To understand the effect of anxiety-relieving drugs on fear and anxiety, researchers often have participants anticipate unpleasant stimuli. Anticipating unpleasant stimuli increases or potentiates a simple reflex called the startle reflex. The so-called fear-potentiated startle reflex (FPS) effect may be blocked or reduced by anxiety-relieving drugs. Evidence suggests that the FPS can be mediated by two mechanisms that regulate the phasic- and sustained enhancement of startle. This study will elicit phasic and sustained FPS in participants by having them anticipate moderately painful stimuli that are administered predictably and unpredictably. The main goal of this study is to assess the affect of alprazolam on the phasic and sustained enhancement of startle.