Objective Research suggests that an abnormal neural reactivity to threat may be a risk factor for suicide, but little is known about this. The late positive potential (LPP) has been a measure of emotional reactivity in numerous studies. The purpose of this study was to explore the neural responses, of depressed adolescents at risk for suicide when facing predictable and unpredictable threats . Methods 26 depressed patients with suicidal ideation (SI) and 32 healthy controls (HC) were recruited, and viewed threatening and neural faces in predictable condition and unpredictable condition. Event-related potential (ERP) was recorded and Late Positive Potentials (LPPs, early: 400-600 ms; late: 600-1000 ms) were extracted were extracted to quantify the neural activity. MINI-kid 5.0 interview and self report questionnaire were used to make mental diagnosis and suicide behavior assessment for individuals. Furthermore, a 2*2*2 repeated measures ANOVA analyses were conducted to identify the risk factors of suicidal behavior. Results & Discussion Regarding early LPP, under predictable conditions, the response to threatening faces was found to be lager than that to neutral faces in both SI and HC group. In the unpredictable condition, the HC group still showed a lager response to the threatening faces than the neutral faces, but this difference disappeared in the SI group. This difference was not seen in late LPP. This suggests that in unpredictable situations, depressed adolescents with SI tend to interpret neutral interpersonal information as threatening, and thus invest more cognitive resources in the initial stages of emotional regulation. Conclusions These results suggest that convergent responses to threatening and neutral faces under uncertain conditions may be a potential neural mechanism for suicidal ideation in depressed adolescents.

suicide;threat;LPP