http://en.wikipedia.org/wiki/Social_defeat

Scroll down to "effect on humans". It's a very interesting read and should induce some healthy doubt about whether social extraversion has anything at all to do with socionics extraversion.

Other factors of interest to me are genetics as well, especially anxiety and overarousal. The way introverts distribute physical resources in the brain is also of interest to me, and possibly has relationships with anxiety and hypervigilance.