BACKGROUND: Bipolar disorder (BD) carries high suicidality risk. While suicidal ideation (SI) correlates with evening chronotype, their joint neuroimaging mechanisms remain unclear. Unimodal MRI lacks sensitivity to detect coupled structural-functional abnormalities. We hypothesized BD patients with SI (BD-SI) would exhibit altered structural connectivity-functional connectivity (SC-FC) coupling versus BD patients without SI (BD-nSI) and healthy controls (HC), potentially correlating with chronotype.
METHODS: We recruited 138 BD-SI, 46 BD-nSI, and 280 HC. Resting-state functional MRI (rs-fMRI) and diffusion tensor imaging (DTI) data were acquired, and chronotype was assessed by Morningness-Eveningness Questionnaire (MEQ). Structural/functional connectivity and SC-FC coupling were compared across groups. Associations between SI, chronotype, and altered SC-FC coupling were examined in BD-SI group.
RESULTS: We found an altered functional connectivity (FC) network between 3 groups, involving the caudate nucleus, putamen, supplementary motor area, postcentral gyrus, inferior temporal gyrus and fusiform gyrus as important nodes. BD-SI patients demonstrated the most pronounced evening chronotype shift in MEQ total scores. BD-SI patients showed reduced SC-FC coupling in the triangular part of right inferior frontal gyrus (IFGtriang.R) compared to BD-nSI and HC, while both BD subgroups exhibited decreased coupling in the right olfactory cortex (OLF.R) relative to HC. The right amygdala (AMYG.R) displayed increased coupling in BD-SI versus BD-nSI, however, its nominal association with evening chronotype in BD-SI patients did not survive multiple comparisons correction.
CONCLUSION: Our study reveals changes in SC-FC coupling and a significant eveningness chronotype in BD-SI patients. This conjunction of physiological and clinical features warrants further investigation into chronotherapeutic strategies.
