Columbia professor Carl Hart has spent a lot of time studying people who are seemingly addicted to crack or meth. And his findings might surprise you. Often, when given the choice between taking more of the drug or getting some other reward (such as the promise of a small cash payment), the drug “addicts” choose the latter. Hart explains: “The key factor is the environment, whether you’re talking about humans or rat. The rats that keep pressing the lever for cocaine are the ones who are stressed out because they’ve been raised in solitary conditions and have no other options. But when you enrich their environment, and give them access to sweets and let them play with other rats, they stop pressing the lever.” Interesting stuff from the NYT: The Rational Choices of Crack Addicts.