More optimal but less regulated dorsal and ventral visual networks in patients with major depressive disorder.

Previous studies indicate that major depressive disorder (MDD) can profoundly modify the visual cortices as well as the visuo-attentional systems of brain. However, little is known on the specific pattern of the whole-network-level abnormalities. In this study, resting-state functional magnetic resonance imaging data were collected from 159 participants, including 86 medication-free MDD patients and 73 matched healthy controls. The dorsal/ventral visual networks were defined based on our previously published brain coordinates from activation likelihood estimation analyses. The static and dynamic network properties were respectively calculated and compared between MDD and control groups. Moreover, the inter-network connectivities quantified using the multivariate distance correlation between the dorsal attention network (DAN) and the two visual networks were also analyzed. Results indicated that both of the two visual networks in MDD were found with significantly increased clustering coefficient (dorsal: p = 0.002; ventral: p = 0.004) and higher small-worldness (dorsal: p = 0.001; ventral: p = 0.002) as compared with control group. A higher mean variability of dynamic functional connectivity was found in both two networks in MDDs (dorsal: p < 0.001; ventral: p = 0.001). Moreover, the two visual networks in MDD group showed decreased inter-network connectivities to DAN (dorsal: p = 0.004; ventral: p = 0.013). Taken together, these results may support that the ventral and dorsal visual systems under the pathological effect of depression are possibly characterized by a status of increased autonomy, i.e., a more optimal, economical, and efficient intra-network organization combining with increased independency and receiving less outside regulation from attention network, thus indicating the increased functional role of the brain visual systems in MDD.