Proactive and reactive cognitive control in adolescence and young adulthood: neural signatures and relationship with reward drive and maladaptive outcomes

Over the last two decades, there has been extensive research into adolescent brain development. This research has informed developmental models of adolescent behaviour. These models suggest that an increase in risk-taking behaviour during adolescence arises as a result of an underdeveloped cognitive control system, and an overactive reward system. However, evidence for these models is inconsistent. This thesis aimed to further develop our knowledge of the neural underpinnings of cognitive control and elucidate the relationships between cognitive control, reward drive, impulsivity, and outcomes across adolescence and young adulthood. The thesis extended our knowledge of the frontoparietal networks underlying proactive and reactive control using a cued-trials task-switching paradigm and concurrent electroencephalogram (EEG). Time-frequency power and event-related potential (ERP) analyses was performed on the EEG data to measure localised frontal and parietal activity. Time-frequency connectivity analyses were performed to measure global activity (i.e. connectivity between frontal and parietal regions) within frontoparietal networks. The first half of this thesis found that frontal and parietal power, and frontoparietal connectivity were associated with improved performance on the cued-trials task-switching paradigm in both proactive and reactive control periods. In line with previous research, the majority of these effects were in the theta band (~4-8 Hz). Then, using these localised power and global network measures, the second half of this thesis examined developmental differences in cognitive control and its neural underpinnings across adolescence into young adulthood, and how these differences relate to reward drive and outcomes. Frontal and parietal power and frontoparietal connectivity did not differ as a function of age. However, ERP components associated with task-switching were larger for adolescents compared to adults. The ERP, frontal and parietal power, and frontoparietal connectivity were only weakly related to reward drive or impulsivity. However, self-reported cognitive control ability significantly mediated the relationships between impulsivity and psychological distress, and impulsivity and quality of life. Interestingly, age did not moderate this effect. These findings demonstrate the importance of accounting for individual differences when investigating relationships between cognitive control, impulsivity, reward drive, and outcomes to produce a more individualised account of adolescent behaviour.