Excellent test-retest reliability of perturbation-evoked cortical responses supports feasibility of the balance N1 as a clinical biomarker

There is a growing interest in measuring cortical activity during balance control for understanding mechanisms of impaired balance with aging and neurological dysfunction. The most well-characterized electrophysiological signal elicited by a balance disturbance is the perturbation-evoked N1 potential. We previously found associations between the N1 and balance ability, suggesting it may be a potential biomarker of balance health. However, a potential biomarker will be limited by its reliability and clinical feasibility, which has yet to be established. Here, we characterized the reliability of the balance N1 within and between sessions over a 1-wk interval in 10 younger and 14 older adults, and over a 1-year interval in a subset of older adults (<i>n</i> = 12). We extracted N1 amplitude and latency from the Cz electrode using an advanced, computationally intensive approach (64 electrodes, many trials). Test-retest reliability was assessed using the intraclass correlation coefficient (ICC). Internal consistency was quantified by split-half reliability using the Spearman correlation coefficient. N1s varied across individuals, yet within individuals, showed excellent test-retest reliability (ICC > 0.9) and internal reliability (<i>r</i> > 0.9). N1 amplitude reliability generally plateaued within six trials, whereas more trials were needed to reliably measure latency. Similar results were obtained using a minimal approach (three electrodes, simple preprocessing) and at the component level (largest contributing N1 source). The N1's stability, reliability, and feasibility make it well suited for potential use as a clinical biomarker. Characterizing N1 reliability in different populations and contexts will be necessary to enhance our understanding, optimize experimental design, and determine its predictive validity (e.g., falls risk).<b>NEW & NOTEWORTHY</b> Prior studies identified associations between the perturbation-evoked N1 potential and behaviors that predict falls, suggesting its potential as a biomarker of balance. We show excellent test-retest reliability of the N1 over a year in older adults, and that a reliable measurement can be obtained within six trials using simplified methods, demonstrating clinical feasibility. This study also guides the design of more powerful N1 experiments, necessary to identify underlying mechanisms and assess clinical utility.