Abstract
Although suicide is the second-leading cause of death in adolescents and young adults worldwide, little progress has been made in developing reliable biological markers of suicide risk and suicidal behavior. Converging evidence suggests that excitatory and inhibitory cortical processes mediated by the neurotransmitters glutamate and γ-aminobutyric acid (GABA) are dysregulated in suicidal individuals. This study utilized single- and paired-pulse transcranial magnetic stimulation (TMS) to assess excitatory and inhibitory cortical functioning in healthy control adolescents (n = 20), depressed adolescents without any history of suicidal behavior (“Depressed”, n = 37), and depressed adolescents with lifetime history of suicidal behavior (“Depressed+SB”, n = 17). In a fixed-effects general linear model analysis, with age, sex, and depression severity as covariates, no significant group main effects emerged for resting motor threshold, intracortical facilitation, short-interval intracortical inhibition, or cortical silent period. However, group main effects were significant for long-interval intracortical inhibition (LICI) at interstimulus intervals (ISIs) of 100 ms and 150 ms, but not 200 ms. Depressed+SB adolescents demonstrated impaired LICI compared to healthy control and Depressed adolescents, while healthy control and Depressed participants did not differ in LICI. Multiple linear robust regression revealed significant positive linear relationships between lifetime suicidal behavior severity and impairment in LICI at 100-ms and 150-ms ISIs. In a post hoc receiver operating characteristic analysis, LICI significantly discriminated Depressed from Depressed+SB youth in 100-ms and 150-ms paradigms. These findings suggest that GABAB receptor-mediated inhibition is distinctly dysregulated in depressed adolescents with histories of suicidal behavior. Further research is warranted to establish the utility of cortical inhibition in the assessment of suicide risk and as a target for treatment interventions.
Highlights
Suicide is the second most common cause of death among adolescents and young adults in the United States [1] and globally [2], with 17.7% of U.S adolescents reporting having seriously considered suicide, 14.6% having made a suicide plan, and 8.6% having attempted suicide within the preceding 12 months [3]
Societal, and healthcare burdens associated with suicidal behavior in young people, assessing suicide risk remains a challenge in clinical practice, frequently complicated by the lack of objective, verifiable data
A list of concurrent psychotropic medications taken by participants in the Depressed and Depressed+suicidal behavior (SB) groups at the time of TMS testing is provided in Supplementary Table S1
Summary
Suicide is the second most common cause of death among adolescents and young adults in the United States [1] and globally [2], with 17.7% of U.S adolescents reporting having seriously considered suicide, 14.6% having made a suicide plan, and 8.6% having attempted suicide within the preceding 12 months [3]. Suicidal ideation and attempts during childhood and adolescence predict later suicidal behavior in adulthood [4]. Rates of suicide attempts among adults have increased in recent years [5]. Societal, and healthcare burdens associated with suicidal behavior in young people, assessing suicide risk remains a challenge in clinical practice, frequently complicated by the lack of objective, verifiable data. The predictive value of identified suicide risk factors, is limited and has not improved substantially over time, despite decades of research [6]. There is growing recognition of the need for additional quantifiable neurobiological markers to augment current clinical assessments in order to more reliably identify and monitor those at high risk for suicide [8, 9]
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