The human prefrontal cortex may not be special in terms of its size relative to other primates, but it is still a pretty special.

Want to know what it does?  Here’s a start:
Miller, E.K. and Cohen, J.D. (2001) An integrative theory of prefrontal cortex function. Annual Review of Neuroscience, 24:167-202.  Designated a Current Classic by Thomson Scientific as among the most cited papers in Neuroscience and Behavior. View PDF »