Topographic analysis of EEG photic driving in normal and schizophrenic subjects.

In a 19-channel EEG photic driving paradigm the steady-state evoked response was studied in schizophrenic patients and normal controls. Seventeen drug-free patients and 15 normal controls were compared. Schizophrenic patients had lower EEG photic driving in the alpha range, particularly in the high alpha frequency band (p = 0.08). Topographic analysis revealed that the group differences were primarily located in the mid-frontal, central and parietal areas (p < 0.05). Temporal and lateral frontal lobe alpha remained the same in the two groups. Separate analysis of eye movement (EM) showed an opposite effect on the alpha-frequency photic driving as compared to that on the resting alpha EEG. EM decreased the resting alpha EEG and increased the photic driving. This finding suggested that the lower EEG photic driving in the schizophrenic patients could not be explained by the eye movement artifact. We hypothesize that the 10 Hz range photic driving that reflects the intrinsic EEG spindle generation in the thalamus may play an important role in the psychophysiology of schizophrenia.