What transcranial direct current stimulation intensity is best for cognitive enhancement?

In a recent study published in The Journal of Neurophysiology, Ehrardt et al. (Ehrhardt SE, Filmer HL, Wards Y, Mattingley JB, Dux PE. J Neurophysiol 125: 385-397, 2021) report that moderate intensity (1 mA/25 cm²) transcranial direct current stimulation (tDCS) is optimal for improving performance on a stimulus-response matching task, as opposed to a lower 0.7 mA/25 cm² or higher 2 mA/25 cm² dose. This result suggests that behavioral effects of tDCS do not follow a linear dose-response curve. Potential neurobiological and neurocognitive implications of these findings, as well as suggested directions for future research, are discussed.