Diazepam blocks fear-potentiated startle in humans

The effects of an anxiolytic drug (diazepam) on emotional responses to aversive stimuli were investigated using physiological measures, including the startle probe reflex. Participants were 54 university students assigned to either a placebo group or a 10 mg or 15 mg diazepam group in a double-blind design. Blink responses to intermittent noise probes were recorded during viewing of neutral and unpleasant slides. Consistent with prior animal work, diazepam blocked startle potentiation during aversive stimulus processing without decreasing the overall magnitude of startle responses. These findings suggest that a common defensive state mediates startle reflex potentiation in animals and humans and that this index of fear can be used to assess the emotional effects of different drugs.