BETHESDA, Md. (AP) — Lying inside a scanner, the patient watched as pictures appeared one by one: A bicycle. A cupcake. Heroin. Outside, researchers tracked her brain's reactions to the surprise sight of the drug she'd fought to kick.

Government scientists are starting to peek into the brains of people caught in the nation's opioid epidemic, to see if medicines proven to treat addiction, like methadone, do more than ease the cravings and withdrawal. Do they also heal a brain damaged by addiction? And which one works best for which patient?

They're fundamental questions considering that far too...