The goal of this protocol is to use a targeted serotonergic manipulation (tryptophan depletion) and specific neurocognitive and neuroimaging paradigms to consider the role of serotonin in emotional processing. In particular, we will evaluate claims that serotonin has a role in the effective processing of aversive signals. In addition, we will examine whether tryptophan depletion will attenuate the neural response to aversive material.