title: A finite element analysis of the effect of electrode area and inter-electrode distance on the spatial distribution of the current density in tDCS.
abstract: We investigated the effect of electrode area and inter-electrode distance on the spatial distribution of the current density in transcranial direct current stimulation (tDCS). For this purpose, we used the finite element method to compute the distribution of the current density in a four-layered spherical head model using various electrode montages, corresponding to a range of electrode sizes and inter-electrode distances. We found that smaller electrodes required slightly less current to achieve a constant value of the current density at a reference point on the brain surface located directly under the electrode center. Under these conditions, smaller electrodes also produced a more focal current density distribution in the brain, i.e. the magnitude of the current density fell more rapidly with distance from the reference point. The combination of two electrodes with different areas produced an asymmetric current distribution that could lead to more effective and localized neural modulation under the smaller electrode than under the larger one. Focality improved rapidly with decreasing electrode size when the larger electrode sizes were considered but the improvement was less marked for the smaller electrode sizes. Also, focality was not affected significantly by inter-electrode distance unless two large electrodes were placed close together. Increasing the inter-electrode distance resulted in decreased shunting of the current through the scalp and the cerebrospinal fluid, and decreasing electrode area resulted in increased current density on the scalp under the edges of the electrode. Our calculations suggest that when working with conventional electrodes (25-35 cm(2)), one of the electrodes should be placed just 'behind' the target relative to the other electrode, for maximum current density on the target. Also electrodes with areas in the range 3.5-12 cm(2) may provide a better compromise between focality and current density in the scalp than the traditional electrodes. Finally, the use of multiple small return electrodes may be more efficient than the use of a single large return electrode.
authors.affiliation: Institute of Biophysics and Biomedical Engineering, University of Lisbon, Lisbon, Portugal. paula.faria@ipleiria.pt
authors.forename: Paula
authors.initials: P
authors.lastname: Faria
authors.forename: Mark
authors.initials: M
authors.lastname: Hallett
authors.forename: Pedro Cavaleiro
authors.initials: PC
authors.lastname: Miranda
mesh_terms: D004558:Electric Stimulation / Q000295:instrumentation / Q000379:methods; D004566:Electrodes / Q000592:standards; D020342:Finite Element Analysis; D008959:Models, Neurological
references.citation: IEEE Trans Biomed Eng. 2003 Jun;50(6):754-67
references.pmid: 12814242
references.citation: Annu Int Conf IEEE Eng Med Biol Soc. 2009;2009:1596-9
references.pmid: 19964541
references.citation: Trends Cogn Sci. 2008 Dec;12(12):447-54
references.pmid: 18951833
references.citation: Epilepsia. 2006 Feb;47(2):335-42
references.pmid: 16499758
references.citation: J Physiol. 2000 Sep 15;527 Pt 3:633-9
references.pmid: 10990547
references.citation: IEEE Trans Biomed Eng. 2001 Apr;48(4):434-41
references.pmid: 11322531
references.citation: J Neural Eng. 2008 Jun;5(2):163-74
references.pmid: 18441418
references.citation: J Neurol Neurosurg Psychiatry. 2009 Apr;80(4):444-7
references.pmid: 18977813
references.citation: J Physiol. 2004 May 15;557(Pt 1):175-90
references.pmid: 14978199
references.citation: IEEE Trans Biomed Eng. 1969 Jan;16(1):15-22
references.pmid: 5775600
references.citation: J Neurophysiol. 2007 Apr;97(4):3109-17
references.pmid: 17251360
references.citation: Clin Neurophysiol. 2003 Nov;114(11):2220-2; author reply 2222-3
references.pmid: 14580622
references.citation: Electroencephalogr Clin Neurophysiol. 1991 Feb;81(1):47-56
references.pmid: 1705219
references.citation: Clin Neurophysiol. 2009 Jun;120(6):1183-7
references.pmid: 19423386
references.citation: Electroencephalogr Clin Neurophysiol. 1985 Oct;61(4):272-86
references.pmid: 2411506
references.citation: Bipolar Disord. 2006 Apr;8(2):203-4
references.pmid: 16542193
references.citation: Neuroreport. 2005 Sep 28;16(14):1551-5
references.pmid: 16148743
references.citation: IEEE Trans Biomed Eng. 1987 Apr;34(4):289-96
references.pmid: 3504203
references.citation: Comput Biol Med. 2005 Feb;35(2):133-55
references.pmid: 15567183
references.citation: IEEE Trans Biomed Eng. 1997 Mar;44(3):220-3
references.pmid: 9216137
references.citation: Med Biol Eng Comput. 2005 May;43(3):335-43
references.pmid: 16035221
references.citation: Clin Neurophysiol. 2010 Jul;121(7):987-91
references.pmid: 20181514
references.citation: Clin Neurophysiol. 2010 Jul;121(7):1080-4
references.pmid: 20188625
references.citation: Brain Stimul. 2008 Jul;1(3):206-23
references.pmid: 20633386
references.citation: J Neurosci Methods. 2010 Jul 15;190(2):188-97
references.pmid: 20488204
references.citation: Brain Res Bull. 2007 May 30;72(4-6):208-14
references.pmid: 17452283
references.citation: IEEE Trans Biomed Eng. 2011 Jun;58(6):1773-80
references.pmid: 21335303
references.citation: Mov Disord. 2006 Oct;21(10):1693-702
references.pmid: 16817194
references.citation: IEEE Trans Biomed Eng. 1993 Jun;40(6):517-28
references.pmid: 8262533
references.citation: IEEE Trans Biomed Eng. 1996 Sep;43(9):939-43
references.pmid: 9214809
references.citation: Neuroimage. 2007 Apr 15;35(3):1113-24
references.pmid: 17337213
references.citation: Neurology. 2005 Mar 8;64(5):872-5
references.pmid: 15753425
references.citation: Neuroimage. 2010 Jul 15;51(4):1310-8
references.pmid: 20350607
references.citation: Clin Neurophysiol. 2006 Jul;117(7):1623-9
references.pmid: 16762592
references.citation: Med Biol Eng Comput. 1991 May;29(3):261-8
references.pmid: 1943258
references.citation: Anesth Analg. 1968 Nov-Dec;47(6):717-23
references.pmid: 4972743
references.citation: Brain Stimul. 2009 Oct;2(4):215-28, 228.e1-3
references.pmid: 20161507
references.citation: J Affect Disord. 2009 Nov;118(1-3):215-9
references.pmid: 19286265
references.citation: Neurology. 2001 Nov 27;57(10):1899-901
references.pmid: 11723286
references.citation: Brain Stimul. 2009 Oct;2(4):201-7, 207.e1
references.pmid: 20648973
references.citation: Clin Neurophysiol. 2006 Apr;117(4):845-50
references.pmid: 16427357
references.citation: J Physiol. 1927 Sep 9;63(4):357-77
references.pmid: 16993895