Delayed hemodynamic responses associated with a history of suicide attempts in bipolar disorder: a multichannel near-infrared spectroscopy study

Bipolar disorder (BD) is associated with a high risk of suicide compared with other psychiatric disorders. Recent studies using near-infrared spectroscopy (NIRS) reported frontotemporal functional abnormalities in BD. However, it remains unclear whether NIRS signal changes are associated with vulnerability toward suicide in BD. We recruited 20 patients with depressed BD with a history of suicide attempts (suicide attempters; SAs) and 28 control patients with BD who did not have a history of suicide attempts (non-attempters; NAs). Regional hemodynamic responses during a verbal fluency task were monitored using NIRS. Compared with the NA group, the SA group exhibited significantly reduced activation during VFT in the bilateral precentral and superior temporal gyri and left supramarginal, inferior frontal, postcentral, and middle temporal gyri. Furthermore, compared with the NA group, the SA group exhibited delayed activation timing of the NIRS signal in the prefrontal region. In BD patients, current suicide risk was noted to be significantly and positively associated with delayed activation timing of the NIRS signal in the prefrontal region. The findings of this study suggest that the observed specific NIRS signal pattern in BD patients is associated with vulnerability toward suicide.