Abstract TP163: Electrode Montage and Dose of Non-Invasive Stimulation - Considerations for Stroke Recovery Studies

Abstract

Transcranial direct current stimulation (tDCS) is increasingly being used as a possible tool to enhance plasticity in brain regions that might undergo remodeling after a stroke. Our aim was to determine whether dose and montage of tDCS leads to differential changes in regional cerebral blood flow (rCBF) and differential effect on a finger sequence motor learning experiment. Methods: A total of 20 right-handed healthy subjects participated in 6 imaging and 6 motor learning sessions. Brain images of non-invasive blood flow (using arterial spin labelling) were obtained before (6min), during (10min), as well as after (8min) tDCS was applied within the MRI scanner. For the motor sequence learning experiment as well as for the imaging studies, we used three different dose levels (Sham, 2mA, and 4mA) and two different electrode montages (unihemispheric or bihemispheric). In both montages, the anodal electrode (excitability increasing) was placed over the right motor region (C4) while the cathodal electrode (excitability decreasing) was placed either over a left supraorbital region (unihemispheric montage) or over the left motor region (C3; bihemispheric montage). Imaging data were processed and analyzed using SPM12. For the finger sequence learning task, subjects were asked to type a randomly chosen sequence of 7 items (using numbers 2-5 on a computer keyboard) with digits 2-5 of each hand several times before and immediately after a 10 min stimulation period. Results: After unihemispheric and bihemispheric stimulation, left hand showed more improvement in finger sequence learning than right hand, although a linear trend as a function of dose was observed in both montage conditions. rCBF increased during the Stimulation condition and showed a clear linear effect of dose in the peri-rolandic region. Bihemispheric stimulation showed similar, but stronger effects and revealed additional activation of frontomesial regions in the 4mA condition. Conclusion: tDCS dose has an effect on regional surrogate markers of neuronal/synaptic. Effects in a finger sequence learning showed a similar dose effect. Montage (unihemispheric versus bihemispheric) shows differential brain effects, but based on our preliminary analysis no clear behavioral effects.