Abstract
Some brain abnormalities persist at the remission phase, that is, the state-independent abnormalities, which may be one of the reasons for the high recurrence of major depressive disorder (MDD). Hence, it is of great significance to identify state-independent abnormalities of MDD through longitudinal investigation. Ninety-nine MDD patients and 118 healthy controls (HCs) received diffusion tensor imaging scanning at baseline. After 6-month antidepressant treatment, 68 patients received a second scan, among which 59 patients achieved full clinical remission. Differences in whole-brain structural connectivity (SC) between patients with MDD at baseline and HCs were estimated by two-sample t-tests. Masked with significantly changed SCs in MDD, two-sample t-tests were conducted between the remitted MDD subgroup at follow-up and HCs, and paired t-tests were implemented to compare the differences of SC in the remitted MDD subgroup before and after treatment. Significantly decreased SC between the right insula and the anterior temporal cortex (ATC), between the right ATC and the posterior temporal cortex (PTC), between the left ATC and the auditory cortex as well as increased connectivity between the right posterior cingulate cortex (PCC) and the left medial parietal cortex (MPC) were observed in the MDD group compared with the HC group at baseline (p < 0.05, FDR corrected). The decreased connectivity between the right insula and the ATC and increased connectivity between the right PCC and the left MPC persisted in the remitted MDD subgroup at follow-up (p < 0.05, FDR corrected). The decreased SC between the right insula and the ATC and increased SC between the right PCC and left MPC showed state-independent characters, which may be implicated in the sustained negative attention bias and motor retardation in MDD. In contrast, the decreased SC between the right ATC and the PTC and between the left ATC and the auditory cortex seemed to be state-dependent.
Highlights
Major depressive disorder (MDD) is characterized by a high rate of recurrence and a high rate of lifetime prevalence, which brings an enormous burden to the patients, families, health system and society [1]
We found four abnormal structural connections in depressed individuals at baseline as compared to healthy controls (HCs), which mainly distributed in the bilateral temporal lobe, the right insula, the left medial parietal cortex (MPC), the posterior cingulate cortex (PCC)
After 6-month antidepressant treatment, decreased connectivity between the right insula and the right anterior temporal cortex (ATC), and increased connectivity between the right PCC and the left MPC persisted in remitted patients, showing a stateindependent character
Summary
Major depressive disorder (MDD) is characterized by a high rate of recurrence and a high rate of lifetime prevalence, which brings an enormous burden to the patients, families, health system and society [1]. Qin et al explored the topological properties of structural brain networks of MDD and found that both current and remitted patients exhibited a decrease in node strength of the right insula compared with HCs [5]. Another investigation in patients with remitted geriatric MDD revealed an altered component including regions and SCs in the right hemisphere. The regions were mainly paralimbic (insula, parahippocampal gyrus, and superior/middle temporal gyrus), subcortical (hippocampus, caudate nucleus, putamen, pallidum, and thalamus) regions [6] Taken these findings together, abnormal SC with insula in MDD patients seems to show state-independent characters. Large-scale follow-up studies with a more extended period are needed to overcome these shortcomings
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