Elucidating Microbiota-Gut-Brain Interactions and Transdiagnostic Symptoms: Approaches Towards Precision Psychiatry

The development of new treatment approaches in psychiatry is urgently needed as mental disorders are the leading cause of years lived with disability worldwide, and many patients cannot benefit from existing options. New approaches for treatment development include the microbiota-brain-gut axis as it plays a crucial role in human behaviour and the examination of transdiagnostic symptoms. These new approaches may reveal underlying mechanisms, which can be used as new treatment targets.
The aim of this thesis is to present the current advances in both approaches including our research and to discuss new developments towards precision psychiatry. Thus, in the first part of this thesis, a randomized controlled trial is presented in which the effects of a probiotic supplement in depressed patients have been examined. The first study, Schaub, Schneider, Vazquez-Castellanos et al. (2022), presents the main results including depressive symptoms, the gut microbiota, and emotional brain processing. The second study, Yamanbaeva, Schaub et al. (submitted), is a multimodal neuroimaging post-hoc analysis exploring effects of the probiotics on brain structure, function, and perfusion using diffusion tensor imaging, resting-state functional MRI, and arterial spin labelling. The second part of the thesis is based on the transdiagnostic approach, and a project on neural correlates of transdiagnostic symptoms is presented. In this study, a neuroimaging approach was used to detect associations between striatal brain volume and anhedonia across multiple mental disorders (Schaub et al., 2021).
In general, the here presented approaches for the development of new treatment options include the detection of underlying biological mechanisms. By identifying multidimensional biomarkers, the stratification of patients for treatment response may be improved and new treatments targeting specific pathophysiological mechanisms can be developed. These advances support the efforts to implement personalised and precision psychiatry in clinical practice.