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 microA/cm(2), 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.
