Severity-dependent and -independent brain regions of major depressive disorder: A long-term longitudinal near-infrared spectroscopy study

Abstract Background Long-term longitudinal studies are necessary to establish neuroimaging indicators which contribute to the detection of severity changes over time in patients with major depressive disorder (MDD). Methods One hundred sixty-five patients with MDD underwent clinical assessments and near-infrared spectroscopy (NIRS) examination at the initial evaluation (T0). After 1.5 years, 45 patients who visited for the follow-up evaluation (T1.5) were included in the analysis. The authors conducted analyses using the 17-item Hamilton Rating Scale for Depression (HAMD) scores and mean oxy-hemoglobin concentration ([oxy−Hb]) changes during a cognitive task in NIRS at T0 (T0_HAMD, T0_[oxy−Hb]) and at T1.5 (T1.5_HAMD, T1.5_[oxy−Hb]), and their intra-individual longitudinal changes (ΔHAMD = T1.5_HAMD − T0_HAMD, Δ[oxy−Hb] = T1.5_[oxy−Hb] − T0_[oxy−Hb]). Results For severity-dependent regions, the Δ[oxy−Hb] in the right inferior frontal gyrus (IFG) was negatively correlated with the ΔHAMD. For severity-independent regions, the intra-class correlation coefficients between T0_ and T1.5_[oxy−Hb] were moderate in the bilateral middle frontal gyri (MFG). Limitations The percentage of patients included in the follow-up examination was relatively small. Conclusions Brain activation in the right IFG and the bilateral MFG as measured by NIRS may differentially indicate clinical severity and trait-related abnormalities in MDD.