Letter to the Editor: Brief history of transcranial direct current stimulation (tDCS): from electric fishes to microcontrollers

Many other researchers used DC for the treatment of mental disorders during the 19th century and the early part of the 20th century, but the variation of procedures, unclear descriptions, few qualitative details and the misunderstood effect of polarization led to variable and/or inconclusive results. In 1964, motivated by animal studies that reported lasting changes in excitability using prolonged scalp DC stimulation, Lippold and Redfearn used 50-500 µA DC currents in 32 healthy subjects, and reported that anodal current induced an increase in alertness, mood and motor activity, whereas cathodal polarization induced quietness and apathy (Lippold & Redfearn, 1964; Guleyupoglu et al. 2013). Characteristics of tDCS, such as the fact that it is non-invasive, mostly well tolerated and its mild adverse effects, have sparked great interest and increase in clinical studies recently (Brunoni et al. 2012). Journal of Medical Ethics 42 , 211 -215 .26324456 1 Biomedical Engineering Laboratory, Division of Basic Sciences and Engineering, Metropolitan Autonomous University at Iztapalapa, Mexico City, Mexico 2 Department of Clinical Research, National Institute of Neurology and Neurosurgery, Mexico City, Mexico 3 Computational Imaging and VisAnalysis (CIVA) Laboratory, Department of Computer Science, University of Missouri, Columbia, MO, USA