In my research, especially as I mingled with Christians on the conservative side of the spectrum, I found that many still wonder whether introversion is sinful or a distortion of God's intent for humans to be social and outwardly focused. I spend a fair amount of time in my book dispelling those myths from a theological and psychological point of view. But I have also been doing a lot of reading recently about the physiology of introversion.
Traditionally introversion has been identified by its behaviors. Martin Olsen Laney, author of the foundational book The Introvert Advantage, identified three main behavioral patterns: 1. Find energy in solitude 2. Processes internally 3. Prefers depth over breadth. In chapter 2 of my book (title and release date still forthcoming) I discuss these expressions of introversion, but I'm now adding a section that examines recent research that introversion and extroversion are actually hard wired into our brains.
Psychological and neuroscientific studies have discovered three main differences between introverted and extroverted brains:
1. Introverts have more naturally active brains than extroverts. Though introverts often have an aura of calmness on the surface, their brains are abuzz with activity. Thus, they require less external stimulation than extroverts, and too much outside stimulation can cause them to feel overwhelmed.
2. Second, blood flows in different paths in introverted and extroverted brains. Introverts have more blood flow in the brain, but it moves in a different path than extroverted blood. The blood in introverted brains flows to the areas that are focused on internal things like remembering, problem solving, and planning. On the other hand, the blood in extroverted brains flows to the areas used for processing external activities and sensory experiences.
3. Introverts and extroverts have different chemical balances in their brains. Extroverts require more dopamine, a neurotransmitter (a chemical substance that transmits nerve impulses) that is produced through motion and activity. They are less sensitive to dopamine than introverts and thus require more of it. Introverted brains, on the other hand, are dominated by another neurotransmitter, acetylcholine, which is important for long term memory and a feeling of calm. Acetylcholine is the neurotransmitter of the parasympathetic nervous system, which reacts to stress with a "rest and repose" response. Dopamine, on the other hand, produces a "fight or flight" reaction to stress.
I go into these things in greater detail in my book, but it is becoming increasingly clear that introversion is not a mere social construct or learned behavior. We act as an introverts because we ARE introverts in our genetic makeup.