Deficits in sensorimotor gating as assessed by prepulse inhibition (PPI) of the startle reflex have been reported in schizophrenia. However, the state or trait nature of these deficits and the relationships with clinical features and psychopathological symptoms are not clear. To explore these issues, we performed a longitudinal study with schizophrenia inpatients. We examined 36 medicated schizophrenia inpatients twice in the course of an acute psychotic episode: recently after admission and after psychopathological improvement 2-3 weeks later. In addition, we examined 18 healthy control subjects twice (two weeks apart). Relative to control subjects, patients with schizophrenia had lower PPI only in the acute, but not in the improved clinical state. Larger PPI deficits were associated with more severe formal thought disorder and bizarre behavior. In the present longitudinal study, PPI deficits in schizophrenic patients appeared to be state dependent. Taking into account recent evidence from the literature we propose that reduced PPI may be a mediating vulnerability marker of schizophrenia: Impairments in sensorimotor mechanisms which subserve PPI of the startle reflex may both predispose individuals to develop psychosis, and, in addition, may covary with the presence of acute positive symptoms.

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Recent evidence suggests that electromyographic activity in the orbicularis oculi muscle occurring in response to sudden acoustic stimuli consists of two overlapping components: the blink and the startle reflex. The aim of the present study was to identify these two components in acoustically elicited eyeblink responses and to analyze their differential modulation by weak acoustic prepulses. The prevalence, latency and amplitude characteristics of double EMG peaks in pulse-alone and prepulse-pulse trials (PP) with 30 ms and 100 ms interstimulus intervals were assessed in 16 healthy volunteers.EMG responses with two peaks were registered in 42.6 % of the pulse-alone trials and in 56.2 % of the PP30 and 48.7 % of the PP100 trials, respectively. Prepulse inhibition of the amplitude was greater for the second peak (14.2 % (P2) vs. -11.5 % (P1) in PP30 trials; 62.6 % (P2) vs. 32.3 % (P1) in PP100 trials), resulting also in higher P1/P2 amplitude ratios in prepulse-pulse trials (P1/P2: 62.9 % in pulse-alone, 92.6 % in PP30 and 100.1 % in PP100 trials). In conclusion, double peaks are a common phenomenon in human studies of acoustically elicited blink responses. It is postulated that the first peak represents the auditory blink reflex, whereas the second peak corresponds to the startle reflex, which may be more susceptible to prepulse inhibition. This complexity should be taken into account in clinical studies of the modulation of the startle reflex.

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