The Brain-Heart-Gut Connection

Major Depressive Disorder (MDD) often co-occurs with cardiovascular and gastrointestinal symptoms, highlighting the importance of the brain-heart-gut connection in developing comprehensive treatments. Previous research suggests that key hubs in the depression network, such as the dorsolateral prefrontal cortex (DLPFC) and the subgenual anterior cingulate cortex (sgACC), overlap with structures that are involved in autonomic control, particularly the vagus nerve. Repetitive transcranial magnetic stimulation (rTMS) to the left DLPFC is an established treatment for MDD; however, antidepressant efficacy varies greatly across individuals, and optimal DLPFC targeting remains a significant challenge. Personalized rTMS based on DLPFC-sgACC connectivity improves outcomes but is limited by practical and financial constraints. Recently, rTMS-induced heart-brain coupling (HBC) has emerged as a promising method to utilize heart rate responses to guide treatment. The primary goal of this project is to personalize HBC to improve DLPFC-based targeting for the treatment of MDD while also probing additional readouts of the frontal-vagal system. In Study Arm 1, we will implement an innovative frontal mapping technique to identify the personalized "Grid-Spot" that elicits the strongest HBC in healthy participants. In subsequent visits, we will compare heart rate responses during the 10Hz "Dash" protocol between the "Grid-Spot", conventional DLPFC targeting using "Beam-F3" and an active control region (Cz). Additionally, we will integrate various autonomic nervous system (ANS) measures, including gut motility, pupil dilation and electrodermal activity (EDA), to explore the brain-heart-gut axis and assess their utility in improving target engagement. Furthermore, we will extend our methodology to the personalized application of high-definition transcranial direct current stimulation (HD-tDCS). Specifically, we will explore the effects of anodal versus sham HD-tDCS over the HBC-guided "Gr