Reproducible magnetophosphene thresholds induced by transcranial alternating magnetic stimulation in humans: a replication study

Magnetophosphenes, flickering visual percepts induced by extremely low-frequency magnetic fields (ELF-MF), represent the most sensitive and reproducible human response to induced electric fields and form a cornerstone of international exposure guidelines. Transcranial Alternating Magnetic Stimulation (tAMS), a recent non-invasive stimulation method, can elicit magnetophosphenes without scalp sensations, but its reliability and underlying mechanisms require replication for further validation. This replication study quantified magnetophosphene perception thresholds in 62 healthy participants exposed to sinusoidal magnetic fields (0-50 mT) at 20, 50, and 60 Hz. Three stimulation configurations were tested: retinal (RET), global head (GLO), and occipital (OCC). Perception probability was modeled using mixed-effects logistic regressions based on rate of change of magnetic flux density over time (dB/dt) as the primary metric. tAMS robustly induced magnetophosphenes, reproducing the threshold patterns reported by Legros et al. (2024). RET and GLO exposures produced steep dose-response curves and low thresholds, whereas OCC stimulation yielded minimal effects. Thresholds were strongly frequency-dependent, with highest sensitivity at 20 Hz. Regression slopes from the original and replication datasets showed high concordance (r = 0.965), confirming reproducibility. The spatial and frequency profiles consistently support a retinal, rod-mediated origin of magnetophosphenes. This replication study validates tAMS as a reliable method for eliciting magnetophosphenes and confirms their retinal origin across exposure conditions. These results strengthen the use of magnetophosphene thresholds as a benchmark for ELF-MF safety standards and underscore the potential of tAMS as a precise, comfortable, and confound-free neuromodulation tool for future diagnostic and therapeutic applications.