[Quantitative EEG characteristics of the state of depressive phase and the state of remission in major depression].

We conducted a comparative study by using quantitative EEG analysis to clarify quantitative characteristics and possible markers of major depression. The subjects included 27 patients with major depression with melancholic features (DSM-III-R) (hereafter referred to as depressed group), 21 patients in the state of remission (hereafter referred to as remission group) and 17 subjects with no psychiatric disorder (hereafter referred to as control group). All participants were right-handed. All depressed group patients received medication treatment and all remission group patients had maintenance antidepressant medication. EEGs were recorded from the 16 electrode sites of the international 10-20 system while the subjects were at rest with their eyes closed. Artifacts rejected EEGs which were obtained from the bilateral frontal (F3, F4) and parietal (P3, P4) regions were analyzed on off-line with Fast Fourier Transform. The mean values of absolute amplitude power were calculated for 180 seconds (90 segments x 2 seconds), and derived for the following frequent bands: theta 1 (4.0-6.0 Hz), theta 2 (6.0-8.0 Hz), alpha 1 (8.0-10.5 Hz), alpha 2 (10.5-13.0 Hz), beta 1 (13.0-20.0 Hz) and beta 2 (20.0-40.0 Hz). Based on these values, the following parameters were calculated: F-Index "((F4-F3)/(F4+F3)) x 100" indicating relative predominance of the right side in the frontal region, P-Index "((P4-P3)/(P4+P3)) x 100" indicating relative predominance of the right side in the parietal region, and Left or Right PF-Index "((P-F)/(P+F) x 100" indicating relative predominance of parietal region to the frontal region on the left or right hemisphere. Compared with the control group, the remission group showed less theta 1 and alpha 2 power in the bilateral frontal regions and less right predominance in alpha 1 power in the parietal regions. Compared with the depressed group, the remission group showed less theta power in the bilateral frontal regions. Compared with the control group, both the depressed and remission groups showed higher beta 2 power in the bilateral frontal regions. These results may be considered as a trait dependent phenomena of major depression, although the effects of age and medications may affect these results. Both the depressed group and the remission group showed the parietal predominance in alpha 1 power in the left hemisphere. These results also may be considered as a trait dependent phenomena of major depression. For the next analysis, we calculated Left or Right PF-Index from the mean absolute amplitude power in the alpha 1 band. The indices were then plotted on a coordinates with Left PF-Index as the X axis and Right PF-Index as the Y axis. On the PF-Index coordinates, 93% of the depressed group patients and 86% of the remission group patients were plotted in the same areas. These areas which show their predominance of parietal to frontal are lower in the right hemisphere than in the left hemisphere, and the location of these areas on the coordinates were different from that of the control group. These results are consistent with our previous studies of depressed patients without receiving medication treatment. Our findings show the deviation of the inter and intra-hemispheric relationships is present not only in the state of depressed phase but also in the state of remission. Therefore, the inter- and intra-hemispheric relationships, depicted on the PF-Index coordinates, could be used as a trait marker of a major depressive disorder.