[Effect of a static 0.2 T magnetic field on the EEG power spectrum in periodic median nerve stimulation].

In static magnetic fields as used in n.m.r. equipment for clinical diagnosis we found an increase of the beta-EEG power value at the right hemisphere when stimulating simultaneously the N. medianus of the left hand with a periodicity of 140 ms. By a sequence of 120 ms there was no change of the power in this frequency band. But when stimulating continuously and switching on and off the magnetic field, in the beta- and alpha-frequency bands the power values of the left hemisphere were increased by the influence of the magnetic field, not depending of the field vector. In contrast to these data, in the beta-band the values increased at the right hemisphere, and, additionally are influenced by the field vector. Artifacts in the single frequency bands by the stimulus frequency itself could be excluded. The increase of power value only by a 140 ms-periodicity might be a hint that a "Zeitgeber"-function is activated by this external frequency.