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We examined whether correlations previously found between symptoms of schizophrenia patients and the amplitude of an event-related potential (ERP), the N400, could be also found between schizotypal experiences of healthy subjects and the N400. We chose a semantic categorization task previously used with patients. Schizotypal experiences were measured with the schizotypal personality questionnaire (SPQ). The effects of the other factors were controlled for when assessing the correlations between each SPQ factor and N400s. These correlations were assessed at each electrode site to see whether their distribution on the scalp follows that of the N400 effect. Disorganization and interpersonal scores were found to correlate with ERPs in the N400 time window, as previously reported for the comparable symptoms of patients. However, the scalp distribution of these correlations differed from that of the N400 effect.

A previous study suggests that the amplitude of the N400 event-related potentials (ERPs) of healthy subjects does not vary with their delusional-like ideations. This contrasts with the smaller N400 amplitudes observed in more- than in less-deluded schizophrenia patients. Here, we hypothesize that these smaller N400 amplitudes were related to the paranoid feelings patients had during the ERP recording. We thus induced this type of feelings in healthy subjects. Delusional-like ideation was assessed with the schizotypal personality questionnaire. Thirty-four healthy subjects completed a semantic categorization task. Paranoid feelings were significantly enhanced by the induction. In these conditions, greater delusional-like ideation scores were associated with smaller N400 amplitudes and larger late positive components. Controlling for the two other schizotypal factors strengthened these results. These findings may help us understand why delusions persist.

Emotional distress and reasoning biases are two factors known to contribute to delusions. As a step towards elucidating mechanisms underlying delusions, the main aim of this study was to evaluate a possible "jumping to new conclusions" reasoning bias in healthy people with delusional ideation and its association with emotions. We surveyed 80 healthy participants, measuring levels of depression, anxiety, cognitive error and delusional ideation. Participants completed two versions of the beads task to evaluate their reasoning style. Results showed that people with delusional ideation reached a conclusion after less information, as expected. Interestingly, they also tended to change their conclusions more often than people without delusional ideation and did so with greater conviction. Depression and cognitive errors were strong predictors of delusional ideation but not of reasoning style. We conclude that delusional ideation in non-psychotic individuals is independently predicted by depressive symptoms and by a high conviction in new conclusions.

The amplitude of the P300 event-related potential (ERP) has been reported to be reduced over left compared to right temporal sites in schizophrenia patients. This left temporal P300 reduction has been associated with positive symptom severity and gray matter reduction in the left superior temporal gyrus. We investigated a group of patients with a first episode of schizophrenia spectrum psychosis and a group of normal controls to verify if P300 amplitude asymmetry already exists around the time of presentation for treatment. Relative to normal control subjects, no P300 asymmetry was found in patients. Nevertheless, P300 asymmetry was correlated with the severity of positive symptoms and worse global functioning (GAF), a good predictor of poor outcome.

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