Neglect-like effects induced by tDCS modulation of posterior parietal cortices in healthy subjects

Background Repetitive transcranial magnetic stimulation (rTMS) over right posterior parietal cortex was shown to induce interference on visuospatial perception in healthy subjects. Transcranial direct current stimulation (tDCS) is another noninvasive brain stimulation technique that works modulating cortical activity. It is applied through easy to use, noncostly, and portable devices. Objective/Hypothesis The aim of the current study was to investigate if the novel approach of “dual” stimulation over parietal cortices compared with the unilateral (right) cathodal one is able to induce greater and/or longer-lasting neglect-like effects in normal subjects performing a computerized visuospatial task. Methods Eleven healthy subjects underwent a computerized visuospatial task requiring judgments about the symmetry of prebisected lines in baseline condition, during and after tDCS. Right cathodal and left anodal tDCS were simultaneously applied over homologue posterior parietal cortices in the “dual” approach, whereas right cathodal tDCS was used in the traditional unihemisphere stimulation. Results A significant rightward bias in symmetry judgments as compared with baseline and sham conditions was observed in both the stimulation approaches. With “dual” tDCS compared with cathodal stimulation the effect was stronger and appeared earlier, but no longer-lasting after effects were found. Conclusions We speculate that the resulting modulation of interhemispheric inhibition mediated the additional rightward bias in task performance for “dual” hemisphere compared with unihemisphere tDCS. If “dual” tDCS may better reproduce mechanisms underlying real lesions, it could provide a more suitable model for rehabilitation of negligent patients.