Effects of Magnitude of Leading Stimulus on Prepulse Inhibition of Auditory Evoked Cerebral Responses: An Exploratory Study.

An abrupt change in a sound feature (test stimulus) elicits a specific cerebral response, which is attenuated by a weaker sound feature change (prepulse) preceding the test stimulus. As an exploratory study, we investigated whether and how the magnitude of the change of the prepulse affects the degree of prepulse inhibition (PPI). Sound stimuli were 650 ms trains of clicks at 100 Hz. The test stimulus was an abrupt sound pressure increase (by 10 dB) in the click train. Three consecutive clicks, weaker (-5 dB, -10 dB, -30 dB, or gap) than the baseline, at 30, 40, and 50 ms before the test stimulus, were used as prepulses. Magnetic responses to the ten types of stimuli (test stimulus alone, control, four types of tests with prepulses, and four types of prepulses alone) were recorded in 10 healthy subjects. The change-related N1m component, peaking at approximately 130 ms, and its PPI were investigated. The degree of PPI caused by the -5 dB prepulse was significantly weaker than that caused by other prepulses. The degree of PPI caused by further decreases in prepulse magnitude showed a plateau level between the -10 dB and gap prepulses. The results suggest that there is a physiologically significant range of sensory changes for PPI, which plays a role in the change detection for survival.