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

Area of Science:

• Neuroscience
• Biophysics
• Sensory Perception

Background:

• Magnetophosphenes, visual percepts from extremely low-frequency magnetic fields (ELF-MF), are key to international exposure guidelines.
• Transcranial alternating magnetic stimulation (tAMS) is a novel method for inducing magnetophosphenes without scalp sensations, but requires validation.

Purpose of the Study:

• To replicate and validate the reliability and underlying mechanisms of tAMS in inducing magnetophosphenes.
• To quantify magnetophosphene perception thresholds across different stimulation configurations and frequencies.

Main Methods:

• 62 healthy participants were exposed to sinusoidal magnetic fields (0-50 mT) at 20, 50, and 60 Hz.
• Three stimulation configurations (retinal, global head, occipital) were tested.
• Perception probability was modeled using mixed-effects logistic regression based on the rate of change of magnetic flux density (dB/dt).

Main Results:

• tAMS reliably induced magnetophosphenes, with thresholds consistent with prior research.
• Retinal and global head stimulation showed steep dose-response curves and low thresholds, while occipital stimulation had minimal effects.
• Thresholds were frequency-dependent, with highest sensitivity at 20 Hz, and showed high concordance between original and replication data (r=0.965).

Conclusions:

• The study validates tAMS as a reliable method for eliciting magnetophosphenes and confirms their retinal, rod-mediated origin.
• Results strengthen the use of magnetophosphene thresholds for ELF-MF safety standards.
• tAMS shows potential as a precise neuromodulation tool for future applications.