The dependence of P300 amplitude on gamma synchrony breaks down in schizophrenia

Introduction: Auditory P300 amplitude reduction in schizophrenia is canonical and may be explained by poor synchronization or reduced power of the underlying neural activity. We asked if patients have reduced synchrony and power, and whether together with P300 amplitude, they make unique or overlapping contributions to the discrimination between patients and controls. We also asked whether people who have large P300s have higher power and greater synchrony of neural activity, and if the relationships between P300 and power and synchrony are different in patients and healthy controls. Methods: We recorded EEG data from 22 controls and 21 patients with schizophrenia (DSM-IV) while they performed an auditory target detection task. We used wavelet analyses of the single trial data to estimate total power and synchrony of delta, theta, alpha, beta, and gamma activity in a 50ms window around the peak of the P300 to the target. We measured P300 amplitude from the average of the single trials, in a 50ms window around its peak. Results and conclusions: P300 amplitude and delta and theta synchrony were reduced in patients; delta power and synchrony better distinguished between groups than P300 amplitude. In healthy controls, but not patients, gamma synchrony predicted P300 amplitude. In patients, P300 and gamma synchrony are affected by independent factors; the relationship between them is attenuated by an additional pathophysiological process.