The Neural Mechanisms of Introversion and Extraversion: What Happens in the Brain?

To the introverts, extroverts revel in chaos; to the extroverts, introverts waste their entire lives with their nose in a book.

Introversion and extraversion are perhaps the two most commonly discussed psychological constructs of all time. We use them as a sort of summary statement of another person, as a blanket term that somehow describes the gist of who they are.

We’re all familiar with the stereotypical cases: the introvert who is quiet and shy, who keeps to themselves, and who prefers solitary activities. And then there’s the loud, boisterous extrovert: the one who thrives on excitement, on the energy of others, who lives to seek new experiences and friendships.

Of course, some of us teeter on one side of the spectrum, while others fall smack in the middle—these are our self-righteous “ambiverts” (who have spent way too much time thinking about the whole thing) who claim to fall perfectly between the two extremes.

As notorious as this psychological construct is, there is a significant chunk of it that is missed entirely by the mainstream media and even science itself: and that is the little-known role of our neurology in determining on which side we fall.

We’ll explore several different neurological differences between introversion and extraversion. But if you’re off to a party and you want to impress (or annoy) people, quickly memorize the following: there are varying levels of activity in the prefrontal cortex; we can change personality when we damage the brain; and if you are going to a party, you are probably an extrovert, and you are probably a happier human, too. Don’t shoot the messenger (or blogger, in this case).

The Prefrontal Cortex of the Brain

Introversion and Extraversion: What’s going on in the brain?

Differences in Activity in Key Brain Regions

Neuroimaging (i.e., brain imaging tools, such as electroencephalography (EEG), functional MRI (fMRI), and positron emission tomography) has demonstrated that extraversion is associated with activations in the anterior cingulate cortex, dorsolateral prefrontal cortex, middle temporal gyrus and the amygdala. Whereas the physiological basis of introversion includes an inhibition in the orbital frontal cortex, the medial septal area and the hippocampus.

Cortical Lesions Change Personality

Perhaps the most compelling evidence of brain-based differences in personality arise when the same person undergoes damage or a lesion to their brain. We don’t always have to cut the brain to see personality changes: we can just administer drugs that mimic the effects. Interestingly, we see that certain drugs that mimic damage to regions of the brain (the prefrontal cortex specifically) that are associated with higher trait introversion produce extraverted behaviour. One such drug is amytal (amylobarbitone).

“But consider the significance of two of the major experimental facts known about the physiological basis of introversion: (1) that the barbiturate drugs (in particular, sodium amylobarbitone) and alcohol have an extraverting effect on behaviour (Eysenck, 1967), and (2) that lesions to the frontal cortex have a similar effect (Willett, 1960)”

Introverts Have More Complex Cognitive Processes

One interesting study has shown by measuring Event-Related Potentials (ERPs) in introverts and extroverts that the P300 wave is greater in amplitude in introverts. The P300 wave is the hallmark electroneurophysiological measure of complex cerebral processes, and is indicative of processes underlying decision making, information processing, and attention. According to Eysenck’s (1967) personality theory of introversion and extraversion, introverts are thought to have higher resting cortical activity (more brain activity) compared to extroverts. Thus, they should ostensibly be more sensitive to low-intensity stimulation than extroverts.

“In Eysenck’s theory extraversion-introversion is associated with the arousal level—extraverts have a low arousal level, whereas introverts have a higher arousal level. Consequently, introverts have higher anxiety, emotionality, neuroticism, and impulsiveness (Eysenck, 1967).”

Ortiz & Maojo, 1992

As always, it behooves us to keep in mind an important caveat: the directionality problem that arises when discussing differences in the brain.

Which came first?

Do structural changes occur in the brain as a result of who we are, or are we who we are because of the differences in structure? Are certain neurotransmitters less active because our thoughts and behaviours cause them to be, or are our thoughts and behaviours a certain way because of the activity of neurotransmitters? Nevertheless, neuroscience (and other sciences for that matter) would cease to be if we insisted on infallible evidence.

Are Extroverts Happier than Introverts?

Personally, I’m an introvert, so I’ll reiterate my prior warning: don’t shoot the messenger. But if we’re being honest, fellow introverts, we know the following is true.

Introversion has been consistently associated with neuroticism, anxiety, depression, and negative affect (negative mood). Conversely, extraversion has been associated with positive affect (negative mood), But it’s not so simple—why does this pattern arise? Is it because extraverts attend more “banging” parties? Do people still say “banging”?

Extroverts may attend more parties because they have different expectations of the world based on prior experience, which creates this positive feedback loop of positive experience -> positive emotions -> repeat it -> more positivity -> extraverts are happier and shinier and probably better.

And what about introverts? Well, introversion leads to inhibitory behaviours, which could lead to a negative feedback loop of sorts. Negative experience -> withdraw further -> do not seek new experiences -> negative mood. But I’m just speculating. There are many complex reasons: extraversion is also highly heritable, as is introversion—so we can’t leave genetics out of it, either.

Are you an introvert, extrovert, or self-righteous *ambivert*? Let us know in the comments below ⬇

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