Upregulating Spinal Circuits to Enhance Balance and Walking and to Increase Spinal Excitability in Older Adults

A high proportion of older adults are currently or soon will be at risk for the well-known decline in walking and balance abilities that occur with aging. Preserving those abilities has become a major public health priority. Balance training can enhance functional abilities or attenuate functional decline; however, age-related motor deficits may impair practice-based motor learning and behavioral performance. Due to the crucial roles of the spinal cord in balance and walking performance, it is important to consider that age-related neural impairment of the spinal cord is a likely contributing factor. Specifically, the spinal cord in older adults has fewer neurons, is less excitable, and conducts signals more slowly.

Despite ample evidence of impaired spinal cord neuronal structure and function with aging, the potential benefit of an intervention targeting spinal control of balance and walking control has been largely unexplored. This dearth of research may be due in part to the lack of a clinically feasible intervention. However, the recent emergence of transcutaneous spinal direct current stimulation (tsDCS) as a non-invasive intervention creates new opportunities for understanding spinal cord contributions to balance and walking performance. Notably, our previous study was the first demonstration of the safety and feasibility of a lab-based intervention that combined tsDCS with complex walking practice. These initial findings support the enhanced efficacy of locomotor learning during a single session when combined with tsDCS in older adults. Building on the success of this preliminary data, the investigators now propose an extended, multisession intervention that combines tsDCS with balance training. The proposed study will be among the first multi-session trial to investigate the effects of tsDCS as an adjunct therapy to dynamic balance training in older adults.

This study aims to enroll 30 older adults aged 65 years or older with balance or walking deficits, determined through objective assessments. All participants will undergo the same five-session balance training over a 2-week period, which will emphasize the use of a unique balance exergaming device called the Dividat Senso. Participants will be randomly assigned to a tsDCS adjuvant group. The "Active group" will receive 30 continuous minutes of 2.5-mA tsDCS over lumbar regions T11/T12. The "Sham group" will receive the sham protocol, which involves an identical montage and stimulation arrangement but delivers no current for 27 minutes. Each 30-minutes session will be preceded and followed by balance and walking assessments to examine the intervention's effects over time. Spinal excitability, measured via soleus H-reflex testing, will be assessed immediately before and after tsDCS at the first and last intervention. Behavioral assessments will occur at baseline, 1 day post-intervention, and 10-day post-intervention to investigate pre vs. post effects and retention intervention effects. Prefrontal activity will be measured using functional near-infrared spectroscopy (fNIRS) during the behavioral assessments to evaluate demand on executive control networks.

The objective of using tsDCS is to upregulate spinal circuits to make them more responsive to task-specific activation, thereby fostering more robust learning and consolidation to enhance performance in dynamic balance tasks. Thus, the overarching hypothesis of the proposed research is that tsDCS will be a potent adjuvant therapy to a dynamic balance intervention by reinforcing task-appropriate spinal excitation to promote skill acquisition and retention, thereby improving balance and walking. This study will focus on achieving the following specific aims:

Specific Aim 1: Acquire preliminary effect size and response variance data to assess whether active adjuvant tsDCS therapy combined with dynamic balance training enhances practice-related gains in balance and walking performance and retention over time.