Repeated testing of prepulse inhibition and habituation of the startle reflex: a study in healthy human controls

The aim of this study was to examine the effect of repeated testing on prep ulse inhibition (PPI) and habituation of the startle reflex. Fifteen health y control subjects (eight males, mean age 30 years; seven females, mean age 29 years) were tested on three occasions across the same day separated by a minimum of 2 h. An acoustic probe of 40-msec bursts of 116dB(A) white noi se over a continuous background noise of 70dB(A) was presented binaurally t hrough headphones and the eye-blink component of the startle response was m easured taking electromyographic recordings from the right orbicularis ocul i. The test session was identical at each time point and consisted of two b locks of 12 randomly mixed trials of four pulse-alone, four 60-msec prepuls e and four 120-msec prepulse trials enclosed by two blocks each of six puls e-alone trials. There was huge variation in individual response magnitude t hat was independent of subsequent PPI in both women and men. Women showed g reater PPI in the second half of sessions with the 120-msec prepulse only; but PPI was not altered significantly in either group between sessions acro ss the day. In general, there was good test-retest reliability of PPI espec ially within trial type. Normal reflex habituation occurred across sessions and this effect was preserved in sessions across the day. Latency of respo nse was significantly reduced in a session by the 60-msec trial type compar ed to the 120-msec trial type, as previously reported. Our results suggest that measures of PPI and habituation of the startle response are appropriat e and reliable for a within-subject, test-retest design.