Large international neuroimaging studies have identified subtle brain differences associated with suicide attempts. The ENIGMA consortium found that people with a history of suicide attempts have, on average, slightly smaller volumes in certain deep brain regions, including the thalamus and pallidum. Surprisingly, these same differences have not been observed in people experiencing suicidal ideation. How can this paradox be explained?
Our research proposes an explanation grounded in the functions of these brain regions. The thalamus and pallidum are involved in emotional reactions, motivation, and spontaneous tendencies to act. Deliberate reflection and planning, by contrast, rely more heavily on prefrontal brain regions. Yet conventional clinical scales typically assess suicidal ideation along a continuum, from thoughts of death to detailed suicide plans, with greater planning treated as a sign of increasing severity. It may therefore be less surprising that the regions identified by ENIGMA were not associated with suicidal ideation when measured in this way.
We propose distinguishing two forms of suicidal ideation: “hot” thoughts, which arise in periods of intense emotional distress, with a sense of urgency and little planning, and “cold” thoughts, which are more deliberate and planned. Our hypothesis was that the ENIGMA brain findings would be more closely associated with the former than the latter.
To test this hypothesis, we examined structural MRI scans from 263 patients with major depressive disorder. Patients experiencing hot suicidal ideation had, on average, smaller volumes in the ENIGMA-defined regions than patients without suicidal ideation. No statistically significant difference was observed among patients with cold suicidal ideation. We also found no comparable association with the dorsolateral prefrontal cortex, a region more closely involved in reflection and cognitive control.
These findings suggest that suicidal thoughts may differ not only in severity but also in the psychological processes underlying them. They offer an initial explanation for the ENIGMA paradox: treating all suicidal thoughts as successive stages of one phenomenon may conceal brain differences specific to certain forms of ideation. Understanding suicidal thoughts may therefore require more than assessing how severe or frequent they are. Their nature matters too.
Article reference
Chatard, A., Le Tutour, T., Langbour, N., Jaafari, N., Doolub, D., Leblanc, P.-M., Besnier, M., Delbreil, A., & Harika-Germaneau, G. (2026). Hot suicidal ideation is associated with reduced ENIGMA-defined subcortical volumes in major depressive disorder. Journal of Affective Disorders, 415, 122482.