Using Repetitive Transcranial Magnetic Stimulation to Study the Role of Frontostriatal Circuit in Major Depressive Disorder

Major depressive disorder (MDD) is a common, severe, and often life-threatening illness that involves the body, mood, and thoughts. The natural course of MDD tends to worsen without treatment, while people with MDD can lead healthy and productive lives when the illness is effectively treated. Up to 50% of the patients show no response to current available antidepressants.Two major non-invasive brain stimulation (NIBS) tools have been applied for the treatment of psychiatric diseases so far, transcranial magnetic and direct current stimulation (TMS, tDCS). TMS induces a strong magnetic field (magnetic pulses) through the skull into the brain, which generates electrical currents in brain tissue and induces neuronal firing, leading to after-effects, i.e. neuroplasticity, eventually. Neuronal effects of rTMS has been proven to last beyond the actual time of stimulation, enabling altered brain activity for an extended period of time. Adding on rTMS treatment could even give a chance to treat the physical comorbidities and enhance cognitive function in MDD. Nevertheless, underlying neurobiological mechanism of rTMS treatment remains unclear. Reports showed chronic psychosocial stressors are associated with altered frontal-striatal circuitry activation and connectivity. Indeed, aberrant fronto-striatal connectivity and reduced sustain fronto-striatal activation were noticed in MDD patients. However, the specific correlations between fronto-striatal connectivity changes and rTMS treatment outcomes in MDD remain unclear. In this study fMRI will be used to measure the possible correlations between the fronto-striatal circuit activation / connectivity with (1) mood symptoms presentations, (2) neurocognitive measurements, (3) HPA and ANS activities, and (4) immune and metabolic status (cytokines, adipokines and insulin levels) in patients with MDD. Then the possible changes in fronto-striatal FC over a four-week treatment course with 10 Hz rTMS stimulation to left dorsolateral