It is hypothesized that the event-related potentials are generated by different electrophysiological mechanisms, i.e., event-related power increase and enhanced degree of phase-locking over trial. The study aimed to characterize the relative contribution of these mechanisms to the ERP in patients with schizophrenia (SCZ).

One hundred and fifteen chronic stabilized SCZ and 62 healthy controls (HC) recruited to the study of the Italian Network for Research on Psychoses were included. Scalp potentials were recorded during a standard auditory oddball task. Stimulus-locked segments were extracted for all standard trials and correctly hit target trials. Trials contaminated by other artifacts were rejected. For each subject and stimulus type the event-related spectral perturbation (ERSP) and the inter-trial-coherence (ITC) were computed to assess event-related power increase and inter-trial phase-locking. The two groups were compared using Student's t-test followed by Bonferroni correction for multiple comparisons.

SCZ presented a reduced amplitude of both N100 and P3b. For both standard and target stimuli, at Cz and Pz, ERSP was reduced in SCZ in the delta-theta band (from 0 up to 400 ms). The ITC index, at the same channels, was reduced in SCZ in the delta band for standard stimuli (from 0 to 300 ms), and in both delta and theta bands for target stimuli (from 300 to 400 ms).

Our results indicate that alterations of both mechanisms are involved in N100 and P3b amplitude reduction observed in SCZ. Inter-trial phase-locking abnormalities for N100 were limited to the delta band, while for P3b involved delta and theta frequencies.

The authors have not supplied their declaration of competing interest.