No, your child hasn't been taken over by an alien.  Beneath the bright pink hair and new piercings is the same baby you held not so long ago.  Why the transformation?  What can teens be thinking?  It turns out that teen brains aren't just adult brains in miniature  - they physically have more growing up to do.  This report from NPR's morning edition explains how an exasperated mom (who's also a neuroscientist) made the connection.