On the feasibility to detect and to quantify prepulse-elicited reaction in prepulse inhibition of the acoustic startle reflex in humans

The possibility that the prepulse stimulus typically employed in the studies of prepulse inhibition (PPI) can produce observable response has been questioned recently. Conflicting reports range from observations of prepulse-elicited startle reaction to a complete lack of detectable prepulse-elicited reactions in healthy volunteers. This controversy is subjected to critical examination in the present study. The ability of prepulse stimuli to induce PPI and to elicit measurable responses was examined in two separate experiments using prepulses ranging from 6 to 18 dB above background (experiment 1), or 1 to 5 dB above background (experiment 2). Three levels of pulse stimulus were employed: 95, 105 and 115 dBA. Clear PPI and prepulse-elicited reaction were obtained in experiment 1, while neither effect was evident in experiment 2. Non-startle-eliciting prepulses that are of sufficient intensities to induce reliable PPI are associated with detectable and quantifiable response, confirming that direct evaluation of prepulse-processing is feasible and practical. This provides an additional measure of theoretical and potentially clinical relevance to PPI, and it ought to be included in future studies in patients as well as healthy subjects.