Psychotic-like experiences in childhood and adolescence: A cognitive neuropsychiatric approach

Psychotic-like experiences (PLEs) include experiences such as hallucinations and delusional thinking that can occur in the absence of a clinical disorder. PLEs peak in middle childhood but appear to spontaneously remit in most children. Nevertheless, their presence, and particularly their persistence, are associated with an increased risk of developing later psychosis and poor psychiatric and social out- comes. However, the mechanisms by which they are generated during childhood are unclear. Existing models of psychosis cite early life experience and childhood neurodevelopment as important but often examine these retrospectively. Further- more, they suggest mechanisms for how psychotic experiences are generated that are assumed to apply across the lifespan. This assumption has remained untested, however. Consequently, in this thesis, I investigated neurocognitive mechanisms of PLEs in 9-10 year-old-children using data from the Adolescent Brain Cognitive Development (ABCD) study. In Study 1, I examined whether the established mechanistic risk factors in adult psychosis - affective symptoms, traumatic experiences, cognitive function, structural brain changes - are associated with PLEs using net- work analysis, finding only that depression-related symptoms were associated with PLEs. In Study 2, I tested whether fMRI activation in striatal reward pathways was associated with PLEs in children, as this is an established finding in adults. This study found no strong evidence for alteration to striatal reward pathways with a high likelihood that it was absent, rather than undetectable. Given the prognostic and aetiological important of persistence of PLEs, in Study 3, I tested affective, trauma-related, cognitive and striatal reward activation predictors of 1-year PLE persistence. Only depressive symptoms were substantial predictors. Depressive symptoms emerged as the strongest predictor of PLEs at this developmental stage, both cross-sectionally and longitudinally. The findings indicate that PLEs in child- hood are not a 'mini psychosis syndrome' and developmental-stage specific models of psychotic experiences in children are required.