Cognitive Behavioral Therapy (CBT) Study Evaluating the Updating of Persecutory Beliefs

The purpose of this study is to examine how Bayesian belief updating changes throughout psychotherapeutic treatment for persecutory delusions. Specifically, individuals with a psychotic disorder diagnosis who endorse both a current persecutory delusion with strong conviction and significant worry will be recruited and randomized to receive either a CBT-based worry intervention for persecutory delusions or an active control condition (befriending therapy). The investigators will examine: 1) whether belief updating parameters change as delusion severity changes, 2) whether CBT contributes to greater change in belief updating parameters than befriending therapy, and 3) whether neural correlates of belief updating parameters, as measured using functional magnetic resonance imaging (fMRI), predict treatment response.