Discussion
unilaterality, anomalies, cognitive dysfunction, depressive symptoms, MDD, goal-oriented cognitive
REMISSION
This study explored FC changes in the CEN, SN and DMN among patients with rMDD, and compared FC between these patients and HCs at baseline and six months later. Compared with HCs, patients with rMDD had abnormal FC within the CEN, SN, and DMN at baseline. This residual aberrant network connectivity confirms findings from previous studies [There were anomalies in many CEN areas at the six-month follow-up; specifically, the IPL and DLPFC. Higher FC of the left IPL and right DLPFC at baseline were reduced at follow-up, and higher FC of the right IPL disappeared, possibly representing recovery from MDD. Previous studies have shown that the IPL and DLPFC are involved with self-concept and execution [The difference between the left and right IPL in the CEN may be due to the latter’s unilaterality. The CEN consists of two symmetrical networks, with the left and right differing in function [In the SN and the DMN, the insula, left anterior cingulate, right precuneus, IPL, and right mPFC had abnormal baseline FC in the rMDD group. Previous studies have shown higher FC of the precuneus [FC results in the CEN, SN, and DMN may mean that although there are residual symptoms at baseline, recovery is still possible. Changes in these three networks all seem to reflect improvement trends. Differences between baseline and follow-up BDI scores also suggest substantial improvement in depressive symptoms among patients with rMDD over time. This study showed that among these networks, the DMN may undergo the greatest recovery during initial remission, and that abnormalities gradually remit across remission, with only CEN abnormalities remaining after six months. This would suggest that goal-oriented cognitive control activities may play an important role in remission.Correlation analyses herein also suggest the importance of social functioning, which current evaluation systems overlook. Although these results show that FC of the CEN is related to psychosocial functioning, symptom scores may better reflect post-remission differences compared with psychosocial functioning assessments. While it may not be appropriate to replace all symptom assessments with psychosocial functioning assessments for determining remission, this construct should certainly be considered a factor.Further research will be needed to establish the mechanisms of rMDD recovery. To achieve this goal, it will be necessary to analyze more factors, assess patients longitudinally, and develop multifactorial evaluations. For both diagnosis and treatment, development of a more comprehensive measurement tool might be valuable, such as combining brain-level and functional symptom-level analyses, and following up on evaluation results. A more appropriate diagnostic criteria may include diagnoses and evaluations at different post-remission intervals, and organizing more comprehensive inquiry structures for those in remission. Personalized treatments should also be offered to patients at different stages.This study was not without limitations. The sample size affects its generalizability, as does use of a six-month follow-up. The latter may have led to selection bias, by including only patients who were highly cooperative. The lack of follow-up with HC participants disallowed complete exclusion of time factors as potential influences. The lack of examining relationship between functional connectivity and residual cognitive dysfunction. The effect of drugs on the results was not taken into account. Finally, ICA confers specific limitations like subjective bias in component identification.