The study placed rats inside of the maze (don't all studies do that?), and trained them to associate one side of the maze with either cookies or cocaine, and the other with rice cakes. The students soon found that the rats had "an equally strong association between the pleasure effects of eating Oreos" as they had when they could choose cocaine over rice cakes, essentially proving that the rats were equally motivated by both options (and, like people, not too excited about rice cakes).
It's still unclear whether the correlative aspects of the study have informed the results (namely whether the rats were responding less to a love of cocaine and Oreos as much as they were a distaste to rice cakes), but the concept of the processed food industry providing a snack with the same addictive quality as a hard drug is simultaneously shocking and, to many, expected.
The most curious revelation? One researcher told Grist.org, that the rats, too, would split the Oreo in half and eat the middle first. So there's something to chew on for a while.