IS 17. Effects of focal static magnetic fields on the human cortex

Abstract

The non-invasive modulation of motor cortex excitability by the application of static magnetic fields through the scalp was investigated in healthy humans. Static magnetic fields were obtained by using cylindrical NdFeB magnets. (tSMS) in conscious subjects. We observed an average reduction of motor cortex excitability of up to 25%, as revealed by TMS, which lasted for several minutes after the end of 10min of static magnetic field stimulation (tSMS). The effect of tSMS was dose-dependent (intensity of the magnetic field) and duration dependent, but not polarity-dependent. We used transcranial electric stimulation (TES) to establish that the tSMS-induced reduction of motor cortex excitability was not due to corticospinal axon and/or spinal excitability, but specifically involved intracortical networks. We further explored the tSMS effects on EEG oscillations in the visual cortex and during visual attentional performance in healthy humans. We specifically examined the hypothesis that these effects could be related to an increase of alpha band activity, and therefore, associated to an inhibitory effect. During real but not sham tSMS over the visual cortex, there was a significant increase of the alpha band power. Moreover, we observed a similar reaction time (RTs) pattern during real and sham tSMS for most of trials. However, a significant slowing of RTs emerged across those trials with a higher difficulty levels during real in comparison to sham tSMS . Further studies using tSMS are required to extend the knowledge of the functional significance of cortical excitability changes and brain oscillations changes induced by the application of small magnets over the scalp. These results suggest that tSMS using small static magnets may be a promising tool to modulate cerebral excitability in a non-invasive, painless, and reversible way.