In a famous scene in the first Matrix movie, a character takes a bite out of a juicy steak. He knows it's not real, but enjoys it anyway. In some ways, a video game -- just moving pixels on the screen -- is a similar virtual reality experience. No, the aliens in Halo 3 are not real, but we pretend they are. That is how a game can pull you from a living-room couch into a foreign realm.

Energy drinks like Monster, Full Throttle, Red Bull and others account for more than $3 billion in annual sales in the U.S., and roughly one-third of people between the ages of twelve and 24 say they suck them down on a regular basis. The beverages have been linked to a number of negative health effects, but now an addiction researcher at the University of Buffalo has published a report demonstrating that excessive consumption is also correlated to risky behavior such as unprotected sex, substance abuse and violence.

Most of us have friends who are social smokers. They're the ones who don't ever take work breaks under the overhang with the smoking crowd, but come Friday, they're outside the bar having a butt or two as the night wears on. They rarely buy cigarettes because they don't want a whole pack; they're more likely to ask for a smoke from a friend. They never seem to get hooked and can go for weeks without even thinking about it. How do they do it when so many of the rest of us are hopelessly addicted?

Jeff was your everyday successful guy. He owned a thriving clothing business, had plenty of friends, and seemed to be living the sweet life in sunny Florida. Except for one thing: He was a heroin addict. It began eight years ago at a party with a snort of just one line of the drug. Within weeks, Jeff, then 30, was a frequent user and enjoying it. So much so that before long snorting didn't deliver a powerful enough high to satisfy his cravings; he moved on to smoking heroin.

It's Martin Luther King Jr.'s birthday, and Hans Breiter, director of the Motivation and Emotion Neuroscience Center at Massachusetts General Hospital, has the day off. Sort of. He's sitting in his home art studio, gluing together a statue that broke soon after his 9-year-old son made it. Meanwhile, with his cellphone kinked against his neck, Breiter is fielding call after call, discussing the intricacies of neuroscience with people he couldn't squeeze into his hectic weekday schedule.