I've been observing my family and I've this is what I've got so far....
Me = ISTJ (Frequent use of Ne)
Mom = ISTJ (Heavier usage of Fi, but Si Te still dominate.)
Dad = ISTP
Sister = Not sure yet. Current guesses are on ISFP and ENFJ. See the following thread for details:
http://www.typologycentral.com/forums/what-s-my-type/21340-what-my-sister-s-type.html
As far as preference for nature / nuture, I think my Introversion was inherent --- I am without a doubt the most introverted member of our bunch. Not as sure about the S and T traits, but I think the J trait comes from me watching Mom, whom I was around the most growing up. She's a super-J person.
Interesting articles:
30 March 1999
Introverts At The Front, Extroverts To The Rear
by Kate Melville
A University of Iowa study adds to growing evidence that being shy or outgoing may be all in your head. Investigators looking at cerebral blood flow and personality found more conclusive signs of different brain activity in introverts and extroverts.
This is the first study to reveal the connections between activity of the thalamus and introversion and extroversion, said Debra L. Johnson, Ph.D., UI assistant research scientist in psychology and the study's lead investigator. "We found more evidence that people might be shy or outgoing because of the way their brains are structured, not because of experiences they've had."
Previous studies have shown that introversion and extroversion are based on variations in brain function, but those studies did not describe all the locations found in this study. The UI researchers examined 18 healthy individuals using positron emission tomography (PET) scans, which can provide a high-resolution image of the entire head.
The PET scans revealed that introverts have more activity in the frontal lobes of the brain and anterior, or front, thalamus. These areas are activated when a person's brain takes on internal processing such as remembering, problem solving and planning. Extroverts exhibit more activity in the anterior cingulate gyrus, temporal lobes and posterior thalamus. These areas are typically thought to be more involved in sensory processing such as listening, watching or driving.
The differences in cognitive style and sensory-processing relate to the qualities associated with introversion and extroversion. True introverts are quiet, inwardly focused and reclusive. Extroverts are gregarious, socially active and sensation seeking.
"Introverts get more of their stimulation internally, whereas extroverts seek outside sources," Johnson said. "Extremely introverted and extroverted personalities are two ends of a continuum, with most people falling somewhere in between."
Johnson added, "The implication is that one personality trait -- introversion or extroversion - isn't right or wrong. These variations in brain activity suggest that a lot of our individual differences have an underlying biological cause."
The subjects, 10 men and eight women, first took personality tests to determine the extent to which they were introverts or extroverts. The researchers later had the subjects lie down with their eyes closed while the PET scan measured brain activity.
"Lying quietly allows the mind to be free and do what it naturally does," Johnson explained. "When a part of the brain becomes active, there is increased blood flow to that region, which shows up on the PET scan."
The findings were published in the February issue of the American Journal of Psychiatry.
More Stuff:
The Introverts Strike Back
The Difference Between Introverts and Extroverts | Psychology Today
Top 5 Things Every Extrovert Should Know About Introverts
It turns out that the distinction between introversion and extroversion is all in your head — but I mean this quite literally!
brain activityIntroverted children enjoy the internal world of thoughts, feelings and fantasies, and there’s a physiological reason for this. Researchers using brain scans have found introverts have more brain activity in general, and specifically in the frontal lobes. When these areas are activated, introverts are energized by retrieving long-term memories, problem solving, introspection, complex thinking and planning.
Extroverts enjoy the external world of things, people and activities. They have more activity in brain areas involved in processing the sensory information we’re bombarded with daily. Because extroverts have less internally generated brain activity, they search for more external stimuli to energize them. [emphasis added]
The social gene
The question remains, “How do we get to be an introvert or extrovert?” While nothing is “all in the genes,” there appears to be a genetic factor in our socializing preferences. The “novelty-seeking” or lust for excitement may be linked to a D4DR gene on chromosome 11. Dean Hamer, chief of gene structure and regulation at the National Cancer Institute in Bethesda, Maryland, studied the D4DR gene and found that it affects the neurotransmitter dopamine, which controls excitement levels and is vital for physical activity and motivation.
Novelty seekers (where’s the bungee-jumping party?) were found to have a long D4DR gene and were less sensitive to dopamine, a chemical mediator for pleasure and emotion in the brain. The “low-novelty seekers” had short D4DR genes that were highly sensitive to dopamine. Because they receive enough dopamine in quiet activities, they don’t need as much “buzz” in their lives. They feel more discomfort than enjoyment from thrill-seeking or risk-taking. Too much dopamine and they feel over-stimulated.
Chemistry of ‘walls’ and ‘flowers’
The introverted brain has a higher level of internal activity and thinking than the extroverted brain. It is dominated by the long, slow pathway of another neurotransmitter called acetylcholine. Introverts require a limited range of not too much or too little dopamine, another brain chemical, and a good level of acetylcholine to keep a calm feeling instituted. Acetylcholine serves as a trigger to the brain to conserve energy and stimulates good thinking and feeling.
Laney explains that the extroverted brain just doesn’t have as much internal activity going on. So, it scans the external world for stimulation to fuel the shorter, quicker dopamine pathway. “The signals from the brain travel to the Full-Throttle (sympathetic nervous) system that controls certain body functions and influences how ‘outies’ behave,” she says.
But, an extrovert needs its sidekick, adrenaline, to help cook up more dopamine in the brain, Laney says. Like plants to sunlight, their energy comes from the places they go; the people they see. “Leave an extrovert alone for two minutes and he will be calling someone on his cell phone.”
So, during these merry days, as extroverts chat away, hands and mouths dancing in a choreographed ballet, try to remember the lament of the introverted Rauch, “We can only dream that someday, when our condition is more widely understood, when perhaps an Introverts Rights movement has blossomed and borne fruit, it will not be impolite to say, ‘I’m an introvert. You are a wonderful person and I like you. But now please, shush.”
Of course, as with most studies, this is mostly speculation. Interesting, but it's not the Bible. Take it with a grain of salt. (Good luck picking a single grain up.)
