Effects of Brain Stimulation on Cortical Excitability in Healthy Adults: A Validation Study

Variability in motor responses influences the ability to perform everyday tasks and learn new skills. Older adults usually demonstrate larger motor variability than younger adults. Here, we propose a non-invasive transcranial direct current stimulation (tDCS) technique to improve motor control in older adults. We hypothesize that tDCS will reduce finger force variability in older adults. We plan to recruit ten younger and ten older healthy adults. We will also assess the changes in excitability of the brain using transcranial magnetic stimulation (TMS). To achieve our project objective, we first validated both TMS (experiment 1) and tDCS (experiment 2) protocols separately. For experiment 1, five healthy young adults received TMS pulses over the brain with varying interstimulus interval (ISI). We have found that smaller and larger ISIs elicited inhibition and facilitation of the response to TMS, respectively, a finding consistent with the published literature. In experiment 2, one healthy young adult participated in three sessions. We compared the effects of inter-electrode distance for tDCS delivery on the brain’s excitability using TMS. We found that tDCS with 3.5 cm versus 7 cm inter-electrode distance is more effective in modulating the brain’s excitability, when compared with sham stimulation. Currently, we are recruiting more participants to understand the robustness of this finding. Once both tDCS and TMS protocols are validated, we will conduct the proposed project. The new knowledge will help design novel brain stimulation protocols to ameliorate motor impairment in stroke survivors.