New work in Nature Neuroscience offers some promise for understanding cocaine addiction. Researchers genetically engineered mice to produce cadherin, a protein involved in learning that helps strengthen the brain’s neural connections. The mice cranked out this protein in their reward circuits, a brain area that drives us to seek pleasure-inducing experiences and a key component in addiction. After introducing the cadherin-laden mice to cocaine multiple times, experts expected the rodents to crave the drug. Instead, the critters carried on without interest: The excess protein actually clogged their reward center circuitry, preventing the mice from getting hooked. The results point to the importance of biochemistry in addiction.