Born To Be Wild (Or Not)

As a topic I have a lot of interest in, I wanted to expand on introversion and extroversion, this time by trying to look into the biology contributing to these traits. This post is a follow-up to my previous post about the difference between introversion and extraversion, The Lonely Introvert. If you haven’t read it already, I recommend you do, as this post will read better in context. I have also now written a post on how society’s preference for extroverts can stifle the creativity of introverts: Introverts: A Neglected Creative Resource?

Are We Born This Way?

I want to start off by saying that when it comes to personality differences, it is a combination of our genetics and environmental factors which determine who we are. While genes have been linked to certain types of behaviour, these often only account for an incredibly tiny number of the differences between humans; even when a “personality gene” is found, it is often not the only gene which can contribute to this feature of personality, even when there is a strong link between this gene and the trait, and environmental factors can outweigh or alter the effects of this gene, so that in some people it may have no effect.

Do Introverts And Extroverts Have Different Brains?

A study in 2005 by Michael Cohen found that extraverts’ brains have a stronger response in two key areas when gambles they take part in pay off: these areas are the amygdala and the nucleus accumbens. The amygdala is a part of the brain associated in processing emotional stimuli, while the nucleus accumbens is part of the brain’s reward system. An important part of this system is the brain’s response to the neurotransmitter, dopamine (a small chemical which transmits signals between neurones). Amongst other things, dopamine has been linked to feelings of reward and addictive behaviours; too much dopamine has been linked to (but is not necessarily the cause of) schizophrenia, while a lack of dopamine contributes to Parkinson’s disease, hence the use of L-Dopa (a molecule which can be made into dopamine in the brain) as treatment for Parkinson’s disease.

There Are A Few Different Suggestions For How Dopamine Affects Our Personality

Previous studies found that individuals with more responsive dopamine receptors in their brains exhibit less thrill seeking behaviour: higher responsiveness to dopamine could mean an individual needs to take part in less risky activities, as they require a lower level of stimulation to achieve the same level of response, so would be overstimulated by trying new things or taking more risks (these people are therefore introverts, like the highly reactive babies I talked about in my last post).

A different study published in the Journal of Neuroscience suggested that there might be less dopamine inhibitors (molecules which prevent dopamine from having an effect) present in thrill-seekers, so their brains have more dopamine acting on them, providing them with feelings of reward. Other studies have  also found higher levels of dopamine in the brains of thrill-seekers when participating in risk-related tasks, such as gambling. More dopamine = more of a “buzz”, therefore thrill-seekers have more reason to take part in risky activities, as they gain a greater reward.

Another model, contradictory to my first suggestion, suggests that extroverts are actually more sensitive to rewards, and that this motivates them to try more new things and seek higher levels of stimulation.

We Don’t Really Know How Dopamine Is Involved, But We’re Pretty Sure That It Is

So clearly, views are quite conflicted on this topic and we’re unclear of which of these mechanisms is actually true. This is especially ambiguous, because when we say a personality trait has been “linked” to a gene or a neurotransmitter, it means that some individuals displaying the trait were found to share certain genes or biological traits – not everyone, only some. It’s also only a correlation: there’s always a chance that this “link” is just a coincidence. We do think however that at least some component of our level of extroversion is determined by our brain chemistry and it is very likely that dopamine is involved somehow. As our brain structure is partly determined by genetics, at least part of our level of extroversion is probably inherited, though it won’t be all because of one gene. Our degree of introversion/extroversion is estimated to be about 50% hereditary, so clearly genes aren’t the only players in the game. Our upbringing can influence what kind of environment we prefer to surround ourselves with and our early experiences will alter our perception of social events.

While I’ve spent hours (yes, just on this one blog post) trying to find out why I feel so overwhelmed by large crowds and too much small-talk, I simply can’t find one concrete explanation. When our brains and personality differ so greatly between one individual and another, it’s difficult to completely separate one aspect of our complex personality to be able to investigate it.  If you take one thing away from this blog post, it is that while personality is incredibly interesting to try and find the cause of, it is incredibly complicated and to put something as simple as a “personality gene” down as the cause would be a crime. Our preference for introversion or extroversion can vary even on a day-to-day basis, depending on how we are feeling. We are not set in stone.

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