In this study, we investigated the pathophysiology of major depressive disorder (MDD) and of bipolar disorder (BD) by using near- infrared spectroscopy (NIRS) and magnetoencephalography (MEG). The study participants were segregated into 3 groups : the MDD, BD, and healthy control (HC) groups. During the verbal fluency task, compared to the HC group, the MDD group showed hypoactivation in the frontal lobe and the BD group showed delayed activation. During the talk and listen phases of the conversation task, the MDD group showed hypoactivation in the frontal lobe while the BD group did not show rhythmic [oxy - Hb] changes. The MDD and BD groups had lower mismatch field (MMNm) amplitudes indexing automatic attention; the duration of MMNm was prolonged only in the BD group. These results indicate that frontal activation decreased in the MDD group and was delayed in the BD group. The altered frontal activation in the MDD and BD groups may have been caused by the impairment at the level of automatic attention; however, further studies are required to confirm this issue.