Prepulse Inhibition of the Auditory Off-Response: A Magnetoencephalographic Study

A weak preceding sound stimulus attenuates the startle response evoked by an intense sound stimulus. Like startle reflexes, change-related auditory responses are suppressed by a weak leading stimulus (ie, a prepulse). We aim to examine whether a prepulse inhibits cerebral responses to the sound offset and how the prepulse magnitude affects the degree of the prepulse inhibition (PPI). Using magnetoencephalography, we recorded the Off-P50m elicited by an offset of a train sound of 100-Hz clicks in 12 healthy subjects. A single click slightly louder (+1.5, +3, or +5 dB) than the background sound of 80 dB was inserted 50 ms before the sound offset as a prepulse. We performed a dipole source analysis of the Off-P50m, and we measured its latency and amplitude using the source strength waveforms. The origin of the Off-P50m was estimated to be the auditory cortex on both hemispheres. The Off-P50m was clearly attenuated by the prepulses, and the degree of PPI was greater with a louder prepulse. The Off-P50m is considered to be a simple change-related response, which does not overlap with a processing of incoming sounds. Thus, the Off-P50m and its PPI comprise a valuable tool for investigating the neural inhibitory system.