A standard coil placement for reliable transcranial magnetic stimulation of the frontoparietal depression network: the 'F5-AF7 method'

BackgroundThe frontoparietal network (FPN) has been strongly implicated in both the development of and recovery from major depressive disorder (MDD), making it a promising target for transcranial magnetic stimulation (TMS) therapy of MDD. However, commonly used TMS targeting approaches often co-stimulate multiple neighboring functional brain networks to varying degrees across individuals. We therefore aimed to develop a clinically feasible, standardized TMS coil placement that enables stronger and more selective stimulation of the FPN without requiring individual neuroimaging or neuronavigation. MethodsWe optimized the placement of a prototypical figure-of-eight coil in a population-based brain template by maximizing simulated electric field (E-field) strength within a representative FPN cluster. Based on this optimized placement, we derived a practical heuristic using EEG electrode positions and simple scalp measurements. The FPN-optimized placement and its heuristic were validated by comparing E-field hotspot coverage of the FPN and other functional networks against a clinically established, standard coil placement (Beam F3 method) in precisely mapped brains of 20 healthy individuals (15 female) and 20 patients with MDD (7 female). We further assessed robustness of FPN stimulation to coil tilt inaccuracies and the role of coil orientation. ResultsThe optimized heuristic places the center of the coil over the F5 electrode and orients its handle along the F5-AF7 axis. This placement yielded significantly stronger and more selective FPN coverage than the established clinical approach. Targeting was largely robust to tilt inaccuracies but sensitive to rotational deviations. DiscussionThis scalp-based F5-AF7 TMS coil placement enables selective and reliable targeting of the frontoparietal depression network in routine clinical settings. Whether it improves antidepressant efficacy compared to established targeting strategies should be evaluated in future clinical trials.