OBJECTIVES: To evaluate the coherence values of the cortical bands in patients with first episode schizophrenia and schizoaffective disorder during the performance of a mental arithmetic task. METHOD: We analysed EEG coherence in the resting state and subsequently while counting down from 200 in steps of 7 in 32 first episode schizophrenia patients (SZ), 32 patients with first episode schizoaffective disorder (SA) and 40 healthy controls (HC). RESULTS: Task performance in HC is characterised by decreased coherence in the alpha bands and increased coherence in the beta 2 and gamma bands in frontal sites. In SZ, coherence decreases in the alpha band, whereas in SA it substantially increases in the alpha, beta1, beta 2 and gamma bands. CONCLUSIONS: Despite no differences in performance on a behavioural level, SA patients demonstrate a paradoxical increase in both low and fast frequency bands during the performance of a mental arithmetic task, while, patients with SZ show a decreased coherence in the alpha band, presumably alluding to the excessive excitatory (in SA) and inhibitory (in SZ) mechanisms in cognitive processing. SIGNIFICANCE: The current study provides evidence for the distinction of neurophysiological mechanisms of cognitive processing between SZ and SA.

Department of Psychiatry and Psychotherapy 3rd Faculty of Medicine Charles University Prague Prague Czech Republic

Human Science Centre Institute of Medical Psychology Ludwig Maximilian University Munich Germany

Institute of Higher Nervous Activity and Neurophysiology of Russian Academy of Science Moscow Russian Federation

Moscow Research Institute of Psychiatry Branch of 5 Serbsky National Medical Research Centre for Psychiatry and Narcology Moscow Russian Federation

National Institute of Mental Health Klecany Czech Republic

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