Maxim Hoe

Lack of motivation (apathy), chronic insomnia, difficulty envisioning a positive future, and suicidal thoughts and behaviors (suicidality) are symptoms or phenomena that appear across psychiatric conditions, such as depression, schizophrenia, or anxiety. Through a transdiagnostic lens, these common psychiatric symptoms were studied in this thesis, focusing on shared mechanisms of specific symptoms across different diagnoses rather than in the context of a single diagnosis. Such a transdiagnostic approach can facilitate the identification of the relevance of symptom presence and progression for the course of psychiatric problems and can facilitate the development of targeted interventions and preventive strategies. A transdiagnostic approach focusing on understanding a specific symptom across prevalent psychiatric disorders or nonclinical populations (e.g., studying the neuropsychological mechanisms of motivation deficits in both clinical and nonclinical populations), instead of examining the phenomenology and underlying mechanisms of a typical symptom in a specific disorder (e.g., studying psychological and neural links of suicidal ideation and behavior in patients with major depressive disorder). A transdiagnostic approach further allows for the exploration of the common etiology and psychopathology related to the brain mechanisms underlying the symptoms in the context of general psychopathology. Furthermore, it allows us to examine the specificity of a symptom for a certain clinical population in comparison to other clinical and non-clinical populations, thereby, providing novel insights into the understanding of the common or specific mechanisms for a certain symptom in different psychiatric disorders. This thesis investigated neurophysiological and psychological links of three common psychiatric symptoms: suicidality (including suicidal ideation and behavior), apathy (a reduction in motivation), and insomnia, through relevant emotional and cognitive processes.

The Research Domain Criteria (RDoC) framework, introduced in 2009, guides researchers to study mental health by integrating multiple levels and types of data, including brain circuits, physiology, behavior, paradigms, and self-report experiences, across six key functional domains (e.g., negative emotional valence, positive emotional valence, cognitive control, social processing, arousal/regulation, and sensory-motor systems). The RDoC recommends a