Targeted High-Definition tDCS to Improve Upper Limb Rehabilitation in SCI

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Less than one percent of individuals with a spinal cord injury (SCI) experience complete functional recovery by hospital discharge. Functional deficits can be improved after discharge by combining rehabilitation with a promising experimental technique known as non-invasive brain stimulation. Non-invasive brain stimulation is believed to further improve recovery by promoting advantageous plasticity across neural substrates that survive in the majority of SCIs. Specifically, we have recently shown that a form of non-invasive brain stimulation, called transcranial direct current stimulation (tDCS), can improve muscle strength up to 15% more than rehabilitation alone by increasing the excitability of pathways to the weaker muscles. The rationale of this proposal is that optimizing the application of tDCS would lead to an even better enhancement of outcomes in those with SCI. Specifically, our proposal will build off our previous study in SCI to determine if using a more focal form of tDCS can better improve function of the paretic upper extremity compared to conventional tDCS. Our design is based on our preliminary data that shows HD-tDCS shows a 40% advantage over conventional tDCS in restoring upper limb function. Therefore, we hypothesize that by using focal tDCS, we would increase corticospinal excitability to pathways devoted to weak muscles and improve their contribution to movement control of the paretic upper extremity compared to conventional tDCS. To test our premise, we will perform a randomized, assessor-blinded clinical feasibility trial where 24 subjects with C2-C6 incomplete SCI will receive ten sessions of either conventional tDCS or focal tDCS, with a new approach called high-definition tDCS (HD-tDCS), paired with upper-limb rehabilitation. Our aims will: (1) determine the feasibility of recruiting and retaining subjects for our study, (2) identify how HD-tDCS affects upper extremity function and corticospinal excitability of pathways devoted to weak muscles compared to conventional tDCS. Outcome measures will be collected twice before, after and four weeks after the end of treatment. Upper limb function will be the primary outcome and will be measured using the graded redefined assessment of strength, sensibility and prehension. Corticospinal excitability will be characterized using transcranial magnetic stimulation. Completion of our study will result in an understanding concerning what type of tDCS application (focal vs. non-focal) will be most effective at enhancing upper limb function in SCI rehabilitation.