OBJECTIVES:This study investigated the feasibility of modulating bilateral corticospinal excitability with different polarities of transcutaneous spinal direct current stimulation (tsDCS) in chronic, incomplete spinal cord injury (SCI).METHODS:Six subjects with chronic incomplete SCI (>12 months post injury) participated in this crossover study. Intervention consisted of 3 sessions, separated by at least 1 week, in which each subject received the conditions cathodal, anodal, and sham tsDCS. Stimulation was delivered at 2.5 mA for 20 minutes with the active electrode positioned over the spinous processes of T10-T11 and the reference electrode over left deltoid. To measure the effects of tsDCS on corticospinal excitability, motor evoked potentials (MEPs) from transcranial magnetic stimulation were measured bilaterally from soleus before and after tsDCS.RESULTS:Five subjects completed all 3 sessions. One subject withdrew after 2 sessions due to complications unrelated to the study. MEPs were measurable in 5 subjects. No significant differences in change of MEP amplitudes were found between the 3 conditions. However, there were trends that indicated laterality of response, particularly with cathodal tsDCS increasing corticospinal excitability contralateral to the reference electrode and decreasing corticospinal excitability ipsilateral to the reference electrode.CONCLUSION:Corticospinal excitability may be modulated with laterality by tsDCS in individuals with chronic, incomplete SCI. Further research is needed to 1) determine whether different placement of the reference electrode can lead to uniform modulation bilaterally, and 2) reveal whether these alterations in corticospinal excitability can lead to improved movement function in individuals with chronic, incomplete SCI.

In cases of moderate-to-severe impairment after stroke, transcranial direct current stimulation at the start, rather than the end, of peripheral nerve stimulation prior to motor training may effect better functional outcomes. Future research with a larger sample size is needed to validate the findings of this proof-of-concept study.

This publication was supported by the National Center for Research Resources and the National Center for Advancing Translational Sciences, National Institutes of Health, through Grant UL1TR000117, and the HealthSouth Cardinal Hill Stroke and Spinal Cord Endowment (1215375670).

Transcranial direct current stimulation (tDCS) is a form of non-invasive brain stimulation that can modulate neuroplasticity (the capacity for brain reorganization). Neuroplastic change correlates with upper extremity (UE) recovery after brain lesions. Different electrode configurations of tDCS paired with UE motor training can have different effects in distinct populations. We are conducting the first randomized, double-blind, placebo-controlled trial to investigate which tDCS configuration may best enhance outcomes of UE motor training for stroke survivors with chronic, severe hemiparesis (i.e., little or no wrist or hand movement). We have assigned subjects to 1 of 4 groups: 1) "Anodal": anodal tDCS to excite ipsilesional motor cortex; 2) "Cathodal": cathodal tDCS to inhibit contralesional motor cortex; 3) "Dual": a simultaneous combination of anodal and cathodal tDCS; or 4) "Sham" tDCS. Intervention (10 sessions) consists of tDCS followed by 3 hours of intensive, task-oriented UE training in each session. Our primary outcome measure is Fugl-Meyer Assessment. Our secondary outcome measures are Action Research Arm Test and Stroke Impact Scale. We have conducted evaluations at baseline and post-intervention. Preliminary results from 26 of (projected) 44 subjects indicate substantially greater improvement for the "Cathodal" group than other groups. These findings differ from evidence about tDCS in rehabilitation of mild-to-moderate hemiparesis. Completion of our study will include full analysis of neuroplastic change associated with intervention.

Stroke is one of the most devastating and prevalent diseases. However, efforts to limit tissue damage in acute stroke have met with only minimal success. Therefore, it is of paramount importance to establish effective therapies for use during long-term stages of recovery. Such therapy can capitalize on neuroplastic change (brain reorganization), which has been associated with recovery of function after brain lesions. Intensive, repetitive motor training is a therapeutic intervention that has been shown to support neuroplastic change and improve motor performance after stroke. Likewise, sensory input in the form of peripheral nerve stimulation (PNS) has been shown to upregulate neuroplasticity and improve motor performance after stroke. However, no studies have evaluated how pairing intensive motor training with various PNS intensities and times may affect motor performance, particularly for subjects with severe upper extremity (UE) hemiparesis after stroke. Here, we describe our ongoing study of whether various intensities and times of delivery of PNS relative to motor training will yield differential effects on UE motor function in subjects with chronic, severe motor deficit after stroke. Our results will facilitate development of a dose-response model for PNS paired with intensive, repetitive motor training, which will help optimize this combinatory intervention for stroke survivors with highest need.