Jonah Lehrer analyzes studies about the differences between Coke, Mexican Coke, and Pepsi:
When [Coke and Pepsi] were offered unlabeled, the dopamine reward pathway became active. This makes sense: the pathway helps process appetitive rewards, like sugary drinks, which provide us with a rush of sweet pleasure. However, when the subjects drank a cola with a Coke label, an additional set of brain areas became extremely active. The DLPFC, hippocampus and our midbrain emotional areas reacted strongly to the red cursive of Coke, but not to the blue Pepsi logo. (This happened even when subjects were given Pepsi with a Coke label.) ... The end result is a strong preference for Coke, even though it tastes identical to Pepsi. ...
Mexican Coke has become my Coke.
I see that glass bottle and I’m flooded with all sorts of dopaminergic associations, those smug feelings reminding me that I don’t drink that generic high-fructose corn syrup crap. I drink the real stuff, the cola made with old-fashioned sugar. But those associations are almost certainly an illusion my tongue is too crude a sensory device to parse the difference between Coke and Pepsi, let alone between slightly different formulations of the exact same drink.