Structural and Functional Correlates of the Sleep-Suicidal Ideation Association

Each year, about 800,000 individuals die by suicide globally, affecting millions more. Mitigating suicide risks by targeting modifiable factors such as the sleep disturbances of insomnia and nightmares, which are prevalent and linked to suicidality is important. This study investigated the structural and functional brain differences related to sleep disturbances and suicidality, with the anterior cingulate (caudal and rostral), insula, middle frontal gyrus, posterior cingulate, thalamus, amygdala, and orbitofrontal cortex as seed regions. Participants had no history of suicidal ideation (NSI; n=43) or suicidal ideation within the past two weeks (SI; n=25). Measures for analyses included the Insomnia Severity Index (ISI), Disturbing Dream and Nightmare Severity Index (DDNSI), and Frequency of Suicidal Ideation Inventory (FSII). The relationships between group (control vs suicidal ideation), structural measurements (cortical surface area, cortical thickness, gray matter volume), insomnia and nightmares across the eight regions in each hemisphere were examined. Functional connectivity-change differences were measured across wake and sleep with the eight regions as seeds. The SI group had smaller cortical surface area and gray matter volumes in the left insula (t= 2.58, p = 0.012; t = 2.44, p = 0.017); however, not after adjusting for multiple comparisons. ISI and FSII total scores correlated with each other and the surface area and gray matter volume of the left insula. In a mediation model, ISI total score was significantly related to insula surface area and FSII total score (p = 0.023; p =0.027), but the insula surface area was not significantly associated with FSII total score (p = 0.075). The indirect effect of ISI on FSII through the left insula surface area was not significant (p =0.161). The SI group had smaller changes from wake to sleep than the NSI group in the functional connectivity of the right thalamus to the left and right superior/middle temporal regions. Other neurological mechanisms could be at play as only the cortical surface area and gray matter volume in the left insula had implied differences between groups and the structural differences did not mediate the relationship between insomnia and suicidality. Smaller functional connectivity-changes differences across wake and sleep for SI compared to NSI, potentially indicate deficits in auditory inhibition.