Parahippocampal network dysfunction distinguishes suicidal ideation from suicide attempts in adolescents with major depressive disorder: a cross-sectional resting-state fMRI study

Adolescents with major depressive disorder (MDD) frequently experience suicidal ideation (SI) and are at elevated risk of progressing to suicide attempts (SA). Consequently, identifying neural mechanisms that differentiate SI from SA is critical for early risk detection. We acquired resting-state functional magnetic resonance imaging (fMRI) data from 106 adolescents with MDD, categorized into SI only, SA only, both suicidal ideation and suicide attempts (SIA), and no suicidal ideation or suicide attempts (NS), along with 23 healthy controls (HC). Graph theoretical analysis and seed-based functional connectivity (FC) analysis were applied to examine network alterations and their clinical associations. The SI and SIA groups showed reduced nodal clustering coefficient (NCp) in the left parahippocampal gyrus (PHG) and reduced nodal degree centrality in the right PHG. Compared with the SA and HC groups, the SI group demonstrated reduced FC between the bilateral PHG and the lateral temporal cortex. The FC between the PHG and the sensorimotor network in the SI and SIA groups was significantly lower than that in the NS and HC groups. PHG-centered network alterations were associated with current SI in adolescents with MDD, highlighting the potential role of the PHG in suicide risk assessment. Weaker PHG connectivity with lateral temporal and sensorimotor regions may reflect differences in mnemonic–perceptual and sensorimotor integration. Given the cross-sectional design and small, unequal subgroups, these preliminary findings require validation in larger longitudinal and multimodal studies.