EEG-spectra parameters distinguish pathophysiological and pharmacological influences on the EEG in treated schizophrenics.

Movement related EEG segments of one second duration were analyzed by Fast Fourier Transformation in the Bereitschaftspotential paradigm in 31 neuroleptic treated schizophrenics compared to 21 matched controls. Schizophrenics demonstrated a higher theta mean power density and center frequency together with a lower radius of gyration, skewness and kurtosis in the theta band than controls. The higher theta power in the faster frequency range of the theta band is probably due to neuroleptic medication, but the higher theta power in the lower frequency range may be related to the disease. In the alpha band the schizophrenic group differed from controls by a lower center frequency, higher radius of gyration and skewness. Both groups did not differ in the alpha mean power density. The lower center frequency reflects the fact that alpha activity is distributed towards the lower frequency range which seems to be a consequence of the neuroleptic treatment. The more widespread alpha activity (higher radius of gyration) in schizophrenics indicates less frequency stability, i.e., more desynchronized alpha rhythm which corresponds to a highly activated functional state. By means of the applied spectral parameters more detailed quantitative descriptions of the power distributions in each frequency band are available, allowing to test hypothesis in relation to underlying physiological processes.