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Magnetic motor conduction parameters are unaltered in schizophrenia, but transcallosal inhibition is significantly delayed and prolonged. This may indicate abnormal function of the corpus callosum in these patients.

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.

There is increasing evidence for an influence of directed attention on prepulse inhibition (PPI) of the acoustic startle reflex. However, the existing paradigms for the assessment of this effect have methodological problems and pitfalls. In particular, most previous studies used a paradigm which directed the attention of subjects to the prepulse only. In the present study, we used a modified paradigm which directed the attention of the subjects both to the prepulse and the pulse. Twenty healthy male subjects were instructed trial by trial either to relax or to attend to the startle stimulus and decide whether it was a ‘simple’ (prepulse alone or pulse alone) or a ‘composite’ trial (pulse plus a prepulse or postpulse). Directed attention enhanced PPI at the lead interval of 240 ms, but not at the lead interval of 100 ms. This finding is in line with the idea that attention contributes to PPI when there is enough time for the attentional mechanisms to exert an influence. This new paradigm offers a valuable tool for the study of attentional modulation of sensorimotor gating in humans.

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