introvertism and brain activity

Given my bipolaristic proclivities, I relate totally to what is posted at spectratrix:

Introverts’ brains are much busier and therefore we need
little input from the environment to be at a comfortable brain
activation. Extroverts need a lot, and so there you will find people
who jump out of planes, rollercoast, and the like.

I had never heard this idea before, but it made intuitive sense to
me when I read it. I often feel like my brain is going a million miles
a minute, and to take in even more information can be quite difficult
at times. It seems to explain the overwhelmed feeling I sometimes get
in stressful situations; my brain is too busy processing my own stuff
to be able to deal with what’s going on around me.