Non-suicidal self-injury in adolescents : executive functions and the role of Serotonin in impulsivity

Abstract

In the last few decades, there has been an increased focus on non-suicidal self-injury (NSSI) in general and in adolescents in particular. Research findings show that NSSI is alarmingly widespread even in community samples of adolescents. Furthermore, NSSI is associated with psychological suffering, such as depression, suicidality, and anger problems, emphasizing the seriousness of this behaviour. However, little is known of underlying factors that can be involved in NSSI. In particular, research investigating the possible roles of neuropsychological and serotonin functions in NSSI in adolescents is scarce.<br> One main aim of this dissertation was therefore to investigate various aspects of neuropsychological functions in community sampled adolescents engaging in NSSI. Another main aim was to investigate the effects of low serotonin function on impulsivity and mood in female adolescents engaging in NSSI.<br> In paper I we report the results of our investigation of three main aspects of executive functions (EFs), i.e. shifting, updating (working memory) and inhibition, in a high-severity NSSI group (n=33), a low-severity NSSI group (n=29) and a healthy control group (n=35). The results indicate that NSSI subgroups have distinct deficits in EFs. The high-severity NSSI group has working memory deficits, while the low-severity NSSI group has impaired inhibitory control. This indirectly supports the emotion regulation hypothesis. As reported in paper II, we investigated various aspects of verbal learning and memory in adolescents engaging in NSSI (n=62) as compared with healthy controls (n=36). We found that adolescents engaging in NSSI exhibit impairments in verbal learning and memory. The core problems involve impaired short-term memory/working memory and difficulty in the encoding of material into long-term memory.<br> As described in paper III, we investigated the effects of experimentally lowered serotonin (5-HT) activity, via acute tryptophan depletion (ATD), on impulsive action, reflection impulsivity and mood in female adolescents engaging in NSSI. Thirty-two female adolescents engaging in NSSI participated in a randomized, double-blind, parallel group ATD study (active group: n=17; placebo group: n=15). Following ATD, female adolescents engaging in NSSI adopted an impulsive response style. In addition, ATD caused increased attentional capacity. Thus, the impulsive response style was characterized as being focused and directed, as one of functional impulsivity resulting in an optimal test performance. This finding might suggest that low serotonin function triggers this particular group of female adolescents to impulsively engage in NSSI when in emotional distress. This might possibly be relevant for emotion regulation in female adolescents engaging in NSSI. ATD did not affect reflection impulsivity or mood. The findings from this study help illuminate various aspects of neuropsychological and serotonergic functioning that seem to be involved in NSSI in adolescents. In a theoretical perspective, the findings yield knowledge about neuropsychological factors involved in NSSI, thereby contributing to the puzzle of understanding why adolescents engage in NSSI, at least from a neuropsychological perspective. Also, the findings from the study yield valuable knowledge about neuropsychological as well as serotonin functioning that should be targeted in applied and clinical settings to help adolescents discontinue engaging in NSSI as well as to reduce possible functional consequences of deficits in specific neuropsychological functions.