Cerebral asymmetries and stimulus intensity relationships in EEG spectra of VEPs in unmedicated schizophrenic patients: relationships with Active and Withdrawn syndromes
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Active and Withdrawn syndromes in schizophrenia have been associated with different patterns of lateral asymmetry: higher left than right hemisphere activity in the Active syndrome and the opposite pattern in the Withdrawn syndrome. Here validation was explored with a power spectral analysis of the visual evoked potential recorded to flashes of five different intensities from primary sensory occipital cortex (O1, O2) and from temporal (T3, T4) cortex. Unmedicated schizophrenic patients were categorised as Active or Withdrawn syndrome by clinical ratings. Pattern of lateral asymmetry of electrodermal orienting responses was recorded and was found to be as predicted: larger on the left than right hand in the Active syndrome with the opposite pattern in the Withdrawn syndrome. Normal controls were also examined. At occipital placements the main results were in beta (18-22 Hz) in which (1), syndromes showed opposite asymmetry patterns consistent with predictions: higher power on the left in the Active syndrome and on the right in the Withdrawn syndrome and (2), there was an absence of normal stimulus intensity/beta power relations in the Withdrawn syndrome. The Active syndrome showed abnormal relations at the temporal location, reflected in high alpha activity (10-14 Hz), together with an abnormal asymmetry in 2-6 Hz activity in the direction of more slow wave activity in the right hemisphere, a lateral asymmetry consistent with the model. When compared with the controls the Withdrawn syndrome was dysfunctional at lower, sensory cortex, levels of processing while the Active syndrome was dysfunctional at higher, temporal cortex, stages of processing. Schizophrenic patients as a group were characterised by abnormal desynchronisation of left temporal activity.
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