Why Did Harry's Scar Hurt?

Question

J.K. Rowling wrote fairly extensively about Harry's scar hurting when Voldemort was feeling certain emotions or when there was a mind connection between Harry and Voldemort. Why, though, did Harry experience pain in his scar, rather than throughout his body as a whole? What was the significance of the pain Harry felt in his scar? If it weren't important, I don't think it would've been such a theme throughout the books; however, none of the books address why Harry has pain in his scar or what the significance of the pain is.

ETA: Please no HP Wikia answers.

Answer 1

According to the LeakyCauldron, you should listen to:PotterCast 130.

J. K. Rowling stated that the pain from Harry's scar on his forehead is caused by the piece of Voldemort's soul trying to leave his body through the wound it entered to rejoin its master's soul

Answer 2

Why does Harry feel pain in his scar?

J.K. Rowling: Well, of course the pain he feels [in his scar] whenever Voldemort's particularly active is this piece of soul seeking to rejoin the master soul. When his scar is hurting him so much, that's not scar tissue hurting him. That's this piece of soul really wanting to get back out the way it entered. It really wants to- it entered this boy's body through a wound, and it wants to rejoin the master. So when Voldemort's near him, when he's particularly active, this connection, (JN: Oh, my gosh!) it was always there. That's what I always imagined this pain was. Yes, so there you go.

_{J.K. Rowling - [THE LEAKY CAULDRON - POTTERCAST'S INTERVIEW WITH J.K. ROWLING] - 12.23.2007}