Current treatments for Parkinson’s disease (PD) are either associated with side effects, expensive, or their efficacy diminishes over time. Thus, the development of practical, inexpensive and effective long-term, adjunct treatments is needed in PD research. Transcranial direct current stimulation (tDCS) may represent one such intervention with a realistic potential to be translated into clinical practice. The goal of this project is to identify the optimal stimulation parameters for the application of tDCS to improve motor and cortical function in PD.
The project comprises two studies designed to examine the efficacy of different tDCS protocols of improving motor function in PD. The first study will determine the optimal timing of tDCS relative to practice of a motor task to improve motor performance, whereas the second study will examine the optimal intensity of tDCS to improve motor performance. The studies will also determine if motor performance improvements attained in a task practiced in association with tDCS can be generalized to non-trained tasks such as a common clinical measure of motor function (Unified Parkinson’s Disease Rating Scale) and various functional manual dexterity tests. Additionally, transcranial magnetic stimulation will be performed before and after the tDCS interventions to assess selected cortical pathways that are commonly impaired in PD and determine the extent to which tDCS impacts these pathways.
Relevance to Diagnosis/Treatment of Parkinson’s Disease:
The identification of the optimal acute parameters for the application of tDCS should provide important information for the design of long-term clinical studies involving tDCS and PD. The results should also provide valuable guidance toward the development of motor rehabilitation strategies for Parkinson’s disease patients that combine tDCS with traditional interventions.
The project will provide novel insight on the optimal timing and intensity of tDCS application to improve motor function in PD. Thus, the findings of the project will provide significant insight into tDCS as a complementary intervention therapy in PD. Furthermore, important information will be obtained regarding the cortical pathways that may be modulated by tDCS and their possible association with increases in motor function. Therefore, the outcomes should have substantial clinical significance and direct applications to future intervention therapy development.
The interim results of the first study indicate that transcranial direct current stimulation (tDCS) applied both before and during the practice task leads to better performance (~22 and 15 %) compared to SHAM stimulation. The interim results of the second study indicate that tDCS applied at both 1 and 2 mA in the practice task lead to better performance (~13 and 14 %) compared with SHAM stimulation. However, tDCS application did not improve performance in transfer tasks that were not performed in association with tDCS or practiced extensively in either study.
The findings demonstrate that tDCS is a promising modality to improve motor performance in PD as relatively large performance improvements could be made with a single tDCS application of 20 minutes. Thus, these results have provided valuable guidance toward the development of long-term stimulation paradigms performed over weeks or months in PD. Based on studies done in other populations it is likely that long-term stimulation could lead to significantly larger improvements in performance and the transfer of performance improvements to non-trained tasks in PD than those attained following a single application. These issues will be investigated in future research projects.
Presentations & Publications
B Poston, RR Walsh, EL Heisler, and JL Alberts. “Intensity-dependent modulation of motor skill acquisition in Parkinson’s disease by transcranial direct current stimulation.” Society for Neuroscience Annual Meeting in San Diego California in November of 2013
B. Poston, E. L. Heisler, R. R. Walsh, J. L. Alberts. “The Influence Of Transcranial Direct Current Stimulation On Maximal Force Production In Parkinson’s Disease” National Strength and Conditioning Association National Conference in July of 2013.