Extroversion, Introversion -- a closer examination
This is what we currently have to show the differentiation. Examples omitted are studies and theories based on self-perception and hypothesis:
Joy and Fear, how ambiversion divides on an MRI: http://www.gluecksforschung.de/Hirnf...-Gesichter.pdf
Regarding introversion and extroversion in genetics: "Twin studies find a genetic component of 39% to 58%. In terms of the environmental component, the shared family environment appears to be far less important than individual environmental factors that are not shared between siblings." Source: Journal of Personality and Social Psychology Vol. 54, no. 6. 1031–1039.
This study's abstract is as follows: "We administered the Multidimensional Personality Questionnaire (MPQ) to 217 monozygotic and 114 dizygotic reared-together adult twin pairs and 44 monozygotic reared-apart adult twin pairs. A four-parameter biometric model (incorporating genetic, additive versus nonadditive, shared family-environment, and unshared environment components) and five reduced models were fitted through maximum-likelihood techniques to data obtained with the 11 primary MPQ scales and its 3 higher order scales. Solely environmental models did not fit any of the scales. Although the other reduced models, including the simple additive model, did fit many of the scales, only the full model provided a satisfactory fit for all scales. Heritabilities estimated by the full model ranged from .39 to .58. Consistent with previous reports, but contrary to widely held beliefs, the overall contribution of a common family-environment component was small and negligible for all but 2 of the 14 personality measures. Evidence of significant nonadditive genetic effects, possibly emergenic (epistatic) in nature, was obtained for 3 of the measures. (PsycINFO Database Record (c) 2012 APA, all rights reserved)"
In regard to the biochemicals of an extrovert, "Extraversion has been linked to higher sensitivity of the mesolimbic dopamine system to potentially rewarding stimuli." Source: Behavioral and Brain Sciences, 22, 491–517.
Dopamine relates to the following in regard to activity and reward-seeking biolology: Dopamine has many functions in the brain, including important roles in behavior and cognition, voluntary movement, motivation, punishment and reward, inhibition of prolactin production (involved in lactation and sexual gratification), sleep, mood, attention, working memory, and learning.
In regard to surgency, the emotional reactivity in which a person tends towards high levels of positive affect, "Extraversion has also been linked to physiological factors such as respiration, through its association with surgency.: Source: Journal of Child Psychology and Psychiatry 44 (1): 2–32.
In regard to psychology, introversion is defined as, "Introversion is "the state of or tendency toward being wholly or predominantly concerned with and interested in one's own mental life". Extroversion is defined as, "Extraversion is "the act, state, or habit of being predominantly concerned with and obtaining gratification from what is outside the self". -Merriam Webster Dictionary
Note: Still Editting this post.