OP 12. Effects of transcranial static magnetic field stimulation (tSMS) over the human visual cortex: Behavioural and electrophysiological effects

• Published in: Clinical neurophysiology Vol. 124; no. 10; pp. e62 - e63
• Main Authors: Gonzalez-Rosa, J.J, Soto-Leon, V, Foffani, G, Strange, B, Oliviero, A
• Format: Journal Article
• Language: English
• Published: Elsevier Ireland Ltd 01.10.2013
• Subjects: Neurology
• ISSN: 1388-2457; 1872-8952
• DOI: 10.1016/j.clinph.2013.04.079

Question We previously reported that continuous application of Transcranial Static Magnetic Field Stimulation (tSMS) over the motor cortex induces a reduction of cortical excitability lasting several minutes after the end of tSMS. In the present study, we further explore static magnetic field effects on EEG oscillations in the visual cortex and during visual attentional performance in healthy humans. We specifically test a hypothesis that our previous tSMS effects in motor cortex could be related to an increase of alpha band activity, and therefore, associated with an “inhibitory” effect. Methods Thus, we investigated the effects of tSMS (real or sham) placed over visual cortex in two studies: a first experiment, in which tSMS was simultaneous applied during ten minutes eyes-open resting EEG recording; a second experiment, in which visual attention was measured in the context of tSMS during performance of a visual search paradigm. In both experiments, EEG and behavioural measurements were made during, and 10 min following, tSMS application. Results As predicted, the application of real, but not sham, tSMS over the visual cortex resulted in a significant increase in alpha band power. In the visual search task, real and sham tSMS groups displayed a similar behavioural profile, with reaction times (RTs) increasing with increasing task demands. Critically, however, a significant slowing of RTs emerged on trials with the highest difficulty levels during real in comparison to sham tSMS. Conclusions Our results therefore suggest that tSMS has a profound influence on oscillatory alpha activity, which we suggest reflects a modulation of visual cortical excitability. Secondly, our behavioural results indicate that tSMS over the occiput alters visual search performance, slowing responses to stimulus detection. Importantly, this was not a general task impairment, but a tSMS-induced slowing of visual search specific to high attentional load levels. We speculate that this slowing is secondary to a decrease in underlying alpha oscillations. Further studies using tSMS are required to extend the knowledge of the functional significance of brain oscillations changes induced by the application of small magnets over the scalp.