Resting-state Functional Connectivity Throughout a Course of iTBS in Major Depression

The immense disease burden of major depressive disorder (MDD) and unsatisfactory response rates to pharmacological and psychological interventions highlight the need for further development of treatment alternatives. The development of these alternatives relies on an understanding of the pathophysiology of depression, which has, despite considerable efforts, remained largely elusive. Findings have converged on the proposition that depression cannot be attributed to a singular factor and is better understood as a dysfunctional interaction of multiple parameters. At the neural level, depression is described as a dysfunction of several cortical and sub-cortical networks associated with affective salience, cognitive control and self-reverential thoughts. Encouragingly, several studies have shown that pathological alterations in one of these networks, the Default Mode network, may normalize following several weeks of treatment using repetitive transcranial magnetic stimulation (rTMS), an accepted treatment for major depression. The present study aims to elucidate the time course of this modulatory effect on the different networks showing pathological connectivity profiles. Specifically, our aim is to obtain several measurements of functional connectivity and concomitant measures of the symptoms of depression prior to, throughout, and following the 4 week treatment course of iTBS, a faster but equally effective non-invasive brain stimulation technique compared to rTMS. Due to the fact that weekly changes in network connectivity are expected to be relatively small, the stronger BOLD Signal at 7T and the fact that peak temporal correlation coefficients calculated between network nodes have been shown to be significantly higher at 7T than 3T (e.g.) in the Default Mode network should greatly aid in detecting these differences. At each of the 7 measurement time points, fluctuations of BOLD signal will be recorded during a rs-fMRI scan lasting about 15 minutes. Our approach will allow to characterize the temporal profiles of the antidepressant effects of iTBS, thereby furthering our understanding of the mechanism by which iTBS contributes to the normalization of pathological neural connectivity and the reduction of depression symptoms. This proposed longitudinal functional imaging of therapeutic changes is highly relevant to the field of clinical neuroscience and should further advance our understanding of the pathophysiology of depression.