Recording motor-evoked potentials (MEPs) in response to transcranial direct current stimulation (tDCS)?
Compared to TMS which is usually brief and high-intensity, tDCS stimulation protocols are fairly weak and long-duration. This protocol doesn't elicit MEPs by itself, because you need a stronger stimulus.

In some studies (see references below), tDCS has been shown to modulate MEPs, but it is probed by using TMS to elicit the MEP, and comparing the evoked MEPs with and without tDCS.

The mechanistic idea is that tDCS is modulating neuronal thresholds, but you still need some sort of a "kick" to actually evoke a MEP.



Nitsche, M. A., &amp; Paulus, W. (2000). Excitability changes induced in the human motor cortex by weak transcranial direct current stimulation. The Journal of physiology, 527(3), 633-639.

Nitsche, M. A., &amp; Paulus, W. (2001). Sustained excitability elevations induced by transcranial DC motor cortex stimulation in humans. Neurology, 57(10), 1899-1901.

Nitsche, M. A., Fricke, K., Henschke, U., Schlitterlau, A., Liebetanz, D., Lang, N., ... &amp; Paulus, W. (2003). Pharmacological modulation of cortical excitability shifts induced by transcranial direct current stimulation in humans. The Journal of physiology, 553(1), 293-301.