For instance, extroverts--people stereotypically depicted as the life of the party--appear to have more going on in a part of the brain called the medial orbitofrontal cortex, compared with introverts.
This was just one of the big five personality types that researchers attempted to link to specific brain regions. They found distinct brain activity related to four of those five personality types: introversion/extroversion, neuroticism, agreeableness, and conscientiousness. The only personality trait that couldn't be linked to specific brain activity was openness and intellect, which has been tied directly to intelligence.
It's interesting research. There are certain personality characteristics that I've had my whole life. While environment indisputably shapes our personalities, I wouldn't be surprised to learn that my brain came prepackaged with an inclination toward some of these traits, particularly my self-consciousness in social situations.
The real question, I suppose, is how plastic the brain may be. In other words, can we change our personalities, and if so, how much? Anyone who can definitely prove that they have the answer to that question will get a best-selling book, an appearance on Oprah, and several million dollars.