Suicide Risk Markers in Major Depressive Disorder: a Study of Electrodermal Activity and Event-related Potentials

Background: Globally approximately 1 million people die annually by suicide. We studied both Electrodermal Activity (EDA) and Event-Related Potential (ERP) P3, together with an assessment of expressed anger as potential suicide risk predictors in Major Depressive Disorder (MDD) patients.

Methods: In this controlled cross-sectional study, MDD inpatients were allocated to one of three groups: 1. history of 'hard attempted suicide' (e.g., hanging, stabbing; HAS), 2. 'soft attempted suicide' (poisoning; SAS) or 3. no attempted suicide (NAS), respectively. Patients were tested using both an auditory habituation paradigm (study 1) and an 'oddball task' (study 2). EDA Habituation Rate (HabR) and P3 amplitude differences evoked by both 'novel' and 'target' stimuli were computed between the first and second halves of the two studies. 'Anger' was assessed using State Trait Anger Expression Inventory (STAXI) subscales.

Results: HabRs in both HAS (n=16) and SAS (n=16) were significantly lower than in NAS (n=18), in both study 1 and study 2, condition 'novel'. Decreases in P3 were also more pronounced in the HAS and SAS groups in study 1 and in the HAS group in study 2, 'novel' and 'target' condition. STAXI Anger In score was higher in HAS than in NAS.

Limitations: The sample size is small; medication may influence EDA.

Conclusions: Both EDA and P3 habituated faster in MDD patients with a history of attempted suicide, and were associated with higher 'anger' scores. Our data is a starting point for developing further neurobiological assessments of suicide risk in clinical practice.