Effects of tDCS Dose and Electrode Montage on regional cerebral blood flow and motor behavior

Abstract

We used three dose levels (Sham, 2mA and 4mA) and two different electrode montages (unihemispheric or bihemispheric) to examine DOSE and MONTAGE effects on regional cerebral blood flow (rCBF) as a surrogate marker of neural activity, and on a finger sequence task, as a surrogate behavioral measure drawing on brain regions targeted by transcranial direct current stimulation (tDCS). We placed the anodal electrode over the right motor region (C4) while the cathodal or return electrode was placed either over a left supraorbital region (unihemispheric montage) or over the left motor region (C3 in the bihemispheric montage). Performance changes in the finger sequence task for both hands (left hand: p = 0.0026, and right hand: p = 0.0002) showed a linear tDCS dose response, but no effect of montage. rCBF in the the right hemispheric perirolandic area increased with dose under the anodal electrode (p = 0.027), while in the perirolandic ROI in the left hemisphere, rCBF showed a trend to increase with dose (p = 0.053), and significant effect of montage (p = 0.00004). The bihemispheric montage showed additional rCBF increases in frontomesial regions in the 4mA condition but not in the 2mA condition. Furthermore, we found correlations between rCBF changes in the right perirolandic region and improvements in the finger sequence task performance (FSP) for left and right hand. Our data support not only a strong direct tDCS dose effect for rCBF and FSP as surrogate measures of targeted brain regions, but also indirect effects on rCBF in functionally connected regions (e.g., frontomesial regions), particularly in the higher dose condition, and on FSP of the ipsilateral hand (to the anodal electrode). At higher dose and irrespective of polarity, a wider network of sensorimotor regions is positively affected by tDCS.

Multielectrode Network Stimulation (ME-NETS) demonstrated by concurrent tDCS and fMRI

“…Yet, the effect of tDCS on functional connectivity varies considerably across studies, with studies reporting increased connectivity (Amadi et al, 2014;Krishnamurthy et al, 2015;Sotnikova et al, 2017), decreased connectivity (Antonenko et al, 2017;Dedoncker et al, 2019;Ficek et al, 2018), mixed effects (Mondino et al, 2016;Shahbabaie et al, 2018), and even no effect (Dissanayaka et al, 2017). These differences may be explained by factors such as the polarity and placement of electrodes (Li et al, 2019), the brain state during stimulation or training (Li et al, 2019;Sotnikova et al, 2017), and the dose/duration of stimulation (Shinde et al, 2021).…”