| Summary: | Externalising problems are some of the most common disorders in childhood and adolescence, and predict worse criminal, social, and academic outcomes during adulthood. These externalising behaviours have been associated with an imbalance between approach/reward systems and avoidance/punishment systems. This imbalance is thought to express itself as behavioural disinhibition, empathic blunting, and reward dominance. However, whilst recent neuroimaging studies have begun to investigate functional changes surrounding externalising behaviours, we know little about the underlying neural mechanisms these changes reflect. This is especially true of feedback processing where the literature has been limited to haemodynamic methodologies, which may blur distinct events related to feedback processing. The primary aim of this thesis was to investigate differences in reward and punishment processing associated with externalising behaviour amongst both normative and clinical samples. Electroencephalogram (EEG) recordings were taken during feedback tasks and analysed in both the time domain and time-frequency domain. Results from typically developing participants revealed that high externalising was associated with increased motivational salience of reward feedback compared to punishment feedback, and deficits in error monitoring processes. By comparison, high externalising behaviour amongst clinical participants was associated with differences in EEG signals of error-monitoring, but no differences in the motivational significance of reward and punishment. However, given the social elements of the Taylor Aggression Paradigm, where participants competed against fictitious opponents, these results may partially reflect differences in the ecological validity of the tasks used. This lack of consistency between normative and clinical samples highlight the need for research investigating externalising related changes in approach and avoidance behaviours in both social and non-social circumstances.
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