From: http://www.creators.com/advice/advice-goddess-amy-alkon/the-larva-of-the-party.html
Ever since Freud decided (sans evidence) that introverts were repressed, narcissistic trolls under the bridge, extraversion has been considered the ideal and introverts have been seen as socially stunted. Introversion is also wrongly conflated with shyness, but shyness is fear- and shame-based — quite different from seeing no reason to say anything to strangers unless you or they are on fire.
More and more, research points to a strong biological basis for personality. Brain imaging shows distinct differences in introverts and extraverts. Studies by neuroscientist Debra L. Johnson and others found that extraverts, who get energized from external stimulation like meeting new people, have increased blood flow to rear areas of the brain for sensory processing (like listening, touching, watching). Introverts, who tend to be more pensive and introspective, and are easily overwhelmed by too much external stimulation, showed more blood flow altogether (indicating more internal stimulation), over more complicated pathways, with more activity in frontal regions for inward tasks like problem-solving, reasoning, and remembering.
Put that together with a Chinese study adding evidence that introverts get socked with a higher level of cortical arousal from stimuli, and you get the idea that urging introverts to be more outgoing is a bit like urging scissors to be more like a stapler.
The funny part is, I have no problem understanding the differences between introversion and extroversion, but most of the extroverts I know are just utterly baffled by introversion even when I show them stuff like this. Which is why my catch phrase is: You don’t have to understand, you just have to accept.