Dopamine vs. Acetylcholine and Blood Flow - Introversion vs. Extraversion

I am reposting this from the INTJ  group on Multiply.com (which is ending its social networking services in December). I won't be saving all of the posts that I wrote in the group, but this is one that I'd like to keep around to refer back to if needed.  I have back dated this post according to its original posting date.

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I'm reading a book called Introverts in the Church: Finding our place in an extroverted culture (by Adam S. McHugh) and the author spends a fair bit of time essentially explaining introverts: how they're different than extroverts, why they're different, and what that means in terms of what's reasonable to expect and what's not. As I'm reading it I keep thinking, "So that's why I do that!" and "No wonder I often feel guilty I'm not doing that." (The guilt is because the extroverted culture tells us that we should be doing XYZ and for extroverts, that XYZ is something that energizes them so they really don't understand our reticence. But for us, it just wipes us out.)

I just hit a section on dopamine and brain function differences that I think is particularly interesting. I thought I'd include a few excerpts here.

Studies of the human brain have revealed three significant physiological differences between introverts and extroverts.  First, introverts have naturally busier, more active brains than extroverts.  Though introverts look calm on the surface, our brains are bubbling with activity, and thus we require less external stimulation than extroverts.  Too much external stimulation, in fact, leads to a feeling of overwhelm.  Second, blood flows in different paths in introverted and extroverted brains. Introverts have more blood flow, but it flows in a longer, slower path than in extroverted brains.  The blood in introverted brains flows to sections that are focused on internal things like remembering, solving problems and planning.  ON the other hand, the blood in extroverted brains goes to those parts that are used for the processing of sensory experienced, what's happening externally.

Third, introverted and extroverted brains have different chemical balances.  The activities of our brains are catalyzed by neurotransmitters, which are chemical substances that transmit nerve impulses.  Extroverts require greater amounts of dopamine, a central neurotransmitter in the sympathetic nervous system. It is produced when people are active and in motion. As psychologist and author Marti Olsen Laney writes, "extroverts feel good when they have places to go and people to see," probably because they are flush with dopamine.  Dopamine takes a short path through the brain and, in stressful situations, produces an "act and react" response.  It can be credited for extroverts' ability to think and speak quickly and to thrive under pressure.  It also helps them access their short-term memory more rapidly, so their data-processing circuit is shorter and faster. 

Introverts, on the other hand, require less dopamine, and when our brains have too much, we can feel anxious or overwhelmed.  Our brains rely more on another neurotransmitter, acetylcholine, a neurotransmitter of the parasympathetic nervous system, which conserves and restores energy, producing a "rest and repose" posture.  It produces a pleasurable sensation in introverts when we are thinking and reflecting. Acetylcholine, however, cuts a longer path through the brain, which explains why introverts may have difficulty accessing words or memories quickly and why we may be slow to react in stressful situation.  Introverts often prefer writing to speaking, because writing uses a different neurological pathway in the brain than speaking does. Additionally, the slower acetylcholine tributary may produces a posture of calmness in introverts and cause us to move more slowly than extroverts, which may explain why we are often less expressive with our bodies."

Wow, that explains a lot. I've always known that I don't interview well, but I thought only the nervousness could be attributed to being introverted. Now I know that the words on the tip of my tongue and the ideas not coalescing on demand (when they all came together so well just the day before as I was planning on the talk) are all a result of stuff going on in my brain. It's kind of a relief to know it's not that I'm just a moron.