This study estimated thresholds and locus for human phosphene perception during non-invasive transcranial alternating current stimulation at 20, 50, 60, and 100 Hz. Perception depended significantly on stimulation intensity, with the lowest threshold at 20 Hz and no reported phosphenes at 100 Hz. The authors report dosimetry consistent with a retinal origin and frame the findings as relevant for informing cautious ELF exposure limits in safety guidelines.

This in vitro study exposed glioblastoma (CT2A), neuroblastoma (N2A), and non-tumor astrocyte (C8D1A) cell models to a 100 μT magnetic field across 20–100 Hz for 24–72 hours. The abstract reports decreased viability and proliferation in the tumor cell models within a frequency window centered at 50 Hz, while astrocyte viability increased at 20 and 40 Hz. The authors conclude that frequency is a key determinant of cell-type-specific responses consistent with a “biological window” model.