Clinical neuroimaging markers of response to treatment in mood disorders

Mood disorders (MD) are important and frequent psychiatric pathologies, and the management of the patients affected by thes conditions represent an important factor of disability and a huge problem in socialterms and an economic burden. The "in-vivo" studies can help researchers to understand the first events at the base of the development of the pathology and to identify the molecular and non-molecular targets of therapies, but theyhave strong limitations due to the fact that human brain circuitsthem selvesare difficult to be reproduced in animal models. Besides these challenges, they are difficult to be selectively studied with the modern imaging (such as Magnetic Resonance and Positron Emitted Tomography/Computed Tomography) and non-imaging (such as electroencephalography, magnetoencephalography, transcranial magnetic stimulation and evoked potentials) methods.In comparison with other methods, the "in-vivo" imaging investigations have higher temporal and spatial resolution compared to the "in-vivo" non-imaging techniques.All these factors make difficult to fully understand the aetiology and pathophysiology of these disorders, and consequently make difficult not only in the development, but also the monitoring of the actions of therapies,which according to clinical observations have been demonstrated effective in the treatment. In this review, we will focus our attention on the actual state-of-theart of role of imaging in monitoring of treatment of MD, underlying that up to date there are still not standardized imaging markers available in clinical practice.We will analyse briefly the actual classification of MD; then we will focus on the "in vivo" imaging modalities used in research and clinical activity, the current knowledge about the neural models at the base ofMD. Finally the last part of the review focuses on analysis of the principle markers of response to the treatment according to the type of treatment used and to the imaging techniques adopted.