Traumatic brain injury and substance use disorder in Aotearoa New Zealand : characteristics, correlates, and the role of social cognition in an inpatient addictions treatment sample : a thesis presented in partial fulfilment of the requirements for the qualification of Doctor of Clinical Psychology at Massey University, Wellington, New Zealand

Abstract

Traumatic Brain Injuries (TBIs) and Substance Use Disorder (SUD) often cooccur, yet the underlying mechanisms linking these conditions remain unclear. One potential explanation is that TBI disrupts neuropsychological functioning, particularly Social Cognition, thereby increasing the risk of SUD. The overall objective of this thesis is to explore these relationships in depth. To achieve this, the first study aimed to gather a detailed history of head-injury characteristics among individuals with SUD in Aotearoa, including TBI with loss of consciousness (LOC). By ascertaining these characteristics, the second study aimed to examine their association with neuropsychological outcomes. Third, our final study aimed to explore the potential role of Social Cognition in explaining the relationship between TBI and SUD. A total of 77 adults (aged 18-64) engaged in residential treatment for SUD, participated in the current research. During their residential treatment program, participants completed self-report questionnaires to ascertain head-injury, TBI and SUD history, mental health, and TBI-related symptom severity. Of this sample, 70 went on to complete neuropsychological tasks. Study 1 revealed that one hundred percent of the sample endorsed one or more lifetime head-injury events. 81.8% of the sample had experienced a self-reported TBI featuring LOC, with the remaining 18.2% having a history of a ‘possible TBI’ where they sustained a head-injury event without LOC. Overall, 91% sustained multiple lifetime head-injuries (either with or without LOC). Compared to the general New Zealand population, this sample featured a higher rate of TBIs of moderate severity, and most events were untreated. Many individuals sustained head-injuries at a young age and sustained repeated injuries into adulthood. Study 2 found that individuals who had a high number of lifetime head-injuries showed significantly lower scores on executive functioning and self-reported experiencing more cognitive difficulties. Study 3 found that within Social Cognition, the interpretation of complex social cues, particularly those involving deception and subtle social intentions, may mediate the relationship between TBI and SUD. This research contributes to identifying unique rates, patterns, and outcomes of head-injury including TBI among treatment-seeking substance users and highlights factors which may increase individuals’ vulnerability. Social Cognition appears to be a mechanism worthy of future exploration as it may explain the relationship between TBI and SUD. Implications of these results for treatment and rehabilitation and directions for future research are discussed.