EFFECTS OF STRESS AND SHOCK ANTICIPATION ON PREPULSE INHIBITION OF THE STARTLE REFLEX

The effects of shock anticipation and attention to external stimuli on prepulse inhibition (PPI) were compared. In the threat-of-shock exper iment, acoustic startle stimuli were presented with and without prepul ses when aversive shocks were or were not anticipated. In the control experiment, startle and prepulse stimuli were delivered during periods with attended or ignored external stimuli. In the threat-of-shock exp eriment, startle was potentiated (fear-potentiated startle) and PPI wa s increased by shock anticipation. A gradual reduction in the overall PPI throughout the experiment was also found. In the control experimen t, only PPI was increased in the attend condition. The PPI level remai ned constant throughout the experiment. The increase in PPI in the thr eat and attend conditions may have resulted from an increase in the ge neral level of alertness that facilitated the processing of the prepul se. The gradual decrease in PPI in the threat experiment was hypothesi zed to result from a progressive deficit in sensory functioning due to the stressful nature of repeated shock anticipation.