There has been a surge in technologies to observe how genes and proteins change in the brain during disease. Yet, it has remained difficult to distinguish cause from effect; whether a given protein change in a specific cell type is the cause of behavioral impairments, a compensatory phenomenon, or simply an epiphenomenon. I will describe a new method, DART (drugs acutely restricted by tethering), to rapidly restrict drugs to genetically defined neurons in behaving mice. The approach offers a new way to establish causal circuit and molecular substrates of normal and aberrant behavior.