Measuring the time course of anticipatory anxiety using the fear-potentiated startle reflex.

The time course of the facilitation of the acoustic startle reflex induced by anticipation of electric shocks was measured in 20 normal volunteers. Shocks could be administered during the last 10 s of 45-s threat conditions but not during 50-s no-threat conditions, each condition being signaled by a different light. Consistent with previous data, overall eyeblink startle levels were higher during the threat than during the no-threat conditions. However, the magnitude of this fear-potentiated startle effect became progressively larger in the threat condition the longer the light was on and then abruptly decreased with the onset of the light signaling the no-threat condition. These effects of the threat of shock on startle were interpreted in terms of anticipatory anxiety. Other interpretations, such as changes in selective or generalized attention, were also discussed. This paradigm provides a method to assess the time course of anticipatory anxiety in humans.