Did you know that introverts and extroverts respond differently to the naturally occurring neurotransmitters in our brains? Jennifer Granneman, from the blog Introvert Dear, recently published a wonderful piece on Quiet Revolution examining these links, and more.

Turns out, extroverts respond more to dopamine, while introverts respond more to acetylcholine. The thrill of crowds leads to thriving on dopamine; the thrill of a quiet room and solitude, however, thrives on acetylcholine.

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Another piece of the puzzle is the dichotomy between the sympathetic and parasympathetic nervous systems:

When we engage the parasympathetic side, our body conserves energy, and we withdraw from the outer environment. Our muscles relax; energy is stored; food is metabolized; pupils constrict to limit incoming light; and our heart rate and blood pressure lower. Basically, our body gets ready for hibernation and contemplation—two of the things introverts like the most.

Both introverts and extroverts use both sides of their nervous systems at different times, just like they use both neurotransmitters. But—no big shocker here—extroverts tend to favor the opposite side of the nervous system: the sympathetic side, known as the “full-throttle” or “fight, flight, or freeze” system. This side mobilizes us to discover new things and makes us active, daring, and inquisitive. The brain becomes alert and hyper-focused on its surroundings.

We’re all just responding differently to our neurotransmitters.