Quantitative analysis of resting EEG recordings displayed an increased delta and/or theta activity, a decreased main frequency, a low mean alpha frequency (“hypofrontality”) and an increased beta activity in schizophrenia patients [15, 26]. In dependence of the type of measure (steady-state evoked potentials, amplitudes, induced oscillations, and resting state [40]), amplitudes and phases have been found to be abnormal in schizophrenia patients. A common pattern of the different brain oscillations in schizophrenia patients is a reduction in amplitude and altered phase synchronization in all frequency bands (with emphasis on the beta and gamma band activity) at rest, during sensory processing and cognitive tasks [38, 40]. Further evidence is provided by animal studies showing that the synchronization of brain oscillations depends on cortico-cortical connections within and between hemispheres [11, 40]. Therefore, the findings of impaired neural oscillation and the reduced phase synchronization in schizophrenia patients can be considered as a marker for a functional disconnectivity between different brain areas and for dysfunctional cortical networks [40].
