The Science Behind Introversion and Extraversion


For as long as psychologists have been measuring personality traits, the line between introversion and extroversion has been continually drawn and redrawn, with thinkpiece upon thinkpiece picking apart what it means to be an introvert, extrovert, or somewhere in between.

Almost every personality inventory is concerned with where we lie on this spectrum, from the popular (though scientifically unreliable) Myers-Briggs Type Inventory, to the more scientific Big Five personality traits (which measure on a scale extraversion, emotional stability, agreeableness, conscientiousness, and openness). There is a biological reality associated with both introversion and extraversion, affecting our energy levels and our temperament, but what actually causes this difference?

It’s thought that the major difference between the brain chemistry in introverts and extroverts is the way it reacts to dopamine, the neurotransmitter that is, among other things, responsible for engaging in reward-motivated behaviours. Some of these rewards, which are deeply ingrained in the human genome, include food, money, sex and social status. Both introverts and extroverts have the same amount of dopamine available to them, and will react similarly when the brain is flooded with the chemical – becoming more talkative and more alert, for example – however the difference lies in the dopamine reward network, and its activity levels. For extroverts, this network becomes significantly more active in expectation of one of these rewards, and they become more energized as a result. Introverts, however, do not experience as an enthusiastic a reaction in these instances – rather, they become overstimulated, and feel the need to retreat and ‘recharge’ their energy levels.

There is another neurotransmitter at play in the minds of introverts and extroverts as well. Acetylcholine is another chemical linked to pleasure, but it acts when we engage in behaviours like thinking deeply, focussing intently on one thing, or reflecting on our surroundings – in other words, activities that require us to turn ‘inwards’. This is why many people find pleasure in staying in and binging shows on Netflix, or taking long walks by themselves.

Each of these neurotransmitters are linked to the sympathetic and parasympathetic nervous systems, respectively. The former, also known as the ‘fight or flight’ system, is engaged when making active, risky, or fast decisions, whereas the latter is occupied with winding down and relaxing. Both of these neurotransmitters and nervous systems are used by extroverts and introverts, but unsurprisingly, extroverts thrive on the feel-good dopamine that is released when engaging the sympathetic nervous system, whilst introverts prefer the sweet release of acetylcholine that occurs when the parasympathetic system is at play.

So why does this matter? Well, many people believe that the differences between introverts and extroverts are largely superficial, with introverts often being written off as rude or antisocial, and extroverts being seen as loud and obnoxious. However, the science behind it proves that our reactions to our environments and socialising in them are not character flaws or quirks, but very real reactions in our brains to the sensory stimuli around us. Of course, not everyone is absolutely one or the other when it comes to introversion and extroversion, with many people falling somewhere in between the two, and this helps us understand why. If it all comes down to the way our brain chemistry and networks operate, then we shouldn’t be surprised that personality traits such as this cannot be grouped into essentialist categories like ‘introvert’ and ‘extrovert’. Rather, we should embrace this new understanding of the phenomenon, and aim to move towards an understanding of personality traits that is as complex and nuanced as the human mind itself.

[Hannah Burke – @hannahcburke_]

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