Neural evidence of disrupted self-referential processing in suicidal depression

Suicide remains a leading cause of death, highlighting the critical need to elucidate the neural mechanisms underlying suicidality. This study used an event-related potential (ERP) paradigm to examine whether depressed individuals with and without suicidal ideation show distinct processing patterns for clinically relevant self-referential content. During electroencephalography, depressed individuals with (n = 46) and without (n = 44) suicidal ideation, and healthy controls (n = 48), read first-person sentences ending congruently or incongruently with depression, suicidality, or neutral biographical experiences. Linear mixed-effects models assessed group and congruency effects across early (N170), semantic (N400), and reanalysis (P600) stages. For neutral biographical (vs. non-biographical) sentences, all groups showed the expected reduction in N400 amplitudes, but the suicidal group showed a reduced P600 response compared to the other groups. For depressive (vs. non-depressive) sentences, both depressed groups showed reduced N400 amplitudes relative to controls, along with increased P600 amplitudes; the suicidal group uniquely showed a reduced N170 response that scaled with suicidal ideation severity independent of depression severity. For suicidal (vs. non-suicidal) sentences, the suicidal group showed an attenuated P600 response relative to controls. Together, these findings suggest that depressed individuals, regardless of suicidality, show facilitated semantic processing (N400) and increased late-stage elaborative processing (P600) of depressive self-referential content, consistent with a negative self-schema. In contrast, individuals with suicidal ideation show early neural blunting (N170) to depressive content and attenuated late-stage processing (P600) of personally relevant neutral and suicidal content. These patterns highlight the sensitivity of ERP measures to suicide risk, potentially representing candidate neural correlates for future study.