A drug being studied as a fast-acting mood-lifter restored pleasure-seeking behavior independent of -- and ahead of -- its other antidepressant effects. Within 40 minutes after a single infusion of ketamine, treatment-resistant depressed bipolar disorder patients experienced a reversal of a key symptom -- loss of interest in pleasurable activities -- which lasted up to 14 days. Brain scans traced the agent's action to boosted activity in areas at the front and deep in the right hemisphere of the brain.