Influence on frog retina of alternating magnetic fields with special reference to ganglion cell activity

The effects of extremely low frequency (e.l.f.) electromagnetic fields on basal systems were studied. Frog retinas were exposed to magnetic fields with frequencies and flux densities that have been shown to induce magnetophosphenes in volunteers. The electrical activity in the retina induced by the field was recorded from the ganglion cell layer with a microelectrode technique. A threshold value was obtained at approximately 20 mT, and a sensitivity maximum at 20 Hz. A significant prolongation (4 ms) of the latency from light stimulus to response in the ganglion cell layer was obtained, if the preparation was simultaneously and continuously exposed to a magnetic field. A study of the reaction of the ganglion cells to light and to magnetic fields showed that those cells which were on-cells during light stimulation became off-cells during magnetic stimulation andvice versa. The magnetic field response occurred within approximately 5 ms. while the light stimulus response occurred only after an average of approximately 85 ms. Addition of Na-aspartate or CoCl₂ extinguished simultaneously the response both to light and to magnetic field stimuli.