next person; however it is important to keep in mind that different personality traits tend to thrive in different situations.