PhD defence L.R. (Lisa) Steenkamp

Dissertation in short:

Hallucinations and delusions, such as hearing voices, have long been viewed as signs of severe mental illness. However, epidemiological evidence revealed that these phenomena are surprisingly common in the general population – especially in young people. Youth with such psychotic experiences are vulnerable to a range of negative mental health outcomes later in life, including psychosis, anxiety, and depression. However, it is unclear why some youth develop psychotic experiences while others do not. In this thesis we studied the course, childhood risk factors, and adolescent outcomes of psychotic experiences in a population-based cohort from Rotterdam, the Netherlands. This cohort has followed several thousands of young people from birth onwards.

Three key findings emerged. First, we found that approximately 30% of 10-year old children report psychotic experiences. Nearly 80% of these psychotic experiences were no longer present at the age of 14 years. Psychotic experiences were more likely to be persistent in children with more psychopathology, lower self-esteem, and lower IQ. Second, we identified several risk factors of psychotic experiences: 1) structural brain differences, including smaller gray and white matter volume, 2) bullying victimization, bullying perpetration, and social rejection, and 3) maternal exposure to childhood trauma. Third, we found that childhood psychotic experiences were related to adverse outcomes in early adolescence. These included 1) poor school performance and 2) risk of suicidality and non-suicidal self-harm.