Non-Suicidal Self-Injury, Alcohol Use and Impulsivity Among Young Adults

Non-suicidal self-injury (NSSI), the deliberate destruction of one’s own body tissue without conscious suicidal intent, is a concerning public health problem that is most prevalent among youth. NSSI is a known risk factor for suicide and has been linked to a range of negative physical and mental health outcomes. NSSI co-occurs with problematic alcohol use, and this potentially harmful combination of behaviours has been associated with a heightened risk of suicide. Despite the known links between NSSI and problematic alcohol use, their association is not well characterised. Impulsivity, broadly defined as the tendency to engage in rash and ill-advised behaviours, has been independently linked to both NSSI and alcohol use and may therefore represent a potential behavioural mechanism underlying their association. Impulsivity can be conceptualised from two perspectives: as a personality trait, which regards facets of impulsivity as stable personality traits over time and across situations; and also as a cognitive process which views impulsivity as a cognitive operation sensitive to current internal and external demands. Trait impulsivity is typically measured using self-report scales, while cognitive impulsivity is measured using objective neurocognitive tasks. The two empirical studies reported in this thesis aimed to broadly examine how different forms of impulsivity (trait and cognitive impulsivity) contribute to NSSI and co-occurring problematic alcohol use among young adults. Specifically, the aim of study one was to determine which facets of trait impulsivity are elevated in individuals who engage in both NSSI and problematic alcohol use compared to individuals who engage in just one of these behaviours, and those who engage in neither. While individuals engaging in self-injury have consistently reported higher trait impulsivity, the cognitive aspects of impulsivity (e.g., motor and choice impulsivity) that may be relevant in real-life contexts are not well understood. Given that self-injury typically occurs in the context of negative emotional states, increases in cognitive impulsivity may primarily emerge in such emotional contexts. The aim of study two was to determine whether a psychosocial stress manipulation increased cognitive impulsivity in young adults engaging self-injury compared to those with no history of self-injury. Unlike study one, the second study focused explicitly on two comparison groups to examine the fundamental impulsivity mechanisms in young adults who engage in NSSI. Young adults aged between 18 to 30 years were recruited for both studies. Study one was a cross-sectional study that comprised 349 young adults who completed self-report questionnaires assessing alcohol use, engagement in self-injury, and trait impulsivity. Results showed that positive urgency and sensation seeking traits were elevated in young people who engaged in both NSSI and problematic alcohol use relative to those who engaged in NSSI only. Negative urgency was elevated among individuals who engaged in NSSI, problematic alcohol use and both behaviours compared to a healthy comparison group. Study two included experimental tasks to assess cognitive impulsivity among 64 young adults; 32 who had a history of self-injury, and 32 who had no history of self-injury. Participants completed two computerised cognitive tasks: the Stop Signal Task (SST) and the Delay Discounting Task (DDT), before and after the induction of stress using the Trier Social Stress Test (TSST). Study two revealed that after experiencing a stressful situation, individuals who self-injure exhibited greater motor impulsivity but there were no differences in choice impulsivity between groups. These findings indicate that individuals who self-injure have specific difficulties to stop prepotent motor actions when under stress. The findings reported in this thesis are relevant to understanding impulsivity in individuals who engage in NSSI and co-occurring alcohol use, and provide useful insights that may guide interventions aimed at taming impulsivity among individuals engaging in risky behaviours.