High-frequency changes in single-trial visual evoked potentials for unattended stimuli in chronic schizophrenia.

BACKGROUND: Patients with schizophrenia reveal changes in information processing associated with external stimuli, which is reflected in the measurements of brain evoked potentials. We discuss actual knowledge on electro- (EEG) and magnetoencephalographic (MEG) changes in schizophrenia. NEW METHOD: The commonly used averaging technique entails the loss of information regarding the generation of evoked responses. We propose a methodology to describe single-trial (non-averaged) visual evoked potentials (VEP) using spectral and statistical analyses. We analysed EEG data registered in the O1-Cz and O2-Cz leads during unattended pattern-reversal stimulation, collected from a group of adult patients with chronic schizophrenia, and compared them to those of healthy individuals. Short-time single-trial VEP were transformed to the frequency domain using the FFT algorithm. Changes of the spectral power were visualized using spectrograms which were created by stacking single-trial spectra across all trials. Measures of the absolute and the relative spectral power were calculated and compared statistically. RESULTS: In schizophrenia, the energy density of VEP oscillations is shifted towards higher (gamma) frequencies, compared to healthy individuals. These differences are statistically significant in all analysed frequency bands for the relative power. This indicates distorted early processing of visual stimuli in schizophrenia. COMPARISON WITH EXISTING METHODS: The main advantage of the presented methodology is its simplicity and ease of interpretation of obtained results. The presented observations complement the knowledge on gamma oscillations acquired from computationally more complex methods of time-frequency analysis. CONCLUSIONS: High-frequency changes for single-trial VEPs are detected in chronic schizophrenia.

[Distribution of latencies of visual evoked potentials in a sample of schizophrenic patients]. / Rozklad latencji zalamków wzrokowych potencjalów wywolanych w grupie pacjentów z rozpoznaniem schizofrenii.

AIM: The aim of the study is an analysis of distribution of visual evoked potentials (VEP) latencies in the group of schizophrenic and healthy subjects. METHOD: A study was carried out on a group of 30 patients (8 males and 22 females) with a DSM-III-R diagnosis of schizophrenia (disorganised schizophrenia--5, paranoid schizophrenia--12, residual schizophrenia--6, and undifferentiated schizophrenia--6). During the study 20 patients were given neuroleptics, 10 patients did not receive treatment. A control consisted of 50 healthy persons (25 males and 25 females). A stimulation of a chessboard pattern reversal (0.5 Hz, 30', 50 cd/m2) was applied. Evoked potentials were measured between top of a head (Cz) and occipital leads O1 and O2. RESULTS: Schizophrenic patients have frequently prolonged N2 latency, and shortened P300 latency. Three groups of patients have been distinguished, based on a pattern of latencies: (1) patients with prolonged latencies of all the waves (half of the patients), (2) patients with prolonged N2 latency, and shortened P300 latency (one fourth of the patients), and (3) patients with latencies similar to control (one fourth of the patients).