I heard at uni that
Extraverts are supposed to have a Less Excitable Frontal Cortex
Introverts are supposed to have a More Excitable Frontal Cortex.
Not sure exactly if that was the brain region but you get the idea. It does make sense to me as Extraverts have a less excitable cortex they need more stimulation to get going and vice versa. If i remember correctly they suggested that introverts wake up easier in the morning but slow down earlier at night. Im like a damn zombie in the morning and definately do take some warming up time. FDG says he wakes up early though so perhaps this doesn't make total sense.
FDG suggested that the more Extraverted someone is the easier they fall asleep. I suppose that would make some sense as when an Extravert is alone their frontal cortex should be at a lower level of arousal than the introvert. I know my ISTj dad wakes up at around 4:00am and thats his time. My time is 10:00pm-2:00am.
My INFj friend suggested alcohol could have an interesting affect on Introverts. Since alcohol is a depressant of brain activity it should actually calm down an Introverts brain and make them more outgoing and seek more stimulation. Society seems to value Extraversion so introverts probably feel very excited by feeling outgoing. On the other hand Alcohol should actually depress an extravert's cortex further, perhaps making them less extraverted.
I have definately witnessed a number of really shy and introverted people go Psycho on Alcohol. I used to know this insanely shy guy who would turn into a wild party dude when he got trashed. Generally i feel normal and simply un-inhibited with a little bit but with a little more i probably do go all quiet.
One problem of course with all of this is its a more basic perhaps MBTI view on Extraversion / Introversion and i think the functions would make every Extravert and Introvert very unique. Im just spewing stuff out there as food for thought.