An analysis of the brainʹs transfer properties in schizophrenia: Amplitude frequency characteristics and evoked potentials during sleep

Background: Classical analysis of spontaneous sleep electroencephalogram (EEG) in schizophrenia commonly reveals alterations of sleep continuity, number of awakenings, slow-wave sleep (SWS), and REM sleep compared to healthy controls; however, conventional analysis cannot help understand dynamic differences of the sleep EEG during different sleep stages. Methods: We measured late components of auditory evoked potentials (AEPs) and visual evoked potentials (VEPs) during different sleep stages of 11 schizophrenic inpatients and in a sex- and age-matched control group from scalp positions FZ, CZ, and PZ. According to linear system theory, we then computed the amplitude-frequency characteristic (AFC) from averaged AEPs and VEPs in different sleep stages. These AFCs describe the input-output relation of the system under study, leading to a characterization of the transfer properties of the schizophrenic brain during sleep. Results: Significant differences could be found for the transfer properties during stage II and SWS between schizophrenics and controls. During REM a marked enhancement of theta resonance was seen in schizophrenics. Conclusions: The results of the present study point to highly different central nervous system transfer properties in schizophrenics and controls. Compared to previous investigations in depression, the results provide additional information for distinguishing schizophrenia and depression in EEG studies.