Why do you choose Coke over Pepsi, Corona over Bud, Crest over Colgate? You don’t think much about these choices, you say; your gut decides. Marketing guru Martin Lindstrom says otherwise. Your preference for Macs over PCs is embedded in your brain circuitry. In “Buyology,” he shares the results of a three-year, $7 million study, in which he submitted 2,000 people to fMRI scans to explore what, exactly, happens in your brain to make you stand in line all night for an iPhone.