Research Article Effect of the Interindividual Variability on Computational Modeling of Transcranial Direct Current Stimulation Marta Parazzini, 1 Serena Fiocchi, 1 Ilaria Liorni, 1,2 and Paolo Ravazzani 1 1 Consiglio Nazionale delle Ricerche (CNR), Istituto di Elettronica e di Ingegneria dell’Informazione e delle Telecomunicazioni (IEIIT), Piazza Leonardo da Vinci 32, 20133 Milano, Italy 2 Dipartimento di Elettronica, Informazione e Bioingegneria (DEIB), Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy Correspondence should be addressed to Marta Parazzini; marta.parazzini@ieiit.cnr.it Received 2 April 2015; Revised 24 June 2015; Accepted 8 July 2015 Academic Editor: Jens Christian Claussen Copyright © 2015 Marta Parazzini et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Transcranial direct current stimulation (tDCS) is a neuromodulatory technique that delivers low intensity, direct current to cortical areas facilitating or inhibiting spontaneous neuronal activity. his paper investigates how normal variations in anatomy may afect the current low through the brain. his was done by applying electromagnetic computational methods to human models of diferent age and gender and by comparing the electric ield and current density amplitude distributions within the tissues. Results of this study showed that the general trend of the spatial distributions of the ield amplitude shares some gross characteristics among the diferent human models for the same electrode montages. However, the physical dimension of the subject and his/her morphological and anatomical characteristics somehow inluence the detailed ield distributions such as the ield values. 1. Introduction Transcranial direct current stimulation is a noninvasive brain stimulation technique that utilizes low amplitude direct cur- rent to modulate brain excitability, facilitating or inhibiting spontaneous neuronal activity [1]. Its possible applications in clinical neuroscience, as a potential nonpharmacologic, noninvasive, painless, and reversible approach to neurologic disorders, have attracted the interest of many researchers. In the last few years, a lot of clinical studies have been conducted to evaluate the efects of tDCS in the treatment of diferent diseases, from motor, cognitive, and memory processes to depression and pain syndromes, varying the stimulation parameters and the electrode positions [2, 3]. Recently, this technique has also started to be used in pediatric population [4, 5]. he mechanism of tDCS is believed to arise through a modulation of the baseline cortical excitability, caused by a tonic de- or hyperpolarization of the resting membrane potentials in brain regions experiencing current low [1–3]. It has been shown that the efects of tDCS depend on the polarity of the electrodes: anodal tDCS has excitatory efect, while cathodal tDCS has inhibitory efects [1–3]. tDCS montages could be classiied into diferent cate- gories according to the position of the reference electrode: intracephalic or extracephalic. Traditionally, the electrodes montage most widely used is the intracephalic, when both of the two electrodes are attached to speciic locations on the scalp. To avoid undesirable modulation of the cerebral activity due to the combined efects of the two electrodes on the scalp, it has been proposed to use an extracephalic reference electrode, placed outside the scalp area [1–3], oten on the right arm. his position of the reference has been largely used without reporting side efects [6] or safety issues [7, 8]. he increasingly widespread use of this technique and the rising number of clinical applications have boosted the interest in the estimation of the levels of the electric quantities in the brain tissues due to tDCS. his is currently done by electromagnetic computational techniques to guide and optimize tDCS treatment [9]. As a consequence, there has been an increase of publications aiming to quantify the amplitude spatial distribution of the electric ield (E) and of the current density (J) within the human brain tissues during tDCS, by applying various computational methods to Hindawi Publishing Corporation Computational Intelligence and Neuroscience Volume 2015, Article ID 963293, 9 pages http://dx.doi.org/10.1155/2015/963293