Motor cortex-evoked activity in reciprocal muscles correlates with reinforcement of trial-and-error behavioral learning

s / Brain Stimulation 8 (2015) 326e342 339 can be challenging, however. The conventional “5 cm rule” misses DLPFC in u003e1/3 cases. An alternative heuristic, BeamF3, applies a mathematical formula to scalp measurements to locate the F3 EEG site for DLPFC-rTMS. A more elaborate approach uses MRI neuronavigation to target a specific DLPFC stereotaxic coordinate. The concordance between these latter two approaches has not previously been assessed. Objective: To quantify the discrepancy in scalp target location between that obtained using the BeamF3 heuristic vs. MRI-guided neuronavigation for the left DLPFC. Methods: We examined MRIs from n1⁄4100 subjects in a clinical trial of MRI-guided left DLPFC-rTMS. Using Visor 2.0 software, in each subject, we localized the scalp site at minimum Euclidean distance from the target MNI coordinate (X-38 Y+44 Z+26) previously identified as optimal based on clinical efficacy (Fox et al., 2012). We then used Osirix 5.9 software to perform nasion-inion, tragus-tragus, and head circumference measurements on the same subjects’MRIs, and applied the BeamF3 formula.We thenmeasured the geodesic distance between Beam-F3 and MRI-guided scalp sites. Results: BeamF3-to-MRI-guided discrepancies were 0.0001), by 3.5mm 0.65 (SEM). Conclusions: In settings where MRI is unavailable or impractical due to cost or access limitations, the BeamF3 heuristic provides a reasonable approximation to MRI-guided neuronavigation for locating left DLPFC in a majority of subjects. A minor optimization of the heuristic may yield additional concordance.