Objective: Cerebrovascular accidents are the second leading cause of death and the third leading cause of disability worldwide. We hypothesized that cerebellar transcranial direct current stimulation (ctDCS) of the dentate nuclei and the lower-limb representations in the cerebellum can improve functional reach during standing balance in chronic (>6 months' post-stroke) stroke survivors.
Materials and methods: Magnetic resonance imaging (MRI) based subject-specific electric field was computed across a convenience sample of 10 male chronic (>6 months) stroke survivors and one healthy MRI template to find an optimal bipolar bilateral ctDCS montage to target dentate nuclei and lower-limb representations (lobules VII-IX). Then, in a repeated-measure crossover study on a subset of 5 stroke survivors, we compared 15minutes of 2mA ctDCS based on the effects on successful functional reach (%) during standing balance task. Three-way ANOVA investigated the factors of interest- brain regions, montages, stroke participants, and their interactions.
Results: "One-size-fits-all" bipolar ctDCS montage for the clinical study was found to be PO9h-PO10h for dentate nuclei and Exx7-Exx8 for lobules VII-IX with the contralesional anode. PO9h-PO10h ctDCS performed significantly (alpha = 0.05) better in facilitating successful functional reach (%) when compared to Exx7-Exx8 ctDCS. Furthermore, a linear relationship between successful functional reach (%) and electric field strength was found where PO9h-PO10h montage resulted in a significantly (alpha = 0.05) higher electric field strength when compared to Exx7-Exx8 montage for the same 2mA current.
Conclusion: We presented a rational neuroimaging based approach to optimize deep ctDCS of the dentate nuclei and lower limb representations in the cerebellum for post-stroke balance rehabilitation. However, this promising pilot study was limited by "one-size-fits-all" bipolar ctDCS montage as well as a small sample size.
Keywords: cerebellar transcranial direct current stimulation; computational modeling; dentate nucleus.