Our research investigates alterations in brain structure and function in psychiatric disorders. The focus is on obsessive-compulsive disorder and schizophrenia which are both characterized by structural brain changes and alterations in brain activity and behavior. Patients with schizophrenia suffer from positive symptoms such as hallucinations as well as negative symptoms such as attentional and learning deficits which lead to severe everyday life impairments. Using functional MRI and diffusion tensor imaging (DTI) we try to find out more about the structural and functional correlates of these deficits. We moreover apply multi-modal imaging combining functional MRI, structural MRI and DTI to investigate the association between alterations in white matter structure, gray matter structure as well as functional activation and functional connectivity in patients with obsessive-compulsive disorder. As there is first evidence indicating that the different symptoms or symptom dimensions of the disorder may be mediated by partially distinct neurobiological entities finding out more about symptom-specific functional and structural alterations constitutes another major aim of our research.