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

Abstract

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.

Transcranial Electrical Stimulation as a Tool to Enhance Attention

“…Indeed, they report a decrease in reaction time for targets presented in the left (contralateral), but not the right hemifield (ipsilateral). Likewise, contralateral target detection was also found to improve with anodal stimulation in another study (Sparing et al 2009). However, Filmer et al (2015) found diminished performance for both contralateral and bilateral stimuli following anodal tDCS.…”

“…However, in the healthy brain, boosting one network function with tES may incur a cost to another network function. For example, while cathodal parietal tDCS enhanced attention to ipsilateral stimuli, it worsened performance for contralateral and bilateral stimuli (Filmer et al 2015;Sparing et al 2009). Similarly, an improved ability to focus attention in a top-down manner (e.g., on the road when driving) may hamper bottom-up attention to unexpected, albeit potentially relevant stimuli (e.g., a child next to the road).…”

“…Cathodal stimulation over the parietal cortex increased performance for ipsilateral targets (Sparing et al 2009), but decreased performance for contralateral targets and also bilateral stimuli (Filmer et al 2015;Sparing et al 2009). Possibly, the representation of the ipsilateral stimulus is enhanced by cathodal stimulation, captures attention, and biases awareness to just that one stimulus.…”

“…For example, Sparing et al (2009) administered anodal tDCS to the right parietal cortex or cathodal tDCS to the left parietal cortex in neglect patients with right hemisphere lesions. Both protocols abolished the rightward bias in line bisection and produced a small leftward bias.…”

Without Blinking an Eye: Proactive Motor Control Enhancement

“…tDCS is a non-invasive, painless cortical stimulation technique which can increase or decrease brain excitability by adjusting the polarity of a weak current flow (Nitsche and Paulus 2000). Various tDCS studies have applied different stimulation protocols manipulating a variety of cognitive abilities such as language (e.g., Cerruti and Schlaug 2009;Flöel et al 2008), attention (e.g., Bolognini et al 2010;Kraft et al 2010;Sparing et al 2009), memory (e.g., Berryhill et al 2010;Chi et al 2010), and executive functions (e.g., Boggio et al 2010;Fregni et al 2005;Jacobson et al 2011). The aim of the present study was therefore to investigate whether modulating activity in the rIFG by using tDCS can enhance proactive inhibitory control of an urge-driven behavior-EB.…”