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Brain Advance Access published online on June 15, 2009
Brain, doi:10.1093/brain/awp154
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© The Author (2009). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Bidirectional alterations of interhemispheric parietal balance by non-invasive cortical stimulation

R. Sparing1,2, M. Thimm2, M. D. Hesse1,2, J. Küst3, H. Karbe3 and G. R. Fink1,2

1 Department of Neurology, University Hospital Cologne, Cologne, Germany 2 Institute of Neuroscience and Medicine (INM-3), Cognitive Neurology, Research Centre Juelich, Juelich, Germany 3 Neurological Rehabilitation Centre Godeshöhe, Bonn, Germany

Correspondence to: Dr Roland Sparing, Department of Neurology, University Hospital Cologne, Kerpenerstr. 62, 50924 Cologne, Germany E-mail: roland.sparing{at}uk-koeln.de

Transcranial direct current stimulation is a painless, non-invasive brain stimulation technique that allows one to induce polarity-specific excitability changes in the human brain. Here, we investigated, for the first time in a ‘proof of principle’ study, the behavioural effect of transcranial direct current stimulation on visuospatial attention in both healthy controls and stroke patients suffering from left visuospatial neglect. We applied anodal, cathoP:dal or sham transcranial direct current stimulation (57 µA/cm2, 10 min) to the left or right posterior parietal cortex. Using a visual detection task in a group of right-handed healthy individuals (n = 20), we observed that transcranial direct current stimulation enhanced or impaired performance depending on stimulation parameters (i.e. current polarity) and stimulated hemisphere. These results are in good accordance with classic models of reciprocal interhemispheric competition (‘rivalry’). In a second experiment, we investigated the potential of transcranial direct current stimulation to ameliorate left visuospatial neglect (n = 10). Interestingly, both the inhibitory effect of cathodal transcranial direct current stimulation applied over the unlesioned posterior parietal cortex and the facilitatory effect of anodal transcranial direct current stimulation applied over the lesioned posterior parietal cortex reduced symptoms of visuospatial neglect. Taken together, our findings suggest that transcranial direct current stimulation applied over the posterior parietal cortex can be used to modulate visuospatial processing and that this effect is exerted by influencing interhemispheric reciprocal networks. These novel findings also suggest that a transcranial direct current stimulation-induced modulation of interhemispheric parietal balance may be used clinically to ameliorate visuospatial attention deficits in neglect patients.

Key Words: cortical plasticity; polarization; electrical stimulation; parietal lobe; neglect

Abbreviations: A, anodal; C, cathodal; ER = error rate; P3/P4, electrode position P3/P4 of the 10/20 EEG system; PPC, posterior parietal cortex; RT, reaction time; (r)TMS, (repetitive) transcranial magnetic stimulation; S, sham; TDCS, transcranial direct current stimulation; TP, time point

Received July 2, 2008. Revised February 8, 2009. Accepted May 4, 2009.


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