Abnormal auditory information processing in schizophrenia revealed by nonstationary signal analysis

Two of the most consistently reported evoked potential abnormalities in schizophrenia are a decreased amplitude of the mid-latency evoked responses and decreased sensory gating capability. The cause of these abnormalities is largely unknown. In the present study, we investigate to what degree these abnormalities may be explained in terms of EEG synchronization deficits. The auditory EPs from 20 normal subjects and 19 schizophrenia patients were obtained using a double click paradigm, in which two identical stimuli were delivered with an inter-stimulus interval of 500 ms and an inter-pair interval of 8 s. The Piecewise Prony Method (PPM) was used to decompose single trial auditory evoked potentials into sinusoidal, exponentially decaying/increasing components. Pre-and post-stimulus phase histograms were compared to determine the degree of phase synchronization produced by auditory stimulation in the two populations. It was found that schizophrenia patients have a phase synchronization deficiency, as compared to a normal control group, especially in the 4 Hz through 12 Hz frequency range. This deficiency explains the lower EP amplitudes and reduced sensory gating reported in schizophrenic subjects.