Intermittent theta burst stimulation over the dorsomedial prefrontal cortex modulates resting-state connectivity in depressive patients: A sham-controlled study

The mechanisms underlying repetitive transcranial magnetic stimulation (rTMS) treatment are largely unknown. Although there is a general lack of sham controlled studies, findings show altered functional connectivity to the stimulated region following treatment. When targeting the dorsolateral prefrontal cortex (dlPFC), connectivity with the subgenual anterior cingulate cortex (sgACC) is predictive of response, but less is known about the effects on functional connectivity of targeting the dorsomedial PFC (dmPFC). Here, 30 patients with an ongoing depressive episode were recruited and randomized to 20 sessions at target intensity of either active or sham intermittent theta burst stimulation (iTBS) over dmPFC. Those receiving sham were offered active treatment in a subsequent open phase. A seven minute resting-state scan and depressive symptom assessment was performed before and after treatment. After exclusions due to attrition and excessive head movements 23 patients remained for analysis. Seed-based resting-state connectivity was calculated using two seeds for the dmPFC target as well as the sgACC. A symptom related increase in dmPFC connectivity after active treatment, compared to sham treatment, was found. The effect was observed in a region overlapping the precuneus and the posterior cingulate cortex (PCC), suggesting an increase in the connectivity between the targeted salience network and the default mode network mediating improvement in depressive symptoms. Connectivity between the precuneus and both the sgACC and the treatment target was predictive of symptom improvement following active treatment. The findings have implications for understanding the mechanisms behind iTBS and may inform future efforts to individualize the treatment.