0
At the same time, other research shows that there's something to the reward theory of E/I. In a study published earlier this year, researchers gave participants Ritalin, a drug that stimulates the release of the chemical dopamine, which is involved in reward and motivation. While on Ritalin, the participants watched videos showing random nature scenes. After three days, the scientists took away the drug, and then had the participants watch videos in the lab again — the extroverts were excited by the videos, while the introverts were not. LiveScience explains:
The results suggest that Ritalin's effects on the dopamine system didn't translate into reward or motivation for the introverts. That suggests that introverts have a fundamental difference in how strongly they process rewards from their environment, with the brains of introverts weighing internal cues more strongly than external motivational and reward cues, the researchers write in the paper.
Studies have also suggested that the brains of extroverts pay more attention to human faces than the brains of introverts. In fact, researchers have found that the brains of introverts respond to faces in a similar way that they respond to images of flowers, whereas the extroverts' brains show a stronger response to faces — this suggests that human faces, or people in general, hold more significance to extroverts (which, perhaps, partially explains why they seek out other people's company).