Caroline Zink and her team at the National Institutes of Mental Health have produced a nifty study of which brain regions get active when our place in a status hierarchy is threatened.
The subjects were given a simple test (note when a circle changes color in a particular way). They then did the task against competitors. When the subjects' position against the competitors did not change, they focused on doing the task better to move up. When the subjects' position did change, sometimes falling below the competitors' positions, the subjects' emotional centers fired up, too. Fear of losing position seemed to generate anxiety, even in as trivial a hierarchy as this one.
What is more, the competitors were actually imaginary, and their rank relative to the subject was manipulated by the researchers.