Topographic and energy analysis of resting MEG and photic stimulation responses in control subjects and patients with schizophrenia

To investigate sequential changes in magnetoencephalograms (MEGs) during photic stimulation (PS), we performed a quantitative MEG analysis of the alpha band (related to stimulus frequency) in 19 schizophrenic patients and 18 gender- and age-matched control subjects. Photic stimulation was at an interval of 0.5 Hz, and the frequency band was from 8 to 10.5 Hz. In each session, the interval lasted ten seconds and was repeated ten times for each frequency. In the topographic study, we assessed the differences between the two groups under two conditions (i.e., during PS and inter-PS). During the stimulus, the absolute 8-10.5 Hz band energy of the patient group was higher at the posterior sites throughout the ten-second periods. We compared the energy intensity of each site based on international 10/20 derivation. The energy intensity in the schizophrenic patients was smaller than in the control subjects at each site. We observed a gender difference in the control subjects, but not in the schizophrenic ones. These results suggest that schizophrenic patients show fewer changes in alpha activity during the stimulus, and this continuity of posterior dominance may reflect hyperarousal, which counteracts any decrease in vigilance throughout the PS