As mentioned above, the introvert-extrovert scale is based on things like sociability and where you get your energy from. At one end of the spectrum, introverts prefer quiet, reflective time alone, while extroverts prefer connecting with others, expressing themselves, and focusing outward.

Introverts also feel drained after spending time with people (especially large groups), while extroverts thrive here and will feel drained after spending too much time alone.

Research has also pointed to a brain explanation for why some people are more introverted than extroverted. namely one study1 found thicker areas in the prefrontal cortex of introverts compared to extroverts—the part of the brain involved in things like planning and decision-making, which may explain why introverts tend to be more reserved while extroverts tend to be more impulsive.

“Of all the different personality traits, introversion and extroversion are among the most heritable,” says Page, adding that environmental factors, such as how you were raised, will also play a role.

Our DNA also determines the degree to which we can be flexible in these traits, he says. “Introversion and extroversion are really related to a whole bunch of problems with our neurotransmitters, and the most important one is dopamine,” he says.

Dopamine feeds our brain’s reward center, and Page explains that extroverts tend to appreciate or be motivated by these dopamine hits. “But introverts,” he notes, “their brains are less driven by the need for dopamine and the excitement of dopamine.”

And this phenomenon was confirmed by research, p research 2 showing that extroverts have a stronger reward response and dopamine response to reward than introverts, highlighting that extroverts tend to seek more dopamine hits and also supporting the aforementioned impulsivity idea.

As you can imagine, where you fall on the spectrum can manifest itself in many different areas of your life, from how you approach friendships and dating, to how you do your best work, to what you prefer spend time.

If you’re still not sure if you’re an introvert or an extrovert, here’s a test to find out.