There have been many studies to prove that introversion is an actual phenomenon of the brain. Here is an article I found that sums it up pretty good.
"The introverted brain
Introverts’ brains work differently than extroverts’. For one thing, introverts have more blood flow to their brains than extroverts. According to Marti Olsen Laney, that indicates more internal stimulation and sensitivity. The blood in an introvert’s brain travels longer, more complicated pathways and focuses on parts of the brain involved with internal experiences like remembering, solving problems and planning.
Introverts’ brains still use dopamine but are more sensitive to it and too much of it will cause over-stimulation. The more dominant neurotransmitter found in the introvert’s neuro-pathways is acetylcholine. Acetylcholine affects attention and learning, influences the ability to stay calm and alert, utilizes long-term memory and activates voluntary movement. Not surprisingly, acetylcholine stimulates a good feeling when we think and feel.
Acetylcholine acts as an inhibitory neurotransmitter when it activates our parasympathetic nervous system, which helps us calm down and conserve energy when stimulated. The sympathetic nervous system (fight or flight) has the opposite effect. It is characterized by activity and mobility and employed more by the extroverted brain."
A lot of people that don't understand introversion think it's just a personality thing and it's because introverts don't want to or haven't "broken out their shell". Telling an introvert that they need to "change" or be "fixed" an introvert will probably leave them very upset and irritated. The best thing that can be done is to understand them, simply because this is an actual chemical and physiological design of our brain.