Different patterns of abnormal gamma oscillatory activity in unipolar and bipolar disorder patients during an implicit emotion task.

This study investigates the distinct patterns of local and long-range gamma oscillations between patients with bipolar disorder (BD) and major depressive disorder (MDD). Twenty BD patients, twenty MDD patients, and twenty normal controls participated in this study. For each participant, the event-related magnetoencephalographic responses while performing an implicit emotional task were recorded and processed with time-frequency analysis. Compared to normal controls, the BD patients exhibited the gamma power decease at the right frontal and prefrontal regions and yet gamma power increase at the right posterior temporal region. The abnormal long-range gamma oscillation between the right frontal and parietal-occipital region was also found. These results indicate that the BD patients may have hyperactivity in perceptual binding of emotional features and tend to be oversensitive to facial features. On the other hand, MDD patients displayed increased early gamma activity at the left anterior temporal region, which may imply their hyperactivated binding process of emotional features at corticolimbic regions. The distinct alterations of gamma patterns between the BD and MDD patients implicate that their impairments of binding processes are located at different regions. Gamma activity in the parietal and left posterior temporal regions may be a potential index to differentiate BD patients from MDD patients.