Resting-state EEG default mode network connectivity and suicidal ideation in depressive disorders: a retrospective cross-sectional study

BACKGROUND: Suicide remains a critical global public health issue, and the ideation-to-action framework suggests that suicidal ideation and attempts involve distinct processes. However, the neurobiological mechanisms underlying the transition from suicidal ideation (SI) to suicide attempts (SA) have not been fully understood, particularly in clinically heterogeneous psychiatric populations. This study aimed to investigate whether resting-state electroencephalography (EEG) connectivity patterns can differentiate suicidal ideation and attempts. METHODS: Resting-state functional connectivity as measured by EEG was analyzed among 244 participants, categorized into three groups: non-suicidal, suicidal ideation only, and suicide attempt. The analysis focused on the default mode network (DMN) and inhibition network using source-level analysis. Group differences were examined first in the full sample and then repeated in the depressive disorder subgroup (N = 78) to evaluate whether findings were more evident within a diagnostically more homogeneous context. RESULTS: In the full sample, no significant group differences survived either global or network-based false discovery rate correction in either network. In the depressive disorder subgroup, however, the suicidal group (SI + SA) showed reduced theta-band functional connectivity within the DMN, particularly between the dorsomedial prefrontal cortex and right inferior parietal lobule, compared with the non-suicidal group. No significant differences were observed between the SI-only and SA groups, and no significant findings emerged in the inhibition network. CONCLUSIONS: Altered DMN connectivity may be relevant to suicidal ideation in depressive disorders, while inhibition-network connectivity did not differentiate SA from SI-only. These findings are broadly consistent with aspects of the ideation-to-action framework and highlight the importance of considering diagnostic context when interpreting resting-state EEG findings in suicide research.