High-definition transcranial direct current stimulation modulates neural activities in patients with prolonged disorders of consciousness

Despite accumulating evidence about its possible treatment effects on disorders of consciousness (DOC) patients [ [1] Thibaut A. Bruno M.-A. Ledoux D. Demertzi A. Laureys S. tDCS in patients with disorders of consciousness. Neurology. 2014; 82: 1112-1118 Crossref PubMed Scopus (191) Google Scholar , [2] Efthymios A. Evangelia L. Nikos A. Stephanos K. Periklis K. George S. et al. Transcranial direct current stimulation effects in disorders of consciousness. Arch Phys Med Rehabil. 2014; 95: 283-289 Abstract Full Text Full Text PDF PubMed Scopus (113) Google Scholar ], conventional transcranial direct current stimulation (tDCS) has encountered a bottleneck, with little progress as a treatment modality in DOC patients. Multi-channel high-definition tDCS (HD-tDCS), a modification of conventional tDCS, offers enhanced neuromodulation. As compared with conventional tDCS, HD-tDCS offers improved spatial targeting (focality) of stimulation [ [3] Datta A. Bansal V. Diaz J. Patel J. Reato D. Bikson M. Gyri-precise head model of transcranial direct current stimulation: improved spatial focality using a ring electrode versus conventional rectangular pad. Brain Stimul. 2009; 2: 201-207 Abstract Full Text Full Text PDF PubMed Scopus (830) Google Scholar , [4] Villamar M.F. Wivatvongvana P. Patumanond J. Bikson M. Truong D.Q. Datta A. et al. Focal modulation of the primary motor cortex in fibromyalgia using 4x1-ring high-definition transcranial direct current stimulation (HD-tDCS): immediate and delayed analgesic effects of cathodal and anodal stimulation. J Pain. 2013; 14: 371-383 Abstract Full Text Full Text PDF PubMed Scopus (126) Google Scholar ]. Previous studies confirmed that HD-tDCS increased the intensity of the stimulus and prolonged its after-effects [ 5 Roy A. Baxter B. Bin H. High-definition transcranial direct current stimulation induces both acute and persistent changes in broadband cortical synchronization: a simultaneous tDCS–EEG study. IEEE Trans Biomed Eng. 2014; 61: 1967-1978 Crossref PubMed Scopus (76) Google Scholar , 6 Kuo H. Bikson M. Datta A. Minhas P. Paulus W. Kuo M. et al. Comparing cortical plasticity induced by conventional and high-definition 4×1 ring tDCS: a neurophysiological study. Brain Stimul. 2013; 6: 644-648 Abstract Full Text Full Text PDF PubMed Scopus (394) Google Scholar , 7 Villamar M.F. Volz M.S. Bikson M. Datta A. Dasilva A.F. Fregni F. Technique and considerations in the use of 4x1 ring high-definition transcranial direct current stimulation (HD-tDCS). J Vis Exp. 2013; e50309 PubMed Google Scholar ]. Moreover, HD-tDCS has been demonstrated able to improve humans' motor function [ [8] Caparelli-Daquer E.M. Zimmermann T.J. Mooshagian E. Parra L.C. Rice J.K. Datta A. et al. A pilot study on effects of 4x1 high-definition tDCS on motor cortex excitability. Conf Proc IEEE Eng Med Biol Soc. 2012; 2012: 735-738 PubMed Google Scholar ], learning [ [9] Nikolin S. Loo C.K. Bai S. Dokos S. Martin D.M. Focalised stimulation using high definition transcranial direct current stimulation (HD-tDCS) to investigate declarative verbal learning and memory functioning. Neuroimage. 2015; 117: 11-19 Crossref PubMed Scopus (105) Google Scholar ] and working memory [ [9] Nikolin S. Loo C.K. Bai S. Dokos S. Martin D.M. Focalised stimulation using high definition transcranial direct current stimulation (HD-tDCS) to investigate declarative verbal learning and memory functioning. Neuroimage. 2015; 117: 11-19 Crossref PubMed Scopus (105) Google Scholar , [10] Karvigh S.A. Motamedi M. Arzani M. Roshan J.H. HD-tDCS in refractory lateral frontal lobe epilepsy patients. Seizure. 2017; 47: 74-80 Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar ], all of which are components of human conscious behaviors. Therefore, considering its outstanding performance in neural modulation, investigating the effects of HD-tDCS in patients with DOC is worthwhile.