Like other scientists, he hoped to find a neurological cure to addiction, some mechanism for blocking that dopamine activity in the brain so that people wouldn’t succumb to the otherwise irresistible craving for cocaine, heroin and other powerfully addictive drugs.

But then, when he began studying addicts, he saw that drugs weren’t so irresistible after all.

“Eighty to 90 percent of people who use crack and methamphetamine don’t get addicted,” said Dr. Hart, an associate professor of psychology. “And the small number who do become addicted are nothing like the popular caricatures.”…

“If you’re living in a poor neighborhood deprived of options, there’s a certain rationality to keep taking a drug that will give you some temporary pleasure,” Dr. Hart said in an interview, arguing that the caricature of enslaved crack addicts comes from a misinterpretation of the famous rat experiments.