Transcranial electric stimulation (tES) during magnetoencephalography (MEG): perspectives and limitations

The ability to modulate brain physiology using non-invasive transcranial electric stimulation (tES), led to a large body of experimental work aiming at identifying causal links between brain structures, physiology and behavior. However, the direct effects of tES on brain oscillatory activity is still not well understood as stimulation-dependent electromagnetic artifacts impede reliable neurophysiological recordings. Recently, we solved this problem using whole-head magnetoencephalography (MEG) and synthetic aperture magnetometry (SAM) beamforming. Here we give an overview of the technical and physical limitations of this new strategy, and present our latest findings on the effects of tES (e.g. transcranial direct current stimulation, tDCS, and transcranial alternating current stimulation, tACS) on brain oscillatory activity. Our studies show that combination of whole-head magnetoencephalography (MEG) and tES is a powerful tool to test some basic hypotheses addressing the link between brain physiology, function and human behavior.