Drug dependence (DD) is a chronic relapsing disorder and a global health issue. However, current available treatments have limited success and relapse rates remain high. By better understanding the mechanisms that contribute to the development and perpetuation of drug dependence we can address the large unmet need for effective treatment of DD.
Seminal research highlighted the role of the reward pathway in DD. More recent studies have identified a key role of impulsivity in the pathophysiology of DD. Impulsivity is a multidimensional construct and it remains unclear which dimensions are present at which stage of DD. This thesis aimed to characterise the role of impulsivity in DD.
Impulsivity measures were higher in polydrug dependence (PD) and methadone-maintained opiate dependence (MD) compared with healthy controls (HC). In general, alcohol dependence (AD) did not differ from HC. Trait impulsivity was associated with length of abstinence though methadone may have an effect on this association. Choice impulsivity was associated with the age of initiation of alcohol. Reward processing in frontal regions was associated with all measures of impulsivity and such associations differed between AD, PD and HC. rsFC between regions involved in impulse control and those involved in reward processing differed between DD groups and HC. Choice impulsivity was associated with these changes.
The results of this thesis confirm the prevalence of impulsivity in DD. Further, the data suggest that different domains of impulsivity can be used diagnostically and prognostically to predict vulnerability to DD and successful abstinence. The associations between impulsivity measures with reward and rsFC point towards the benefit of including impulsivity assessment in treatment planning and matching therapeutic interventions to individuals. Further work is needed to determine brain correlates of impulsivity domains and the role of impulsivity measures in relapse.