INFLUENCE OF A STATIC MAGNETIC-FIELD OF 1.0T ON MAGNETIC MOTOR EVOKED-POTENTIALS

The influence of a static magnetic field of a magnetic resonance-imager on latency, amplitude, area, duration, central motor conduction time and duration of the silent period of evoked potentials of the right thenar by transcranial magnetic stimulation were evaluated. (In a pilot study there was no significant influence on transcranial magnetic potentials before and after a magnetic resonance tomography of the brain; n = 9). Investigations were done before and directly after an exposure to the static magnetic field lasting ten minutes (n = 10) and thirty minutes (n = 6) respectively; transcranial magnetic potentials were recorded during pre-innervation of the target muscle without any significant alteration. With the target muscle at rest, however, there was a significant (p < 0.05) facilitation of amplitude and area immediately after a ten minute exposure to the static magnetic field. This facilitation was absent at the end of each trial. Our results argue for the hypothesis of occurring cancellation of effects of a static magnetic field by activation (pre-innervation, stimulation) of the investigated motor system.