Oszillatorische Gehirnaktivität von Patienten mit schizophrenen Störungen und Gesunden bei multistabiler Wahrnehmung

Objective: Patients with schizophrenia seem to be impaired in binding single visual stimuli-features into coherent objects. For this process, interaction of top-down and bottom-up processing has to be intact. Neural oscillations seem to be a fundamental mechanism for coordinated communication of neural circuits. They have been proposed to reflect the spatio-temporal integration of sensory and cognitive information for creating coherent perception. Method: An EEG examination of schizophrenia patients as well as healthy control subjects was performed during the processing of an apparent motion stimulus, a stroboscopic effect, which induces two possible endogenously generated perceptions. Furthermore, a modified control stimulus was presented with exogenous reversals of the stimulus. Event-related oscillations resp. event-related spectral perturbation (ERSP) of delta (0-4 Hz), theta (3-8 Hz), alpha (8-13 Hz), beta (14-28 Hz) and gamma oscillations (28-48 Hz) were analyzed. Results: The reaction time of patients in the control conditions is significantly slower. They show anslightly reduced delta power for both conditions, their theta-activity was significantly less increased than in the control group. Moreover, patients had a stronger decrease of alpha activity during the reversal activity over posterior electrodes. Both groups show this decrease in the beta frequency. In ambiguous perception, there are topographical differences between the groups. Patients show a shift from posterior to central regions in the gamma response. Conclusion: The results indicate a functional involvement of all five frequencies in multistable perception. Patients with schizophrenia seem to suffer from an impaired top-down influence of delta and theta in perceptual organisation of ambiguous patterns. With respect to the weaker performance in reaction time, it seems as if there is a reduced impact of top-down organisation, while generating the coherent percepts. Posterior alpha and beta desynchronizations are interpreted as reflecting bottom-up mechanisms which help to fulfill the endogenous reversals. It becomes obvious that patients depend more on the sensory input, which can be interpreted as a compensation of the inferior top-down control. The reduced gamma posterior synchronisation in the patient group while reversal processing is debated in literature in respect to inefficient binding to features. There are no obvious group differences for the gamma frequency in multistable processing. Significance: This is the first comparative study, that takes into account the event-related oscillations of all frequency bands during perceptual organization of the apparent motion. Therewith, dysfunctional integration processing in schizophrenia patients is investigated. Coherent perception of the environment originates from an intact interaction of sensory and cognitive processing. An understanding of altered oscillatory dynamics in schizophrenia may provide new insights in the pathomechanisms of the disorder.