IED is a condition characterized by a failure to resist aggressive impulses. IED is a behavioral defined condition for which effective treatments have not been identified. Research suggests that serotonin (5-HT), a chemical that helps regulate mood and emotions, may play a role in the response to pharmacological IED treatments. This study will examine the relationship between 5-HT receptors and response to treatment with fluoxetine or divalproex. In addition, this study will examine people with IED and those without the condition to determine whether there are differences in their 5-HT receptor and transporter systems.