Prepulse inhibition (PPI) of auditory startle reflex is associated with PPI of auditory-evoked theta oscillations in healthy humans

The aim of the current study was to investigate the auditory-evoked theta oscillatory activity associated with prepulse inhibition (PPI) of the startle reflex in healthy humans. Concurrent electroencephalogram (EEG) and auditory startle reflex were recorded from 19 healthy controls during Pulse-Alone and Prepulse + Pulse trials with 60, 120, and 240 ms prepulse–pulse intervals. Compared to Pulse-Alone trials significant PPI of the startle reflex occurred on all Prepulse + Pulse trials and a significant startle latency reduction occurred on 60 and 120 ms Prepulse + Pulse trials. The largest evoked potentials to auditory stimuli occurred at fronto-central locations. PPI of theta oscillations occurred at frontal, central, and parietal locations. These results suggest that PPI functions not only as sensory-motor gating but also as sensory-cognitive gating since theta oscillations are involved in control of cognitive processes. Absence of significant correlations between PPI of the startle reflex and of theta oscillations at all electrode locations indicates that the two processes may be controlled by different neural mechanisms.