| Description: |
Formal Thought Disorder (FTD) is a core symptom of schizophrenia, and is a part of disorders of thought, language and communication. It represents the inability for an individual to create, organize and produce a coherent speech. If this symptom is severe, individuals with schizophrenia face multiple poor clinical outcomes. Moreover, the most frequent comorbidity associated with schizophrenia is cannabis use. Indeed, about one in four individuals with schizophrenia also meets the criteria for cannabis use disorder. Cannabis use is considered both a risk factor for developing psychotic disorders and an aggravating factor of psychotic symptoms. This thesis investigates one essential question: is FTD more severe in the presence of cannabis use among individuals with schizophrenia?This thesis uses two approaches to investigate this question: a clinical data-based approach, and a neuroimaging data-based approach. In the first chapter, we demonstrate that individuals with schizotypal traits, first-episode psychosis and schizophrenia display more severe FTD in the presence of cannabis use compared to non-users, using a systematic review and meta-analysis design. Next, we jointly explore all clinical symptoms of schizophrenia and account for variables that could affect the results, via a meta-analysis on individual participant data, totaling over 3000 individual participant data. We thus show the two-fold association, both positive and negative, of cannabis use with the severity of multiple symptom dimensions. A causal role of cannabis cannot be inferred from these results, it can, however, support the theory for the potential dual role of cannabis in schizophrenia, both harmful and protective.The neuroimaging data-based approach presented in chapter 2 investigates neural correlates of FTD using an experimental design. In this study, we recruited 50 individuals with schizophrenia, divided in 25 cannabis users and 25 nonusers. The preliminary results of this study did not show any significant association between clinical ... |