It has been suggested that SC shapes and constrains FC across the brain network at various spatial scales, while FC exerts influences on SC through the plasticity mechanism. Structural and functional connectivity provides different perspectives on brain function, and they are interrelated. Therefore, the combination of both structural and FC may help better understand the pathological mechanism of suicide behaviors. However, most previous studies in suicidal behavior focus on only a single modality, which might be insufficient to depict the pathological changes. Abnormalities in SC and FC have been reported in BD with attempted suicide behaviors. Structural connectivity (SC) can be mapped via DTI using white matter tractography, while functional connectivity (FC) can be quantified by the temporal correlation between blood oxygen level-dependent fMRI signals. The advent of brain imaging techniques such as diffusion tensor imaging (DTI) and functional magnetic resonance imaging (fMRI) provide the new avenue to probe the structurally and functionally interconnected brain network. Therefore, objective neural markers are in urgent need to identify and predict suicide attempts as early as possible. Besides, about 80% of persons who committed suicide would cover up their suicidal ideation to doctors or health providers. However, the current suicide risk identification, which mainly relies on clinical assessments such as interviews or scale, is unsatisfactory because of the subjectivity of retrospective clinical information and self-reports by patients. Given the high suicide risk in BD, early identification and intervention are particularly important in clinical practice. Based on the statistic, the estimated prevalence of suicide attempts in BD type I and BD type II was about 32.4% and 36.3%, respectively, which is ~20–30-fold greater than the general population. Such a measure can have clinical implications for early identification of suicide attempters with BD depression and inform strategies for prevention.īipolar disorder (BD), typically characterized by recurrent episodes of mania/hypomania and depression, is a mental disorder most associated with suicide, especially during the major depressive episode. Our findings suggest that the structural connectome is the key determinant of brain dysfunction, and structural–functional coupling could serve as a valuable trait-like biomarker for BD suicidal predication over and above the intramodality network connectivity. Crucially, the altered structural connectivity network predicted the abnormal functional connectivity network profile, and the structural–functional coupling was significantly correlated with suicide risk but not with depression or anxiety severity. By investigating structural and resting-state fMRI connectivity, as well as their coupling among 191 BD depression patients with or without a history of suicide attempts and 113 healthy controls, we found that suicide attempters in BD depression patients showed significantly decreased central-temporal structural connectivity, increased frontal–temporal functional connectivity, along with decreased structural–functional coupling compared with non-suicide attempters. Here, we hypothesize that structure connectivity constrains functional connectivity, and structural–functional coupling is a more sensitive biomarker to detect subtle brain abnormalities than any single modality in BD patients with a current major depressive episode who had attempted suicide. Although structural and functional connectivity alterations from neuroimaging studies have been previously reported in BD with suicide attempts, little is known about how abnormal structural and functional connectivity relates to each other. Bipolar disorder (BD) is associated with a high risk of suicidality, and it is challenging to predict suicide attempts in clinical practice to date.
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