Spinal Networks of Balance Learning and Retention 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.

Specific Aim 2: Establish evidence of increased spinal excitability following tsDCS, positively correlating with gains in balance and walking functions.

The long term deliverable of this line of research will be a clinically feasible multi-modal intervention to assist in preserving motor function and independence in older adults. The knowledge and experience gained from this study will enable us to conduct larger studies to better understand the effects of aging on the spinal cord and to test rehabilitation interventions to promote healthy aging among older adults.

Inclusion criteria

• age range: 65 to 95 years
• no severe high blood pressure: Resting systolic < 180 mmHg and diastolic < 100 mmHg
• no severe vision impairment: Visual acuity ≥ 20/70 as determined by Snellen eye chart
• walking problem: Preferred walking speed slower than 1.0 m/s over 10 meters
• balance problem: Berg Balance Scale score < 45
• no cognitive impairment: Montreal Cognitive Assessment (MoCA) score ≥ 26 out of 30

Exclusion criteria

• diagnosed neurological disorder or injury of the central nervous system, or observation of symptoms consistent with such a condition (Alzheimer's, Parkinson's, stroke, etc.)
• severe arthritis, such as awaiting joint replacement
• current cardiovascular, lung or renal disease; untreated diabetes; terminal illness
• myocardial infarction or major heart surgery in the previous year
• cancer treatment in the past year, except for nonmelanoma skin cancers and cancers having an excellent prognosis (e.g., early stage breast or prostate cancer)
• current diagnosis of schizophrenia, other psychotic disorders, or bipolar disorder
• currently taking medications that affect the central nervous system, such as benzodiazepines, anti-cholinergic medication, and GABAergic medication, among others
• uncontrolled hypertension at rest (systolic > 180 mmHg and/or diastolic > 100 mmHg)
• bone fracture or joint replacement in the previous six months
• current enrollment in any other clinical trial
• planning to relocate out of the area during the study period
• non-English* speaking, due to the likelihood of difficulties following instructions and communicating remotely
• clinical judgment of the investigative team