All participants in the proposed study will also undergo a functional MRI with the Motivational Incentive Delay task (fMRI/MID). This task is thought to reflect dopaminergic transmission in the brain-reward system but is safer and more feasible than PET. The investigators hypothesize that fMRI/MID will correlate strongly with results from the PET procedure, thereby suggesting that it also reflects the status of striatal dopamine functioning. In addition, a group of healthy controls will undergo one fMRI scan in order to validate the procedure and to assess if a deficit can be detected in cocaine-dependent participants. Cocaine-dependent participants will undergo two fMRI/MID, one at baseline and another after a week of treatment with LCE to assess if treatment with LCE may reverse baseline deficits and if this change is associated with clinical improvement.