English: Transcranial electrical stimulation is a specific subgroup of non-invasive brain stimulation techniques, which is based on the application of low-intensity electrical current. While tDCS uses constant current intensity, tRNS and tACS use oscillating current. The vertical axis represents the current intensity in milliamp (mA), while the horizontal axis illustrates the time-course. Abbreviations: tDCS, transcranial direct current stimulation; tRNS, transcranial random noise stimulation; tACS, transcranial alternating current stimulation.